CHAPTER 4 ORNAMENTAL FISH
Ornamental fish present an unusual paradox in that they are both well known and unknown to veterinarians. These animals are well known because they can be seen every day in the home aquarium, ornamental pond, pet store, and public aquarium,1 while at the same time they are unknown because knowledge regarding their health care is limited (e.g., in the areas of antibiotic residuals, antibiotic resistance, emerging diseases, antiquated or undocumented diagnostic and surgical techniques, and pain management issues). The purpose of this chapter is to address some of the current and former issues related to the health and well-being of ornamental fish.
Fish represent the largest class of vertebrates, with more than 20,000 different species. This group also represents the largest number of species kept in captivity. While there may be tens or even hundreds of different species from another class of vertebrates kept in captivity, there are likely more than 1000 different species of fish that have been maintained in captivity. A visit to a local pet store will often reveal 50 to 100 different species of fish available for sale at any given time.
There are three major groups of fish kept in captivity: freshwater, brackish water, and saltwater. The fundamental difference among the three groups is the relative density of the water in which they live. Some fish can move between freshwater to brackish water or saltwater to brackish water, but relatively few fish can live in the two extremes (freshwater and saltwater). The various physiologic and anatomic characteristics among freshwater and saltwater fish will be addressed in the following sections.
It would be impossible and impractical to categorize every species of freshwater fish in a single book chapter, so we will present information about the two major groups of fish that are commonly kept in the captivity (freshwater temperate and tropical species) and refer to them as a general classification of bony fishes known as Actinopterygii. In addition, we will also provide more detailed information regarding three of the important groups of captive freshwater fishes: catfish, cichlids, and cyprinids.
Most of the major taxonomic groups are represented by the freshwater temperate species.2 For many, this group represents the species commonly considered as sport fish in the United States. The most common genera of freshwater temperate fishes maintained in captivity include the sturgeon (Acipenser spp.) (Figure 4-1), paddlefish (Polyodon spathula), eels (Anguilla spp.), pike (Esox spp.), bass (Micropterus spp.), sunfish (Lepomis spp.), walleye (Sander vitreus), mullet (Mugil spp.), spotted sea trout (Cynoscion spp.), salmonids, and cyprinids. Although many of these fish are raised by hobbyists, the majority of these species require much larger systems as might be represented in a public aquarium display. Consult an introductory ichthyology text for a more detailed description of the major taxonomic groups of freshwater temperate fish.
Figure 4-1 The sturgeon is a primitive freshwater temperate species. This genus has a wide range of species, representing relatively small sized animals to one of the largest freshwater species of fish. Although they are best known for their eggs (e.g., caviar), at least one species is offered for sale in the pet trade, and several others are routinely maintained in public aquaria.
Freshwater tropical fish represent the largest numbers of animals typically found in home aquaria. Generally, this group of fishes is readily available for a small to moderate investment and can be easily maintained by the novice aquarist or hobbyist. Families of freshwater tropical fish include characins (e.g., tetras: Gymnocorymbus spp., Hemigrammus spp., Hyphessobrycon spp., Paracheirodon spp., Moenkhausia sp.), cyprinids (barbs: Barbus spp.), catfish (e.g., Corydoras spp., Pimelodus spp.), killifish (e.g., Aphyosemion spp., Fundulopanchax spp.), rainbowfishes (e.g., Iriatherina spp., Melanotaenia spp., Glossolepis sp.), gouramies (e.g., Colisa spp., Osphronemus spp., Trichogaster spp.), livebearers (e.g., Alfaro spp., Poecilia spp., Xiphophorus sp.), and cichlids (e.g., Pseudotropheus spp., Labidochromis spp., Iodotropheus sp., Dimidichromis sp., Copadichromis sp., Neolamprologus spp., Apistogramma spp., Microgeophagus sp., Aequidens spp., Cichlasoma spp.).2,3
Catfish (e.g., Ictalurus spp., Lacantunia spp., Corydoras spp., Ancistrus spp., Pimelodus spp., Arius spp., Kryptopterus spp., Phractocephalus spp.) represent one of the largest groups of freshwater fishes, with more than 2000 species. Catfish have a cosmopolitan distribution. Catfish are an important group because they serve many different roles, including as ornamentals (Figure 4-2, A), as food fish in aquaculture (Figure 4-2, B), as research animals, and for sport fishing. Most catfish are found in freshwater, although there are two families that contain saltwater species.2,3 Although catfish have a cosmopolitan distribution, more than 50% of all catfish species are native to South America. There is a high degree of variability in the size and weight of these fish, with animals ranging from 10 cm to over 2 m in length and 10 g to over 300 kg in weight. Most species of catfish are nocturnal. Catfish are primarily benthic or bottom-dwellers. Because of their benthic lifestyle, catfish have sensory structures, barbels that assist them with characterizing food and nonfood items and substrate types in a low-light setting.
The cichlids represent one of the most diverse groups of fish, with representation in North America, Central America, South America, and Africa. These fish are prized for their diversity in size, shape, and color. African lake cichlids are one of the most evolutionarily diverse groups in the world, as many different species have evolved within limited ecologic niches (Figure 4-3). With this rapid evolution have come highly variable morphology, feeding strategies, and dietary needs. Although cichlids can look highly variable from genus to genus, they all have a common “break” in their lateral line system. The lateral line is a mechanosensory structure that assists fish with interpreting events in their environment (e.g., shifts in water pressure suggesting a predator is approaching).
Goldfish (Carassius auratus), koi (Cyprinus carpio), and carp (Cyprinus spp.) are members of the largest family (>2200 species) of freshwater fish, Cyprinidae. Cyprinids have the widest area of distribution of any of the freshwater fish. Southeast Asia is the center of origin for this family of fish; however, many species have been introduced around the world and have readily adapted to these new environments.2 The carp are the largest species from this family and may hybridize with goldfish. Koi (Figure 4-4) are colorful domestic mutations of carp that are highly valued by hobbyists and the commercial pet trade. The koi can be divided into two major classifications: the nonmetallic koi and the metallic koi.2 This division is based on typical color patterns, scale types, shape, and size. Goldfish are not koi but rather descendants of the Crucian carp (Carassius carassius).2 Goldfish remain one of the most popular ornamental species and are often found in garden ponds and home aquaria. These fish generally do best if kept in cool waters (55°–68° F, 12°–20° C) with abundant plant life and adequate aeration. There are more than 30 varieties of ornamental goldfish available in the pet trade today.
Many marine fish species exist, and, again, it would be impossible to cover the diversity of these fishes in a single chapter. Therefore, this chapter will focus on the species most commonly seen in captivity, including marine tropical fish, marine coldwater fish, and the elasmobranchs (e.g., sharks, skates, and rays).2–4
There are approximately 23 categories of marine tropical fish. These 23 groups can be arbitrarily divided into four major groups by their feeding attributes and compatibility with other species (Figure 4-5). Most of these groups are well represented in the aquarium trade and in public aquaria.
The first category of marine tropical fish is the “rapid eater” and includes the angelfish (e.g., Pomacanthus spp.), damselfish (e.g., Amblyglyphidodon spp.), squirrelfish (e.g., Holocentrus spp.), triggerfish (e.g., Balistapus spp., Balistoides spp.), and groupers (e.g., Cephalopholis spp., Variola spp.).2 These fish do well if kept at low densities in the aquarium or if they are provided a large area where overcrowding is not an issue (e.g., large reef tanks in public displays). Hostile interaction is a major concern for these animals, as they can be very food aggressive.2–4 These animals may be kept together quite readily if provided an abundance of food and a diverse diet. Often they are kept in live coral reef tanks with anemones and other species of animals from the same group.2,3
The slow eaters represent the largest subgroup of marine tropical fish. This group includes, but is not limited to, the anemone clown fish (e.g., Amphiprion ocellaris), parrotfish (e.g., Sparisoma spp.), puffers (e.g., Carinotetraodon spp., Tetraodon spp., Colomesus spp.), surgeonfish (e.g., Acanthurus sohal), wrasses (e.g., Cheilinus spp., Halichoeres spp., Hemigymnus spp., Thalassoma spp.), and trunkfish (e.g., Aulostomus spp., Strophiurichthys spp., Ostracion spp.). Compatibility is an issue with this group of animals, and they do best if maintained in large displays with a large amount of hiding area. Although these fish are grouped based on their feeding strategy, there remains a great deal of variability in the diets of these animals.
Another group extreme in feeding habits includes those animals that have difficulty competing for food. This group of animals includes some of the more unusual species, such as the seahorses (Hippocampus spp.), jawfishes (Opistognathus spp., Stalix spp., Lonchopisthus spp.), pipefish (Stigmatopora spp., Lissocampus spp., Corythoichthys spp.), and batfish (Dibranchus spp., Halieutea spp., Halieutichthys spp., Malthopsis spp., Ogcocephalus spp., Zalieutes spp.). Many of these fish are slow swimming and are easily outcompeted by faster swimming fish. Members of this group should be housed together with similar species and monitored closely to ensure that they obtain sufficient calories.
The last group of animals to be categorized as marine tropicals includes the snappers (e.g., Lutjanus spp., Pristipomoides spp., Nemadactylus spp., Etelis spp.) and grunts (e.g., Haemulon spp.). These are reasonably large, territorial schooling fish that are, for the most part, kept at public facilities. They can best be described as “gluttons,” not only for the manner in which they feed but also for the almost insatiable hunger they exhibit. They are virtually fearless in their feeding habits and will attempt to remove food from the jaws of even large predators.2
Although some of the smaller marine coldwater species are used for public display, many are too large to be accommodated in anything other than large aquaria. The majority of the species in this general category are used as commercial food fish. The first group, which represents approximately 70 different species, includes the gadids or cod (e.g., Gadus spp.), haddock (e.g., Melanogrammus spp.), hake (e.g., Urophycis spp.), and pollock (e.g., Theragra spp.). These species are valued as food and for their medicinal value. There are very few public aquaria that exhibit these large species, because they require systems in excess of 1 million gallons of seawater. Tuna (e.g., Thunnus spp., Euthynnus spp., Katsuwonus spp.) have become popular in large open ocean exhibits at public facilities, but only through improved and advanced life support technology and husbandry techniques has it been possible to exhibit this spectacular group of animals. By far the most common category of fish in this group is the flatfish. This group includes, but is not limited to, the flounder (e.g., Platichthys spp., Scophthalmus spp., Limanda spp., Pleuronectes spp., Atheresthes spp.), halibut (e.g., Hippoglossus spp.), and rock sole (Lepidopsetta bilineata). The sablefish (Anaplopoma fimbria) and lumpfish (Paraliparis fimbriatus) are also in this group of fish and are only occasionally represented in public displays.
There are more than 350 species of sharks in the world, and only a small percentage are represented as display animals or kept by private aquarists and hobbyists. The species that are found occasionally in home aquaria include the carpet sharks (e.g., Parascyllium spp.) (Figure 4-6), catsharks (e.g., Galeus spp., Scyliorhinus spp.), and horned sharks (e.g., Heterodontus spp.). Most of the other species of sharks are much too large to be kept in anything less than a public aquarium or large commercial facility. Many public facilities display saw sharks (e.g., Pristiophorus spp.) and multiple species of ornamental sharks, including angel sharks (e.g., Squatina australis), dogfish (e.g., Squalus spp., Scymnodon spp., Deania spp., Centroscymnus spp.), and frilled sharks (e.g., Chlamydoselachus spp.).
Skates and rays are closely related to sharks; however, they are markedly different in appearance (Figure 4-7). There are both freshwater and saltwater varieties of stingrays. The skates and rays are dorsoventrally flattened animals and usually have at least one venomous spine on the dorsal caudal fin (tail). There are multiple freshwater species (Figure 4-8) that are small enough to be kept by the private aquarist; however, the majority of these animals are also found in public facilities. There are a number of ornamental species of saltwater rays, such as the guitarfish (e.g., Rhinobatos spp.), butterfly rays (e.g., Gymnura spp.), and cow-nose rays (e.g., Rhinoptera spp.), that have been maintained and successfully reproduced in public facilities. Many of the larger, saltwater rays, such as the southern stingray (Dasyatis americana), Atlantic stingray (Dasyatis sabina), eagle ray (Myliobatis aquila), and giant manta ray (Manta birostris), are also now being kept in public aquaria.
Figure 4-7 Sharks and stingrays have distinct morphologic features. Note the dorsoventrally flattened shape of the benthic (bottom-dwelling) ray compared to the streamlined pelagic (open water–dwelling) shark.
When veterinarians begin to work with a new species of animal, it is imperative that they develop a basic understanding of the animal’s anatomy and physiology. A background knowledge of anatomy and physiology will prove beneficial when collecting diagnostic samples or administering therapeutics. The following is a review of unique anatomic and physiologic features of fish. (See other resources for additional information regarding this subject.2)
Fish are covered with a mucous coat that is produced by cells in their integument. This mucous coat is an important component of the innate immune system and serves as the first line of defense against pathogenic organisms (e.g., bacteria, fungi, and viruses). The mucous barrier contains various sized proteins (e.g., immunoglobulins) that bind pathogens and prevent invasion. If this protective barrier is penetrated, fish have minimal protection against pathogens. To ensure that this barrier remains intact and undamaged, fish should be handled only when necessary.
The scales of a fish are located in the dermis and provide protection over the musculature. There are four types of scales found on fish: placoid, ganoid, cycloid, and ctenoid. Placoid scales are found on elasmobranchs, and ganoid, cycloid, and ctenoid scales are found on teleosts (e.g., bony fishes). The ganoid and cycloid scales are common on the more primitive species of teleosts, whereas the ctenoid scales are found on the more evolutionarily advanced fish. The scales serve as a protective armor, and damage or loss of the scales may result in the introduction of opportunistic infections. Handling should be minimized to avoid traumatizing the scales.
Teleosts typically have two sets of paired fins (e.g., pectoral and pelvic) and three unpaired fins (e.g., dorsal, anal, and caudal) (Figure 4-9). Fins are used for steering, balancing, and braking. Certain species have modified fins to adapt to certain niches. For example, the anal fin of the knifefish is a large, single fin located on the ventrum of the animal. This fins serves as the animal’s primary source of locomotion. Spines may be associated with some fins and serve as a defense mechanism. The lionfish (Pterois volitans) produces venom that can be injected into a potential predator, causing significant pain and discomfort. Knowledge of the species that produce venom is essential to prevent injury to the handler. Fish may damage their spines when captured in a net. To prevent this, fish may be scooped into a plastic cup or bucket to facilitate removal from the aquarium.
The respiratory system of fish is vastly different from the respiratory systems of higher vertebrates (e.g., reptiles, birds, and mammals). Gills are the primary respiratory organs of most fish, although certain species use accessory organs to aid in the absorption of oxygen. Gills serve to absorb oxygen, excrete waste products (e.g., ammonia and carbon dioxide), and regulate ion and water balance. Teleosts have four pairs of gills; elasmobranchs can have five to seven pairs. The gills are attached to a bony gill arch, and each gill is comprised of primary and secondary lamellae. The secondary lamellae are the site of gas exchange (Figure 4-10). Exposure to parasites and toxic compounds, such as ammonia, results in excessive production of mucus, which can impede gas exchange. The presenting symptoms of affected animals include rapid opercular movements and gulping for air at the water’s surface; among these animals sudden death may occur.
Figure 4-10 A, Healthy gill. B, Abnormal secondary lamellae. The secondary lamellae are the site of gas exchange and ammonia excretion in fish. Damage to these gills can result in reduced gas exchange, ammonia excretion, and death.
(Courtesy Dr. Wes Baumgartner.)
Fish have a simple, inline, two-chambered heart comprised of a single atrium and ventricle. The heart is located ventral to the pharynx and cranial to the liver. Unoxygenated blood is pumped from the heart to the gills, where it is oxygenated and distributed to the rest of the body. Fish possess two portal systems: a renal portal system, which drains blood from the caudal musculature, and a hepatic portal system, which drains venous blood from the digestive tract.
The lateral line is an important mechanosensory structure used by fish to detect changes in sound waves and water pressure. The lateral line originates on the head, around the eyes and nares, and extends along the lateral body wall. When maintained in captivity, certain groups of marine fish, including tangs and angelfish, may develop head and lateral line erosions. The specific causes of this syndrome have not been elucidated, but dietary deficiency, water quality, and infectious disease are all suspected.
Fish can be classified into three different feeding strategies: herbivore, omnivore, or carnivore. The length of the digestive tract can vary depending on feeding strategy. For example, the length of an herbivore’s digestive tract is generally much longer than that of an omnivore or carnivore. The stomach is absent in some species, such as goldfish and carp. Pyloric cecae are found in some species of fish. These structures secrete digestive enzymes and increase the absorptive surface area of the digestive tract. Pyloric cecae are used as a taxonomic indicator in some species. The fish liver is a large structure and is located in the cranial coelomic cavity. The normal color of the liver should be red-brown; however, yellow, fatty livers are a common finding at necropsy. This finding is often the result of diets rich in fats and protein.
The fish kidney is a single structure that is comprised of two segments: anterior and posterior. The kidney is located dorsal to the swim bladder along the body wall. The fish kidney serves as both an osmoregulatory and a hematopoietic organ. The anterior kidney and the interstitium of the posterior segment serve as the primary sites for blood cell and immunoglobulin production in fish, as these animals do not have bone marrow. The posterior kidney primarily regulates electrolyte and urine output. Fish that are found in saltwater (hypertonic) environments tend to lose water and absorb salts. To prevent dehydration, these fish must drink water and excrete excess electrolytes, such as sodium and chloride, through the kidney and gills. Fish that live in freshwater (hypotonic) environments constantly absorb water by osmosis. To prevent overhydration, freshwater fish excrete large volumes of dilute urine.
It is easy to recognize aquatic facilities (institutional or pet retail) that have the most disease problems on the basis of their appearance. There is usually an accumulation of trash, dirty exhibits, dead animals, and a general “unhealthy” appearance to the collection. This does not mean that a “clean” facility is free of disease but that they traditionally have fewer and less severe outbreaks of disease.5 The general husbandry and maintenance of the aquatic facility and ecosystems have a direct relationship to the overall health of the animals. Maintaining clean areas behind the exhibits and nonpublic areas is essential to good health practices.3,5 The same can be said for retail aquarium facilities. Accumulation of feces, excess food, and detritus are predisposing factors to poor water quality and can serve as substrates for facultative pathogens. Cleaning and disinfecting seines, nets, buckets, and tanks are imperative to maintain a high-quality health program at a facility. A dynamic team effort is required to maintain a clean facility and healthy animals, but a clean facility will pay dividends by providing a safer workplace, reduced disease incidence, increased production, and generally healthier fish.
Given ideal environmental conditions, ecosystems require a certain amount of space to fully develop, though quantitatively how much space is a debatable matter. Generally, to place an ecosystem in a very large aquarium or other holding space is not a major ecologic problem, although it might be considered an engineering endeavor. The difficulty arises when veterinarians attempt to scale down and include many components in a much smaller space than which would normally occur in the wild. To miniaturize an ecosystem and place it into a small space for observation, education, or research, veterinarians are immediately faced with a major dilemma, which is to scale the miniature so that it can still function as a reasonable facsimile of the wild ecosystem. This question is intimately related to the entire problem of how veterinarians affect wild environments and how they restore them, as well as how they construct their aquaria.5,6
There is little biologic reason for the traditional “box type” aquarium shape; however, the common reason for its existence is associated with availability and mechanical, aesthetic, and economic convenience (Figure 4-11). For many scientists and aquarists, the ease of purchase and setup of a ready-made tank outweighs all other factors when a water-based system is desired.
Figure 4-11 Historically, all fish tanks were rectangular (A). More recently, there has been a movement by commercial tank manufacturers to create new tank shapes (e.g., bow front tank) (B). These oddly shaped tanks do little for the aquatic ecosystem, and are primarily for aesthetics.
The presence of tank walls that can support benthic communities or allow excessive light is undesirable. A weakly translucent cylindrical tank that minimizes attachment surface for a given volume and has a rotating, cleaning mechanism to keep the surface free of sediment is highly desirable but very expensive.
For the hobbyist, aquarist, or scientist who wishes to construct an efficient model ecosystem, the materials (e.g., glass, plexiglass) are readily available to fabricate any shape or form of enclosure. Only after determining the ideal shape of the desired system, should one be concerned with the aesthetics, viewing, and construction of the aquarium.
Choosing the correct size of tank is an easy task. The main principle to remember is that bigger really is better. The smallest tank size we recommend is the commercially available 20-gallon tank (24″ × 12″ × 20″; 61 cm × 30.5 cm × 50.8 cm); however, the larger tanks provide an even more stable environment for fish. A larger tank also will offer the benefit of a much more liberal air-to-water surface area for the fish. However, with the advancements in life support technology today, it is possible to provide more than adequate life support to maintain large densities of fish in smaller aquaria while also maintaining a greater diversity of animals.4,7,8
The term tropical places too much emphasis on the idea of “high temperature” for all exotic fishes. A number of these ornamental fish are not from the tropics, and quite a few from the tropics do not come from particularly warm water. It is important to recognize that a large number of exotic ornamental fish cannot thrive in cool, chilly water (<68° F or 20° C), because it affects their metabolic rate or immune function; other species cannot thrive in extremely warm water (>86° F or 30° C), because they need more oxygen than the water has the ability to carry. There is no exact degree of heat that is best suited to each species. Most fish tolerate a 10° F fluctuation over time and can stand a 5° F change in a short period of time (e.g., minutes) without consequence.4,5 It is almost impossible to find a place in nature where the temperature falls into the controlled ranges that veterinarians try to achieve in the captive environment, and it would be reasonable to believe that temperature changes can be beneficial and stimulating to the animals. In practice, the aquarium environment should be geared toward the temperature needs of the species of fish that will inhabit the aquarium. It is best to create fish communities from similar ecosystems and attempt to maintain the temperature range as close as possible to the native waters of those particular species. Temperature changes will occur, but if they occur within the basic guidelines mentioned previously, these changes will be beneficial to the well-being of the animals.
In nature, the waste products produced by fish are diluted into the vastness of the body of water and carried away by flowing water, reducing the potential dangers to fish. In closed systems (e.g., home or public aquarium), wastes and toxins can accumulate to levels that are harmful to fish. To avoid this problem, closed systems must be managed using some form of filtration. There are three primary types of filtration: mechanical, biologic, and chemical. These different filtration mechanisms work independently of one another and can be used in combination.
Mechanical filtration represents one of the original forms of filtration used in the home aquarium. This type of filtration removes organic debris from the water by passing it through a filter material (e.g., floss, fiber, or paper cartridge) (Figure 4-12). The amount of filtration that can be accomplished using this type of filter depends on the type and size of the filter material and rate that the water is recirculated through the filter media. A densely packed fiber or small pore size will restrict the size of waste that can pass the filter media, resulting in less waste in the aquarium. Maintenance of these filters requires cleaning or replacement of the floss or cartridge. Mechanical filtration remains an important method of filtration in home aquaria, outdoor ponds, and public aquaria. This type of filtration is best used with other types of filtration (biologic or chemical) to improve the overall quality of water in the system. When a series of filters is used inline, it is best to place the mechanical filter first. This ensures that the heavy organic material will be removed before contaminating or clogging the other filters (e.g., chemical or biologic-sand filter). Mechanical filtration does have limitations; for example, it is not effective in trapping finite particles or chemicals.
Figure 4-12 Mechanical filtration is used to remove detritus from an aquatic system. This type of filtration can be combined with the other methods to improve the overall water quality in a system. For example, this power filter cartridge is comprised of floss (mechanical) and carbon (chemical). Once in the system, it will also be colonized with nitrifying bacteria (biologic).
Ammonia is the primary end product of protein catabolism in fish. In a closed system, this waste product can be fatal to fish. It was the advent of biologic filtration that led to our ability to maintain large densities of fish in small volumes of water. Biologic filtration is the most common type of filtration used in the home aquarium and outdoor pond, and it comes in many different forms (e.g., under-gravel filters, bio-wheels, sand or bead filters, and wet-dry filters) (Figure 4-13). A biologic filter should be selected based upon the expected load on the system. If a large density of fish is going to be maintained in a system or the fish are going to be fed large quantities of food to ensure growth (e.g., aquaculture), then a large surface area for bacteria is needed.
Figure 4-13 Biologic filtration is essential to maintaining fish in closed aquatic systems. There are many different ways to increase the overall surface area in a system to colonize nitrifying bacteria. This filtration method uses plastic balls as a surface for the bacteria.
The biologic filter is comprised of nitrifying bacteria. Although there are numerous types, the two most common genera discussed are Nitrosomonas spp. and Nitrobacter spp. Nitrosomonas spp. are important in denaturing ammonia, the primary waste product produced by fish, into nitrite. Both ammonia and nitrite are toxic to fish. Nitrobacter spp. are responsible for further reducing nitrite to nitrate.
Once an aquarium and biologic filter are colonized, the system becomes self-sufficient. However, there are several factors that can affect the function of a biologic filter, including temperature, oxygen content, and drugs/therapeutics. Nitrobacter spp. are not cold tolerant. Therefore, in outdoor ponds when the water temperature drops below 65° F (18.5° C), nitrite will not be converted into nitrate as rapidly. During those times when the water temperature may drop below 65° F, fish should be fed less food to reduce the load on the system. Nitrosomonas spp. and Nitrobacter spp. are aerobic bacteria. In the well-aerated home aquarium, oxygen levels are often adequate for the bacteria; however, in outdoor ponds, oxygen levels can become depleted on warm summer nights. To reduce the likelihood of biologic filter failure, it is recommended that outdoor ponds be aerated during warm, summer days and nights.
A biologic filter requires time to become established. The amount of time depends upon the temperature of the water and the organic load on the system. New systems should be started slowly, adding only a small number of fish at a time. Closely monitoring the ammonia, nitrite, and nitrate levels on a daily basis is strongly recommended for new systems. Commercial microbial products (Fritzyme; Fritz Industries, Dallas, TX) are available that can expedite the establishment of the filter by seeding the system with bacteria. Water samples, filter pads, or aquarium substrates from established systems have also been used to seed a tank. However, the addition of these products to a new system may lead to the introduction of potential fish pathogens.
There are numerous types of chemical filters in the pet trade. Chemical filtration refers to those filters that remove toxic compounds by binding them or converting them into nontoxic substances. The original form of chemical filtration was activated carbon. Carbon serves as a nonspecific binding agent for a number of different substances. When the binding sites on the carbon are full, they no longer act as filters and need to be replaced or cleaned. Other forms of chemical filtration are more specific, such as the resins that only bind ammonia. There are other forms of chemical filtration, such as ultraviolet (UV) sterilizers and protein skimmers, that alter or trap compounds. UV sterilizers expose compounds to short wavelength light, altering their form and rendering them harmless. UV sterilizers can be used to control certain pathogens and algae. A UV sterilizer has a UV bulb encased in a waterproof sheath within a cylinder. As water passes through the cylinder, the water is exposed to UV light, which can alter the DNA or RNA of the organism. The amount of time that it takes for the water to pass the bulb and the bulb wattage determine the effectiveness of the UV sterilizer. A low-wattage bulb in a short cylinder will have little effect on pathogens. These systems have also been used with great success at controlling algae and pathogens in outdoor ponds. Protein skimmers trap proteins in bubbles so that they can be separated from the water and removed. Chemical filtration, in combination with mechanical or biologic filtration, can improve the water quality dramatically, creating a “healthy” environment for fish.
Correct lighting for the aquarium system depends on several factors, including the quality of the light emitted from the selected light source. Full-spectrum lighting is preferred. This type of lighting provides the three primary light spectrums: ultraviolet, visible, and infrared. The various spectrums can be affected by water depth, with certain spectrums (e.g., ultraviolet) being removed in the epilimnion (upper water level). Another important factor is the function of the system. If the tank is going to house deep-water African cichlids, lighting becomes less important; however, if the lighting system is needed for a reef tank that is going to be stocked with corals, a significant quantity of high-quality full-spectrum light will be required. The primary disadvantages associated with excess lighting are algae overgrowth and overheating the water in smaller systems; otherwise, it is virtually impossible to have too much light in an aquarium system.4 A 12 hour photoperiod is considered appropriate for most fish. For those individuals interested in breeding fish, the photoperiod should be lengthened to mimic a spring/summer season.
Historically, aquarists have tended to ignore the substrate of an aquatic system, reducing it to a noninteracting element. In the aquaria of past decades, “clean,” relatively inert gravel and under-gravel filters were used to provide environments for all but the most specialized natural situations. In nature, with the exception of gravel bottoms in relatively unproductive hard rock mountain streams or sandy beaches with sandstone composition, rarely is the substrate material neutral. In most aquatic and marine environments, soft substrates are rich in organic reservoirs and harbor a myriad of important invertebrates and microbes that support rich plant growth. Limestone substrates control water chemistry, and reef corals and rocks determine the very character of the organisms growing on the surface of the reef. The interest in so-called live rock in coral reef tanks in recent years is beginning a tendency to replace sterile environments with live ecosystems. The addition of “trickle trays” with calcium carbonate pebbles also shows a developing interest in further elucidating the carbonate cycle and control over the pH. Conversely, acid, black water streams are most likely to occur in granite or sandstone areas where the natural acidity of the rain and tannic acid from the forest litter cannot be neutralized. To recreate this environment, the aquarist is advised to use hard rock and silica sand. Coarse sand or gravel is perhaps the most difficult of benthic environments for organisms to adapt to, and within sand and gravel habitats there are relatively few common species. In a stream or small lake that is not large enough for significant wave activity, or in a bay or coastal lagoon along a sandy coast, the sediment becomes progressively finer from gravel, to sand and silt, to a soupy, silty-clay mud substrate. To remain sand, the bottom must stay in constant motion; therefore, special adaptations are required by any organism to adapt to it. Even bacterial numbers tend to be limited in sand and gravel because their organic substrates are often washed out.9,10 It can be difficult to maintain a sandy, shore style substrate in a closed, captive system, as it can have a rather long profile in the energy regime required to maintain the sand. It would be impossible to recreate a wave-break, sandy scenario within a miniature system unless the benthic community is the only one desired.
Traditionally, the general approach to filtration followed by most aquarists was to avoid the natural detrital processes in an aquatic system and to keep bacteria in filters that mimicked the benthic community. However, in a filter, the variety, density, and capability of the bacteria are limited. Thus, aquarium procedures of the past have tended to short-circuit the natural cycling processes, which resulted in the loss of valuable energy to the many members of the community. Aquaria that do not have a fine sediment component should have a separate sediment trap that can be partially drained of sediment, especially if it is intended to drive a system faster than normal for scaling. For the aquarist, fine sediment bottoms should not be ignored. Given their full reign, with the proper environment and biota available, they can be important buffering systems and provide necessary stability for a healthy environment.
There are a myriad of commercial accessories available for aquaria today. These accessories range from simple items, such as heaters and aeration devices, to some of the most advanced biotechnology available in the field, such as chillers and wave machines. Most commercial accessories available on the market are well made, and the deficiencies have been minimized over the years. When choosing a particular item, selection should be based on function not brand. For example, with a heater, it is important to match the wattage of the instrument to the volume of water to be heated, taking into account the general temperature required for the environment in which the aquarium is to be located.4 There are several types of heaters available, including basic submersible heating elements, solar units, flow through units, or a combination of similar systems.
Water filtration units should be selected based on desired type of filtration, the volume requirements of a particular system, and its intended use. For example, a sand filtration unit should be selected on the basis of the volume of water to be used, the turnover rate expected for that volume of water, and the frequency with which the sand filter must be backwashed. Sometimes it is preferable, if not necessary, to combine several methods of filtration (e.g., under-gravel filtration in combination with sand filtration and power filtration). This enables the water to be “cleaned” using multiple methods. The use of multiple filters inline is particularly important in a public facility where a large water volume and bioload are used.
Most saltwater aquaria utilize some form of ozonator in combination with a protein skimmer. Protein skimmers utilize the age-old technology that has been used by sewage treatment plants for years: Minute air bubbles are passed through water with a high organic waste content, and the protein is captured and trapped as foam at the surface of the water. The greater the degree of organic pollution there is, the more stable the foam will be. The skimmer collects the foam, and the foam is then collapsed to a liquid and removed from the aquarium without tainting the water.
The aquatic environment is a very complex system that is subject to constant physical and chemical changes. A water-assessment program should be devised for monitoring an aquatic ecosystem. Many factors need to be taken into consideration when designing a water quality monitoring program, including the volume of water in the aquarium/aquaria, the number and type of animals that will be present, the type of life support system, and the period of time the aquarium has been set up. Ideally, a water-assessment program should be established before designing and setting up a system, keeping in mind that most of the water quality analysis is done to keep its inhabitants healthy.8
Water testing should be done daily for new aquaria until the system has cycled. When collecting a water sample, it is important to collect a mid-water sample, as samples closer to the surface or substrate will reflect more extreme values.2,3 Portable water analysis kits use premeasured reagents and simple analytic methods that may compromise the degree of accuracy. However, they are suitable for most private aquarists and small backyard ponds. Most large, public aquaria use more advanced analytic methods, such as mass spectrometry, saturometers, and sophisticated chemical analysis, for evaluating water quality. The acquisition and utilization of many of these processes and techniques are beyond the scope of what most private aquarists can afford. Commercial water quality laboratories can perform a complete water analysis for a modest price, and it may be a good idea to submit a sample to a laboratory for a baseline measurement. This method also offers the added benefit of comparing standardized values with the parameters derived from veterinarians’ own testing methods.
Water quality is very important to the health of a fish, and poor water quality can prove fatal. There are two types of systems that can be used: open and closed. In open water systems, the water in the aquarium is continually replenished using a fresh water source. An individual who lives near the ocean may collect seawater for a home aquarium, although that is not recommended because of potential contaminants in the water. Open water systems are rarely used because they are labor intensive and require regular exchange of the entire system. The majority of home aquaria utilize closed recirculating systems, which recirculate the same water over and over again using a filter. In the closed system, fresh water is added only after evaporation or at the time of a water change.
Ammonia is produced in fish as an end product of protein catabolism. This waste product is primarily excreted via the gills, although some excretion in the feces also occurs. Ammonia is also generated in the aquatic system from the breakdown of uneaten food and detritus. Ammonia nitrogen can occur in two forms: ammonium (NH4+) and ammonia (NH3). Ammonia is the more toxic form for fish.11 The relative concentration of each form varies with pH and water temperature.12 Ammonia is soluble in water, and minimal amounts are lost through evaporation. In a closed system, such as an aquarium or backyard pond, ammonia levels can build up to toxic quantities (>1 ppm). Even low levels of ammonia can be toxic to the gills and skin, resulting in increased susceptibility to infections. Fish suffering from ammonia toxicity appear irritated, gasp at the water’s surface, and rub against rocks in the aquarium as a result of the irritation caused by the toxin. Ammonia levels should be monitored closely in closed systems, especially those with high fish densities. Testing for ammonia should be done weekly using a standardized commercial test kit, which is available at local pet retailers. In an established system, ammonia levels should be zero. If the ammonia levels begin to rise, then the system should be reevaluated. Overfeeding and overstocking an aquarium can overburden the biologic filter. Severe temperature fluctuations and insufficient oxygen levels may also result in a significant loss of the biologic filter. This is especially common in ponds that have significant summer algal blooms. New systems require time to become established, and new fish should be added gradually to prevent an overload of the biologic filter.
Because ammonia is a common waste product in the aquarium, most problems can be prevented by limiting the numbers of fish in the aquarium and regulating the amount of feed being offered. A general rule of thumb for feeding fish is to only offer what they can eat in a 2- to 5-minute period. In cases where ammonia levels are creating problems, the first recommendation is to remove 25% to 50% of the water from the system and replace it with fresh, dechlorinated water. There are commercial products available that can chelate the ammonia source, but they are only a temporary solution. The primary cause of the elevated ammonia levels must be diagnosed and corrected.
Ammonia is a colorless, odorless substance that can cause significant mortalities in a home aquarium. Most inex-perienced aquarists tend to single out infectious diseases when they experience fish losses; however, poor water quality (e.g., excessive ammonia or nitrite) is often a primary/secondary cause of mortalities in these animals and should be tested on a regular basis.
The nitrogen cycle eliminates ammonia by converting it to less toxic compounds. The first step in the cycle is to convert ammonia to nitrite. Nitrosomonas spp. are the primary bacteria associated with this process. Unfortunately, nitrite is also toxic (>0.1 ppm) to fish and can be rapidly absorbed across the gills. Affected animals may develop a methemoglobinemia and have a characteristic “brown blood.” This blood dyscrasia leads to reduced erythrocyte oxygenation and respiratory compromise. Fish with nitrite toxicity may behave similarly to fish with ammonia toxicity, and be found gasping for air at the water surface and die suddenly. When fish show clinical signs associated with nitrite toxicity, they should be removed from the toxic water and placed into a fresh, dechlorinated, well-oxygenated system. A significant water change (25%-50%) should be made in the original aquarium or pond and the biologic filter reestablished. Salt can also be used to diminish the toxicity associated with salt.
The second step of the nitrogen cycle occurs when Nitrobacter spp. oxidizes nitrite to nitrate. Nitrate levels less than 0.5 ppm are generally regarded as safe; levels less than 5.0 ppm are associated with stress and may predispose fish to opportunistic infections; levels greater than 10 ppm are considered toxic for some species. Reports of nitrate toxicity are rare in freshwater and saltwater fish, but at elevated levels they may be stressful and predispose the animals to opportunistic pathogens. Nitrate is utilized by plants and algae as a food source. Nitrate can be removed from an aquatic system by performing regular water changes.
Ammonia and nitrite levels in an aquatic system may rise soon after treatment of the water with antibacterial compounds or a reduction in water temperature. Antibiotics added to the water are nonselective and may kill both pathogenic and commensal organisms. If these compounds kill enough of the bacteria associated with the biologic filter, then oxidation of ammonia and nitrite may stop. Nitrosomonas spp. are more temperature tolerant and will recolonize before Nitrobacter spp., so ammonia levels should be expected to decrease before nitrites. Therefore, elevated nitrite levels are often detected soon after a reduction in water temperature.
“New tank” syndrome is a common occurrence with beginner aquarists and primarily occurs when fish are overstocked in a new aquarium. If large numbers of fish are added to an aquarium, and the biologic filter is not established, the system will be unable to eliminate the ammonia produced by the fish. In most cases, the owners report an acute mortality event with clinical signs consistent with ammonia and nitrite toxicity. These problems can be prevented if the new owner is patient and realizes the importance of providing a break-in for the filter (4-6 weeks). Fish should be stocked gradually, usually one to two fish per week. A standard rule of thumb for a freshwater stocking density is 1 to 1.5 inches of fish per gallon of water; in saltwater systems, the stocking density should be 2 to 2.5 inches of fish per gallon of water. With the advent of new filtration systems, stocking densities will continue to increase; however, if the filter becomes compromised or fails, the results would be disastrous.
In the aquatic system, oxygen diffuses into water at the surface when the surface tension of the water is broken. For home aquaria, this occurs regularly when external filters are used that “drop” the water back into the tank like a waterfall or when airstones are used. The amount of available or dissolved oxygen (DO) within the system can be measured using special equipment. In most cases, a DO greater than 5 ppm is sufficient to maintain fish. For the home hobbyist, oxygen depletion is generally only a major problem with outdoor ponds during the summer months. During the day, plants produce their own food (photosynthesis) by removing carbon dioxide from the water and using energy produced by the sun. As plants make their food, they release oxygen into the water. During the night when plants or algae cannot undergo photosynthesis, they actually consume oxygen. In ponds with a large number of plants or algae, the oxygen levels in the water can fall to dangerously low levels (<3 ppm) for the fish. Another factor that may affect oxygen levels in the water column is temperature. Oxygen is lost to the atmosphere more rapidly in warm water than cold water. The use of aerators or fountains, especially at night, will help maintain adequate levels of oxygen in a pond.
The pH of water is measured by taking the negative logarithm of hydrogen ions in the water. In simplest terms, pH can de divided into three categories: acid, neutral, and basic. The range of pH values fits on a scale of 1 to 14. Values below 7.0 represent acidic water, values between 7.0 and 7.9 are neutral, and values above 8.0 are basic. The pH in most aquaria and ponds should fall between 6.5 and 8.5. In the extreme ranges (<4.0 or >10.0), water would be so acidic or basic that it would burn the fish. This means that the difference between 7.0 and 8.0 is much more significant than expected, because the pH values are based on a logarithmic scale. Therefore, if the pH is allowed to fluctuate, fish will become stressed and more susceptible to disease. The pH of natural bodies of water varies based on the substrate, water shed, and other environmental factors. Fish from Central America and South America thrive in water that is neutral or slightly acidic, whereas fish from Africa and Asia thrive better at neutral to alkaline water.
Water should always be tested before replacement into an aquarium. There are a number of factors that may affect the pH in an aquarium or pond, including the biologic filter, fish density, vegetation, and algae. Biologic filtration actually produces acid when ammonia is converted into nitrite. If the water has a low buffering capacity, and the aquarium or pond biologic filter is converting a large amount of ammonia, the pH could become very acidic. Fish produce carbon dioxide (CO2) as a waste product. When an aquarium or pond is heavily stocked with fish, the amount of CO2 can build up in the water. Carbon dioxide promotes acid production and can actually decrease the pH (acidic). Plants and algae, which use photosynthesis during the day to make energy, utilize CO2. However, at night, plants and algae utilize oxygen (like fish) and expel CO2 as a waste product. In a system with a large number of plants and a large amount of algae, the pH can drop to a dangerously low level. Fish die-offs in ponds are often associated with high CO2, low pH, and low oxygen levels. When plants or fish die, they also release compounds that can lower the pH. To prevent this from becoming a problem, always immediately remove dead fish or plants.
Chlorine is an elemental gas that is added to municipal water as a disinfectant. Unfortunately, chlorine is also toxic to fish. Fish that are exposed to chlorinated water can develop life-threatening respiratory distress. Chlorine readily crosses the gills of fish and blocks the animal’s ability to absorb oxygen. Fortunately, chlorine can be removed from the water by allowing it to de-gas for 48 to 72 hours or by adding a dechlorinator (e.g., sodium thiosulfate). Chlorine levels in municipal water can fluctuate with the season; thus, questions about the timing or the amounts of chlorine that are being added in a specific municipality should be directed to the local water company. Chlorine levels in a water sample can be tested using a commercial test kit purchased from a local pet retailer.
Chloramine represents another disinfectant that is routinely added to municipal water for sterilization purposes. Chloramines are a combination of chlorine and ammonia. Commercial dechlorinators can still be used to remove the chlorine from this molecule, but they do nothing to the ammonia. Because ammonia is toxic to fish, it is important that levels of this compound do not reach levels greater than 1 ppm. Fortunately, a functional biologic filter will prevent this from occurring.
Hardness measures the quantity of divalent cations (e.g., calcium and magnesium) in the water. In natural waters, the divalent ions are derived from the limestone, salts, and soils. The general range for hardness in freshwater systems is 0 to 250 mg/L, whereas in saltwater systems, hardness can exceed 10,000 mg/L.13 The divalent cations that represent hardness, calcium and magnesium, play an intricate role in water quality conditions. Calcium can alter osmoregulatory function in fish during times of low pH or elevated ammonia.13 Calcium and magnesium are both important for growth and development in fish fry.14 These minerals can also protect fish against heavy metals by competing for gill absorption sites. Copper is routinely used to treat parasites. Calcium and magnesium compete with the copper for absorption sites, reducing the effectiveness of the copper. Distilled water should never be used to replenish water in an aquarium because it is deficient in these essential cations.
In natural aquatic systems (e.g., lakes, ponds, rivers, streams), fish are exposed to a relatively stable pH because of buffers. The most common buffers in aquatic systems are bicarbonate (HCO3) and carbonate (CO32−). Other buffers that may occur in water in lesser amounts include hydroxide (OH−), silicates, phosphates, and borates. The quantity of buffers within a system depends upon the source of the water. Some municipal water supplies contain relatively low concentrations of buffers, whereas others may have large concentrations. In cases where the water has a low buffering capacity, commercial buffers can be purchased from a local pet store and added to an aquarium to create a more stable pH.
Total alkalinity can also play a protective role against potential heavy metal toxins. Heavy metals (e.g., copper and lead) in the water can be absorbed at the level of the gills, build up to toxic levels, and lead to the eventual death of an affected fish. Bicarbonate and carbonate can protect against heavy metals by chelating them in the water, rendering them harmless. This is important to remember when treating fish with nonchelated copper. If the alkalinity is high, the nonchelated copper may be bound and rendered useless.