and koi

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:

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.

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.

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:


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.

Anaesthetic protocol for fish anaesthesia

Skin disorders

Differential diagnoses for skin disorders

Nodules and non-healing wounds

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)

Treatment/specific therapy

Aug 21, 2016 | Posted by in EXOTIC, WILD, ZOO | Comments Off on and koi

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