Chapter 11 Goldfish and koi

This chapter covers those disorders likely to be seen in goldfish and koi, which constitute the most popular section of fish-keeping. Tolerance of wide temperature ranges means that these species can be kept outside, as well as inside, in most temperate countries such as Europe and North America. However, they are also happy at more tropical temperatures and in those countries such as Singapore, Malaysia and southern China where they are kept alongside ‘tropical species’. Hence, this disorders chapter should be read in conjunction with that on Tropical Freshwater Fish.

Fish-keeping is a huge worldwide hobby and industry. Unfortunately, veterinarians are often last to be consulted over a fish-related problem, or else they are approached purely as a source of antibiotics and other regulated medications. This is because:

1 There are a great many proprietary products available for the treatment of ornamental fish, which aquarists are able to access from their aquarium retailer without recourse to the veterinarian. Most of these products are poorly regulated and, therefore, their efficacy is often very poor in contrast to the claims made for them; a problem compounded by inadequate diagnostics by both aquarist and helpful retailer. Ectoparasitic preparations are usually sufficiently efficacious to justify their use when their safety and ease of use is also brought into consideration.

2 This ready availability of proprietary medications devalues professional input.

3 There is a low economic cost for many widely kept fish.

4 There is a historical perception that veterinarians know little about fish and fish diseases.

Consultation and handling

The key to successful fish-keeping, and a major stumbling point, is water quality. Recommended water-quality parameters for koi and goldfish are listed in Table 11.1.

Table 11.1 Recommended water quality parameters for koi and goldfish

Parameter	Value
Temperature (°C)	10–30 (preferred range = 22–28 for Koi)
pH	6.0–8.4 (preferred 7.0–8.0)
Hardness (CaCO₃) (mg/L)	100–250
Conductivity (mS/cm)	180–480
Ammonia (total) (mg/L)	<0.02
Nitrite (mg/L)	<0.2
Nitrate (above ambient tapwater levels) (mg/L)	<40
Oxygen (mg/L)	5.0–8.0
Chlorine (mg/L)	0.002

Adapted from Jepson (2001).

Hobbyist test kits are available to measure these parameters and they give reasonable results; accurate testing requires professional equipment.

If possible, fish should be examined in their home aquarium or pond. However, if the pond is large it may pay to ask for the fish to be caught and separated before arrival, as much time can be wasted attempting to catch the fish. Ponds are rarely built with recapture in mind. Once caught, place the fish on a damp towel for examination. If necessary sedate with MS222 or benzocaine (see ‘Anaesthesia’, below).

Always examine the ventral surface, as lesions here may not be obvious when viewed from above. Skin scrapes should be taken from the operculae, the flank, and around the base of the fins. Examine the gills and oral cavity.

Blood sampling

This is best done under anaesthesia (see below). Blood can be drawn using a well-heparinized syringe from the ventral tail vein, which runs midline just below the caudal vertebrae. In small fish this can be accessed via the ventral midline while in larger fish, a lateral approach is often better. This same approach can be used for intravenous injections.

For the internal anatomy of a goldfish, see Figure 11.1.

Fig. 11.1 Internal anatomy of goldfish. Note that goldfish and koi do not possess a true stomach. Adhesions between the internal organs are normal and not the result of coelomitis.

Nursing care

Provision of optimal water quality is essential to maximize recovery. A separate hospital aquarium or vat can be used but the water quality in this facility should be as good as in a main display (Fig. 11.2). The water should be filtered, but because of the use of medications such as antibiotics, biological filtration cannot be used. After each patient, the aquarium or vat should be dismantled and cleaned out with an iodine-based disinfectant.

Fig. 11.2 Clinical aquarium setup.

Reliance is placed upon physical and chemical methods of water purification. Zeolite will absorb ammonia excreted by the fish, while activated charcoal will adsorb many harmful chemicals from the water. If salt is used, a small protein skimmer would be of great benefit. Ozonizers and ultraviolet sterilization are also useful adjuncts. Keep decorations to a minimum, giving just sufficient for nervous fish to hide behind. All materials used should be readily cleanable, such as plastic – and avoid live plants and bogwood where possible, as these can act as disease reservoirs. Temperature can be maintained at the optimum using commercial aquarium heaters. For koi and goldfish, a temperature of 18–25 °C should be considered. Keeping fish in a permanent 5 g/L solution of salt (use aquarium or sea salt, not table or rock salt) will reduce the osmotic load on a sick koi or goldfish.

Antibiotics can be administered either by:

1 Injection. Optimum site is either immediately in front or behind the dorsal fin in the midline

2 In feed (but note that many sick fish are inappetant)

3 Bath (may damage biological filtration)

4 Gavage.

Analgesia

Butorphanol at 0.05–0.5 mg/kg i.m.

Anaesthesia

There are a number of anaesthetic preparations and protocols described, but the author has found tricaine methane sulphonate and benzocaine to be the most useful.

Suitable anaesthetic agents

2 Benzocaine

a Must be dissolved in ethanol or acetone (stock solution of 100 g/L). Unstable in light. The author finds it less reliable than tricaine methane sulphonate, possibly due to effects of solute.

Anaesthetic protocol for fish anaesthesia

Maintenance

1 Fish can be maintained out of water for prolonged periods of time for surgery providing the gills are constantly bathed in oxygenated water. The simplest method is for an assistant to constantly and gently syringe water into the mouth such that it flows over the gills and out beneath the operculae. Water is selected from either the anaesthetic-containing or anaesthetic-free container as required.

2 For more advanced anaesthetic techniques, the fish can be placed over a water reservoir, with water continuously pumped from this reservoir and introduced into the oral cavity via a tube. The water exiting the operculae flows back into the reservoir below.

3 Anaesthesia is usually maintained at a concentration of tricaine methane sulphonate at 50–100 mg/L.

4 If performing multiple anaesthetics beware build up of ammonia and proteinaceous material from sloughed mucous.

5 During recovery, water flow over gills should be in physiologically normal direction as reversal short circuits normal counter current gaseous exchange mechanism.

Skin disorders

Skin structure

The skin is a large and complex organ that is constantly in contact with the immediate environment of the fish. Its functions include an osmotic barrier, disease barrier, protection, intra-specific signaling and camouflage. Histologically it consists of:

1 Cuticle. A thin mucopolysaccharide layer containing mucous, sloughed cells and antibodies

2 Epidermis. Stratified squamous epithelium plus mucous secreting cells

3 Dermis

a Stratum spongiosum. This contains chromatophores

b Scales (flat plates of bone) are also present in this layer

c Stratum compactum. This is a dense, collagenous tissue

4 Hypodermis. Loosely arranged, often vascular and may contain adipose tissue. Attaches integument to underlying muscle.

Note that the scales of fish are dermal structures (not epidermal thickenings as seen in reptiles), therefore the loss of scale involves damage to the overlying epidermis and a potential breach in the fishes’ immune and osmotic barrier.

Differential diagnoses for skin disorders

Pruritus

• Scratching against surfaces. Sometimes termed ‘flashing’ or ‘flicking’

• Ectoparasites

• Poor water quality.

Erosions and ulceration including fin rot

• Bacterial disease, typically Aeromonas spp, Cytophagic-like bacteria, Flavobacterium spp. Also mycobacteriosis (see Musculoskeletal Disorders). With Cytophaga psychrophila infection is often on the dorsal fin spreading towards the base where a large ulcer forms – this is sometime referred to as ‘saddle-back’ disease (Figs 11.3, 11.4)

• Fungal disease, such as Fusarium spp (see also Ophthalmic Disorders)

• Protozoa (Trichodina, Epistylis), Thelohanellus hovorkai (Yokohama et al 1999)

• Large ectoparasites, e.g. Argulus, Learnea

• Trauma with secondary bacterial infections. Often damage to skin and/or loss of eyes and fins. May occur due to predator attack, e.g. heron, raccoon, cat or during handling or spawning

• Sunburn. Will affect only the white or unpigmented areas of the dorsal surface.

Fig. 11.3 Bacterial ulceration in a koi.

Fig. 11.4 Mouth ulceration due to Flavobacteria.

Nodules and non-healing wounds

• Nuptial tubercles (normal in sexually mature goldfish and other cyprinids; usually confined to the operculae and leading rays of the pectoral fins. In some fancy goldfish, those on the fins can be very large and nodular, resembling neoplasia)

• Obvious discrete pin-head white spots (Ichthyophthirius multifilis). White spot disease. Also often breathing difficulties, irritation. Fins clamped

• Candle-wax masses on skin and fins on cyprinids, especially carp/koi. Retarded growth in young koi. Carp pox (cyprinid herpesvirus 1; CHV-1). Note may cause mass mortalities in young (2-week-old) carp (Sano et al 1991) (see Systemic Disorders)

• Dermocystidium koi (see also Musculoskeletal Disorders)

• Lymphocystis (iridovirus). Large, cauliflower like masses on fins and skin. Does not usually infect cyprinids, but may be seen in other pond or coldwater fish, e.g. sunfish (Lepomis spp)

• Epitheliocystis. Looks like lymphocystis but can infect cyprinids including carp

• Myxosporidae. Obvious nodules. Often fish displays dark or accentuating colouring, weight loss, whirling and fin rot

• Henneguya koi. Small, smooth rounded cyst-like nodules in the skin. Can also affect the gills and internal organs

• Wasting, darkening of skin colour and obvious boil-like swellings in the skin; in extreme cases it may have a sandpaper effect, due to the large number of granulomas present. Also exophthalmia, abnormal behaviour and swimming patterns (if the central nervous system is invaded). (Ichthyophonus hoferi). See also Neurological and Swimming Disorders, Ophthalmic Disorders and Systemic Disorders

• Gas filled bubbles in the skin especially on the fins. Also occasionally behind the eye (gas bubble disease – usually secondary to oxygen supersaturation)

• Hypersensitivity reactions at attachment sites of parasites such as Argulus and Lernea.

Changes in pigmentation or colour

• Reddened fin and skin. Bacterial infection (see ‘Erosions and ulceration’ above), golden shiner virus (Notemigonus crysoleucas only), spring viraemia of carp (SVC; see Systemic Disorders), grass carp rheovirus (Ctenopharygodon idella only)

• Greying skin (secondary to excessive mucous production) (ectoparasites esp. Chilonodella, Trichodina) (Fig. 11.5)

• White tufts on surface, may look like cotton wool (Epistylis, Saprolegnia, Cytophaga-like bacteria). In pond fish, fungal infections that have been present for some time may be green or brown due to secondary colonization by algae. Note that mucous strands hanging from the skin can strongly resemble Saprolegnia

• ‘Staff’s disease’ – Saprolegnia fungal growths present only in the nostrils. Seen in common carp in Poland during the winter months in 1–2 year old carp

• Obvious discrete white spots (Ichthyophirius). In koi, there is often a ‘salt and pepper’ dusting appearance rather than distinct white spots

• Dark or accentuating colouring (Myxosporidae)

• Dusty effect over body surface (Oodinium, velvet disease)

• Grey spots on gills and fins (Glocchidia – larval freshwater mussels)

• Whitish mucous tufts on hood (or wen) of fancy goldfish (see also Ophthalmic Disorders)

• Colour fading. In goldfish and koi it is likely to be a nutritional lack of appropriate carotenoids. Some goldfish on good diets do spontaneously turn white – this is likely to be genetic.

• Occasionally areas of dark pigment develop on the red areas of koi, particularly seen in kohakus. Known to koi-keepers as shimmies, these are merely changes in pigmentation and do not warrant removal except for aesthetic purposes.