Keeping pet fish: common pitfalls and how vets can support clients

Transcription

1 Vet Times The website for the veterinary profession Keeping pet fish: common pitfalls and how vets can support clients Author : Paul Imrie Categories : Exotics, General, Vets Date : May 23, 2016 Each year, the Pet Food Manufacturers Association commissions the Pet Population report, which looks in detail at pet ownership trends. This year, it is estimated 11 million (40%) households have pets. The pet population stands at around 57 million of which 36 million are pet fish, compared with 8.5 million dogs and 7.5 million cats. Table 1. Water requirements for commonly kept fish species. Vets need to support fish owners to improve the welfare and decrease the mortality seen in this species through poor knowledge. More fish owners are approaching vets for advice, support and care of their sick fish. This article provides a basic approach to fish medicine, covering common pitfalls of freshwater aquarium fish keeping. Husbandry Poor husbandry is one of the most common causes of disease in fish. Problems relating to water 1 / 11

2 quality (poor hygiene, toxin build-up), temperature, diet and tank size are similar to those seen with other exotic animals. The approach to history taking is also similar, as a detailed history can provide the vet with a logical approach for further investigation and management of the problems and diseases. Water quality The water requirements for commonly kept fish are shown in Table 1. ph and ammonia 2 / 11

3 3 / 11

4 Figures 1a (top) and 1b. Regular (at least monthly) measurement of ammonia and ph will help prompt an increased water change requirement and investigation of the primary cause of the change. Most freshwater aquarium fish tolerate a ph value of ph6 to ph8. The African dwarf cichlid (Neolamprologus and Julidochromis) is the exception, as it prefers a more alkaline environment. Fish may survive outside of their preferred optimum ph, but will be stressed, immunosuppressed and their growth rate reduced. A small change on the ph scale reflects a large change in acidity, as the ph scale is logarithmic. ph changes should be buffered with an agent, such as calcium carbonate. Soft water has less buffering agents than hard water and should be supplemented with calcium carbonate to prevent dramatic shifts in ph. Regular (at least monthly) measurement of ammonia and ph will help prompt an increase water change requirement and investigation of the primary cause of the change (Figures 1a and 1b). Causes of ph dropping (acidity increased): Chlorine in tap water is acidic. Dechlorinating agents should be used, or clean, fresh, rain water should be used for weekly water changes. Carbon dioxide forms carbonic acid. This builds up in a sealed bag during transport. Oversupplementation of carbon dioxide used in some planted aquaria can also be a source. The diurnal rhythm of a well-planted tank will produce more carbon dioxide at night. Some drugs, such as tricaine methanesulfonate anaesthetic, is acidic and must be buffered before use. The nitrogen cycle (Figure 2) is essential to break down ammonia the main waste 4 / 11

5 product of fish protein metabolism, which is excreted by the gills and kidneys as urine. Decomposing food, plants and dead fish are other important sources of ammonia. One of the breakdown products is nitrates, which is acidifying. Regular water changes (10% weekly, or 25% to 30% every two weeks) are essential to remove a build of nitrates. Causes of rising ph: Ammonia from fish waste and detritus is alkaline. Ideally, the biological filter will contain friendly bacteria, such as Nitrosomonas, Nitrobacter and other microorganisms, which break down ammonia to nitrite in the nitrogen cycle (Figure 2). In tanks with no biological filter, a low population of friendly bacteria may colonise the water, surfaces of substrate and tank decorations. If the tank has an insufficient population of friendly bacteria for the amount of fish or detritus in the tank then ammonia levels rise. Chlorine, high levels of ammonia, poor water oxygenation, antibiotics, overzealous filter cleaning or a blocked filter all inhibit nitrobacteria growth. Care of these friendly bacteria, the other pet in the tank, will help keep the fish healthy. Hardness The mineral salt levels of water are often expressed as hard water or soft water. A water hardness level less than 50mg/L, 3 degrees of hardness (dh), is called soft water and more than 300mg/L (18dH) is called hard water. The preferred water hardness for most fish is 50mg/L to 400mg/L (3dH to 22dH). A level above 100mg/L (5.5dH) ensures sufficient buffering agents are in the water. Table 1 shows the preferred hardness level for commonly kept fish. Fish have to actively pump water molecules out of their body, which have entered their tissues by osmosis, to maintain their water balance. The harder the water, the less they have to pump out. Extremely hard water contains a lot of calcium and magnesium salts, which can cause renal calculi and nephrocalcinosis. Soft water has less buffering agents so rapid changes in ph of the water may cause problems for the fish. Oxygen Dissolved oxygen is absorbed through the gills of the fish. Hypoxia is fatal. Oxygen dissolves into the water through the surface by diffusion. Water changes, or top-ups, are the most efficient way of adding oxygenated water to the tank. Causes of hypoxia: Oil, protein, dust, food and excessive surface plant growth reduce the surface area available for gas exchange. 5 / 11

6 Increased water temperature decreases the solubility of oxygen and increases the biological oxygen demand of the fish, plants and bacteria living in the tank. Salinity reduces the solubility of oxygen. Causes of supersaturation of oxygen: Rare in a tank, but lots of plants or algae and artificial light or sunlight produce excessive levels of oxygen, which may cause gas bubble disease in some fish. 6 / 11

7 Figure 2. The nitrogen cycle is an essential cycle of breakdown of fish waste and tank detritus by the friendly bacteria the other pet in the tank. Table 2. Expected lifespan and adult size of commonly kept fish. 7 / 11

8 Figure 3. A neon tetra (Paracheirodon innesi) gulping at the water surface. This is a clinical sign of hypoxia. A common cause is ammonia toxicity in a new tank syndrome. Water toxins Tap water contains chlorine and chloramine, which are toxic to fish. Chlorine can be removed by the addition of commercial chemical dechlorinating agents (but are not always reliable), the addition of sodium thiosulphate or being left to stand in an open bucket for 24 hours. Clean, fresh rainwater or bottled water (without chlorine) could be used as an alternative. Nitrite, nitrate and ammonia are toxic to fish. Ammonia causes gill damage and signs of hypoxia, such as gulping for air at the surface, may be seen (Figure 3). Copper, iron and lead may be found in water supplies leaching out of metal pipes or gutters and are toxic to fish. The lethal copper level for fish is species-dependent. Copper is a common pesticide and used in ectoparasitic treatments. Most disinfectants, aerosol sprays (including household flea sprays), hand gels or creams and other chemicals may enter the tank by air or on the hands of the owner during routine tank maintenance. These pollutants are often harmful to the fish. Temperature 8 / 11

9 Figure 4. Fish showing white spot or ich (Ichthyophthirius multifiliis). This ciliate parasite commonly affects stressed fish. The primary cause of the stress must also be addressed, as well as specific treatment of this parasite. Like other ectothermic exotic pets (reptiles), fish are dependent on the environmental temperature for enzyme activity and metabolic rate. Aquarium fish can be classified as those that can live in an unheated aquarium (cold water fish) and those that need a heater to maintain the water above room temperature (tropical fish). Table 1 shows the preferred optimum water temperature for commonly kept cold water and tropical aquarium fish. The heater should have a thermostat and both need to be completely submerged to prevent overheating the water. Lower water temperatures reduce the toxicity of ammonia. Rapid temperature changes are not well-tolerated and may cause stress (Figure 4) and immunosuppression. Gradual changes by a few degrees Celsius are acceptable. Lighting Fish do not require artificial light; however, due to photosynthesis, it is essential for an aquarium with live plants. Fish will get stressed if artificial light (aquarium light or room light) is provided for 24 hours. A regular period of darkness of 8 hours to 12 hours is recommended. Diet Over-feeding and then a build-up of detritus with an increase in ammonia is a common problem. Fish should only be fed a maximum amount of food they can eat in two minutes to three minutes twice daily. Fish can cope with being fed less frequently (twice a week), provided they are otherwise well. A varied diet is appropriate to avoid nutritional deficiencies. An appropriate diet of floating flakes or pellets for surface feeders, sinking pellets for bottom feeders (catfish), fresh salad and live insects are all important. If the fish are very small, the food may need to be crushed. 9 / 11

10 Common pitfalls New tank syndrome A tank stocked too soon, or too quickly, before the friendly bacteria have colonised sufficiently to cope with the amount of waste produced by the fish, results in lethal levels of ammonia. This causes mass morbidity (gill damage and hypoxia) and mortality within days of the fish being added to the tank. The tank should be set up and the filter allowed to run for six weeks before any fish are added to the system. Probiotics may be added to help development of friendly bacteria, although a source of ammonia is required. Table 3. Fish behaviour. Gradual stocking is essential. Initially, one fish to three fish should be added to the tank (depending on tank size) and the filter allowed to mature for at least six weeks before more fish are added. A maximum of two fish to three fish should then be introduced every two weeks to four weeks, depending on the size of the tank. Regular weekly or biweekly removal of 10% to 20% of the tank 10 / 11

11 Powered by TCPDF ( water and replacement of dechlorinated water will reduce the ammonia and, later, nitrite build-up until the friendly bacteria population has increased. Old tank syndrome Poor tank hygiene and failure to stir the substrate regularly leads to a build-up of anaerobic bacteria, which produce hydrogen sulphide toxic to fish. Overstocking The maximum stocking density of a tank is related to the water surface area available for oxygen diffusion. The adult fish lengths are given in Table 2. The general accepted rule for goldfish is 144cm 2 water surface area for every 2.5cm of fish length (excluding tail fin). For tropical fish, 72cm 2 water surface area for every 2.5cm of fish length is required. Successful rearing of fish fry can lead to an originally well-stocked tank becoming overstocked (Table 3). Overstocking will lead to high levels of fish waste being produced and insufficient oxygen levels. Over-the-counter medications are commonly used by owners, either prophylactically or as a treatment. However, as the primary cause (often water quality issues) has not been addressed or primary disease undiagnosed, this is often unsuccessful and leads to a delay in seeking veterinary advice. These treatments often have harmful effects on the friendly bacteria in the tank. Overzealous cleaning Cleaning the tank equipment especially the filter with chlorinated water, hot water or any disinfectants is likely to destroy the friendly bacteria and, therefore, lead to ammonia poisoning of the fish. Water removed during a water change is good for gentle cleaning of the filter. Hot tap water can be used to clean nets and tank equipment, but should be left to air dry. 11 / 11