Practical Approach to the Fish Case

VETcpd - Exotics: Fish Peer Reviewed Practical approach to the fi sh case Veterinary surgeons will get calls about fi sh occasionally, and the veterinary surgeon should be in a position to offer some help. This article will discuss the basics of the approach to a fi sh veterinary case. As with all veterinary patients, always consider how you can minimise stress to the fi sh. Key words: fi sh, veterinary approach, water quality, husbandry, disease, treatment Bruce Maclean Introduction BSc(VetSci) BVM&S MRCVS A very large part of keeping fi sh quite toxic, and further by (diff erent) Bruce Maclean graduated from the successfully is maintaining good water microorganisms to nitrate, which is much Royal Dick (Edinburgh) vet school in quality, and much of the accessory less toxic. This may then be taken up by 1992. Following graduation, he spent equipment used by fi shkeepers (fi lters, plants, which are re-ingested (directly or time in the Avian and Exotic department aeration, protein skimmers and so on) is indirectly via invertebrates) by the fi sh. at Utrecht University further studying devoted to this (Figure 1). the veterinary care of birds and exotic The primary function of the fi lter is to animals. As a veterinary surgeon, you need to be aid this process - physical straining of the On return to the UK, Bruce spent 6 at least aware of this and how it can water is generally a minor part of the months in mixed practice and a short impact the health of the fi sh. Any water fi lter’s role. The fi lter medium essentially period in small animal/exotics practice. quality issues will be directly toxic or provides a very large surface area for the He then set up his own dedicated cause the fi sh stress, predisposing them growth of the various microorganisms. birds/exotics practice and has been to health problems. This is of clinical signifi cance in that working exclusively with birds and exotic animals, both fi rst opinion if these microorganisms are wiped out and referral, since then. Bruce has or severely reduced, either by water contributed chapters to BSAVA manuals treatments (including antibiotics), or by and several articles in UK and US overzealous cleaning, the system is likely based veterinary publications. to “crash” with a dramatic ammonia spike. Bruce has been keeping reptiles and These microorganisms need to build up amphibians for 40 + years, and over time, and a fi lter can take weeks to amphibian, invertebrate and seahorse months to fully mature. With this in mind medicine are particular clinical the stocking density of fi sh needs to be interests. built up gradually to avoid ‘new tank HerpVet Services, c/o Iffl ey Vets syndrome’, where the initial stocking level 35 Iffl ey Road, Oxford OX4 1EA is too high for the state of the fi ltration. E-mail: [email protected] Tel: 07754 125302 A key point is that ammonia is the most toxic form of nitrogenous waste. Toxicity is related to the level of ionisation with NH3 being more toxic than NH4+. Ionisation is aff ected by water pH and temperature, with more toxic NH3 produced at higher temperatures and pH. Figure 1: Fish tank (right) with separate fi lter tank (left) Nitrite is still relatively toxic while nitrate is much less so. Fish will vary somewhat Water parameters in tolerance, but essentially on water tests, Exotic referrals: and the nitrogen cycle ammonia and nitrite should be 0, whilst vetindex.co.uk/exotics up to 40 mg/L (ppm) nitrate is acceptable An understanding of the nitrogen cycle is for most fi sh. Exotic Animal Health Products: fundamental to keeping fi sh. Essentially fi sh vetindex.co.uk/exotic-products produce nitrogenous waste in the form Market your referrals in VetIndex! of ammonia, which is highly toxic. This is Other parameters For further information call us on broken down by various environmental Other important parameters that must be 01225 445561 or email: [email protected] microorganisms to nitrite, which is still monitored include pH, hardness and oxygen. Page 14 - VETcpd - Vol 3 - Issue 3 Table 1: Water parameters Parameter Safe level Source Notes pH Ammonia The pH is important directly, in that fish 0 mg/L Produced by metabolism More toxic at higher pH, (also organic matter higher temperature will have optimum levels for that species, breakdown) Excess causes increased outside which they will suffer varying respiration, lethargy, degrees of stress. It also affects the filter anorexia, death bacteria; a pH fall below about five will kill the filter bacteria, causing a system Nitrite 0 mg/L Produced from ammonia Binds haemoglobin so primarily ammonia spike. Heavy plant growth can by filter bacteria respiratory signs (increased respiration/dyspnoea) affect pH through the day, depending on buffering capacity of the water. Nitrate < 40 mg/L Produced from nitrite by Excess causes chronic stress/ filter bacteria immunosuppression Hardness Hardness refers to various cations, mostly pH Varies with Inappropriate value for fish calcium and magnesium, and is a measure species; will cause stress, skin/gill normally 6.5 - 8 irritation; sensitivity varies of buffering capacity which resists pH with species. changes. Various scales of measurement are Buffering capacity of water is used. Again, individual species will have important; rapid pH changes tolerated and preferred ranges of hardness. stress fish, and may even kill the filter bacteria Oxygen Oxygen dissolves from the air, aided by Oxygen > 5 mg/L Gas exchange with air Warmer water holds less (improved by aeration via oxygen water flows and aeration devices, and is airstones, water flow); Large fish more affected also produced by any live plants in the plant photosynthesis (but Note formalin reduces tank or pond. However, it is important to note plants net use oxygen dissolved oxygen remember that plants, whilst net producers at night; water O2 levels of oxygen during the day, are net users lowest in early morning) during the night. The lowest oxygen levels Hardness Depends on Cations in water Important for buffering in a planted tank or pond are just before species (Ca, Mg) capacity of water; if depleted, dawn, which is also when any samples pH drop and resulting filter should be taken if possible. Also note that crash possible (“old tank syndrome”) the warmer the water, the less oxygen it can hold. Mortalities always overnight, Copper Variable with Medication, Used as a medication, but in a well-planted pond in summer, are species; algae treatment has narrow therapeutic index classically a sign of oxygen deficiency invertebrates and problems, either primary or secondary corals generally very susceptible (e.g. to gill disease). Iron 0 mg/L Other parameters such as phosphate, iron, zinc and copper may be checked in specific Zinc 0 mg/L cases. In marine tanks, particularly those with live coral (Figure 2), many trace Trace elements Salt mix used to make Sometimes important to minerals are also important. See Table 1 artificial seawater marine set-ups including for more details on water parameters. corals; little known about significance to fish Salinity (marine) Fish vary in Specific gravity often used as /specific gravity tolerance of salinity surrogate measure of salinity variation, but rapid changes (e.g. with different batch of saltwater) will cause electrolyte balance issues Chlorine Species will vary in Routinely present in Not routinely tested, but tolerance tapwater essentially tapwater must be treated (usually with suitable water treatment) before use with fish to remove chlorine. Excess causes acute dyspnoea and mortalities Figure 2: Fish with corals – note the corals may Table 1: Differing fish species and individuals will have differing tolerances of these parameters, be more important to the owner than the fish, and effect of parameters may vary depending on one another. Speed of any change may be a factor. which can complicate treatment The safe level listed is only a guideline Full article available for purchase at www.vetcpd.co.uk/modules/ VETcpd - Vol 3 - Issue 3 - Page 15.

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