Author name: mark.yan

Defining the concept of ‘health’ can be very tricky, generally, animals are considered ‘healthy’ if they are free from disease, however, disease is itself defined as a state of ill health!  These circular definitions can lead to confusion so perhaps a closer look at the causes of ill health in fish may help to hone any definition of health Causes of disease in fish can be categorised into 5 major groups, firstly, environmental causes; what fishkeepers would call ‘water quality’ problems. All fish have environmental requirements, they have a water temperature, pH and hardness range they prefer, and differing tolerances for various natural and exotic pollutants. If the environmental requirements are not met or pollution tolerances are exceeded, then disease occurs. The second type of disease is due to pathogens, infectious agents that can spread from fish to fish. Some are obligate pathogens that can only survive if there are susceptible fish around to infect, others are opportunistic, feeding happily on organic material in the water but switching to a pathogenic phase if the fish become susceptible. The link between environment and pathogen here is very intimate, fish that are weakened by adverse environmental conditions will become much more susceptible to these pathogens. Thus the aquarist who is battling ammonia and nitrite levels in his fish tank will soon encounter pathogenic disease such as the dreaded white spot parasite, Ichtyopthirius multifilis. Diseases of environmental origin are without doubt the most commonly encountered by aquatic professionals and hobbyists alike. Pathogenic disease often arises as a consequence; other causes of disease can be much more esoteric and less regularly encountered. An awareness is still vital to anyone with an interest in fish health and welfare. Many diseases can have their root in malnutrition, fish can be fed incorrect levels of proteins, fats or carbohydrates, but more commonly it is an imbalance of micronutrients such as vitamins and minerals that lie at the heart of the problem. The most commonly cited example is a deficiency of ascorbic acid – vitamin C, this antioxidant agent is vital for many biological functions not least collagen manufacture and many elements of immune system function. Fish show repeatable symptoms of deficiency if not enough is provided in the diet. Ensuring enough of this vitamin reaches the fish is complicated by the water soluble nature of the vitamin and its inherent instability in dry fish foods. Food manufacturers therefore add stabilised forms of vitamin at elevated levels to ensure the required amount reaches the fish. Avoiding food past it’s sell by date is a reliable way to avoid vitamin C deficiency in fish. Disease can also have its root at the genetic level; genes are sequences of the genetic material that code for specific proteins, these then form the builders and building blocks of the fish. Just as typographical errors can be made in a sentence, errors in the sequence of base chemicals in the genetic code lead to mistakes in the protein produced. These mutations are often harmless causing no visible or physiological effect in the fish; occasionally the error has a consequence. This can lead to disease in should this alteration of essential protein structure mean it is no longer be able to perform its role in the complex body system of the fish. We should also remember though that it is this mutation that gives us the infinite variety of life. As more research into fish behaviour and welfare is conducted, it is becoming more apparent that the psychological well being of the fish is just as crucial as good water quality, diet, genetics and the absence of pathogens. Aquarists have known for years that behaviour is a key player in fish health, fish stressed by aggressive attention from a socially dominant tankmate or breeding partner soon succumb to infectious disease. Even too much attention from humans (banging on the glass!), can weaken timid fish. However psychological well being extends much further than the fish not being bullied or scared. ‘Environmental enrichment’ is a hot topic among many animal husbandry professionals; this can be defined as the provision of environmental stimuli to encourage physical and mental activity. Examples of environmental enrichment in the ornamental fish world include target training Archer fish (Toxotes jaculatrix) or puzzle solving for a food reward in Common Octopus (Octopus vulgaris), more recently a goldfish training kit has become available to buy on the internet! At a much more simple level the provision of décor to offer cover, gravel or sand for benthic species, flow for riverine species or the correct spawning substrate would also be considered environmental enrichment, because these make the habitat more conducive to allowing the fish complete its natural behavioural repertoire. It is only through cutting edge welfare research involving monitoring stress markers such as catecholamine and corticosteroid hormones and endogenous opiods (natural pain relief chemicals), that the importance of the fish’s psychological well being will become apparent. So let’s return to our original definition of ‘health’ as an absence of disease. Disease symptoms are caused when the fish’s environmental requirements are not met, when pathogens infect, when the diet is incorrect, from a genetic origin or when the fish’s psychological needs are not met.  Thus when appraising the health of our fish we must consider all of these factors.

In order to recognise a poorly fish, we must first know what a fish looks like and how it behaves when healthy. We can only recognise the ‘abnormal’ when we know what is normal. For example, a goldfish keeper may become concerned about the presence of small white spots on the gill covers and pectoral fins of their fish. Further investigation will lead them to discover that these small white spots are not a sign of disease but are actually special spawning pimples that cover certain parts of male goldfish at spawning time. A tropical fishkeeper could become concerned that their Synodontis catfish are swimming upside down – this could be a sign of a swim bladder disorder. Again further investigation will lead the fishkeeper to discover that the fish are actually ‘upside-down catfish’, which swim happily in an inverted position when juvenile, often resorting to a more conventional posture as adult fish. These two examples highlight the need to know your fish! Know your fish starts before you have even purchased them from your aquatic store. When you read up on the potential size, feeding and water quality requirements of any potential new fish, try to also seek information about the natural appearance of the fish at different stages of their life cycle and their natural ‘normal’ behaviour. Kribensis cichlids (Pelvicachromis pulcher) for example show a markedly red belly at spawning time, this could be mistaken for bacterial erythrema. Clown loaches (Chromobotia macracanthus), are notorious for the eccentric behaviours. Youtube has a wealth of videos of healthy aquarium and pond fish, so these days we can see not only normal appearance but normal behaviour too. Upon acquiring your fish, you should familiarise yourself with the individuals natural appearance and its behaviour. In the first few days in the tank, your new fish are likely to be very timid and may decline feeding, however as they settle most common freshwater aquarium inhabitants will venture out into the tank and respond to feeding. Notice the swimming patterns of your fish, how quickly they eat food and the method of food intake. Feeding time offers an excellent time for a brief visual healthcheck of your fishes. However, as stressed above, we must be familiar with ‘normal’ appearance and behaviour of healthy fish in order to recognise ‘abnormal’ and thus potential ill health. Abnormal signs to look out for can be split into behavioural and morphological deviations from the accepted ‘normal’ state of your fish. Behavioural indicators of ill health include gasping for air at the water surface, a common sign of gill disease or water quality problems in most fishes – in air breathing fishes such as the Lungfish this is perfectly normal behaviour. Changes in the swimming activity are a sure sign of potential ill health. If a normally active fish ceases swimming activity, becoming lethargic and swimming only when disturbed, then this is a strong indicator of ill health. For sedentary carnivorous fishes, this is again a common ‘normal’ behaviour. Fish infected by skin parasites or irritated by certain water pollutants, will flick and scratch against objects in the aquarium or pond. Erratic darting motion instead of smooth swimming is often seen in small tropical aquarium fishes when they are infected by internal parasites or bacteria. These affect the swimbladder and occasionally the neuromuscular systems, which has an affect on posture and locomotory activity. Assuming an abnormal posture, such as a lopsided gait or even fully upside-down, is usually a sign of a swimbladder problem, a common complaint in fancy aquarium goldfish. The same problems can also cause the fish to lose its normal neutral buoyancy, and they either sink or rise when at rest. A fish that normally feeds voraciously, refusing food is a sure sign of ill health. As in all fish health problems, the first thing to check is that the water quality is within the preferred limits of the fish. As can be seen we must carefully observe our fishes when they are healthy in order to recognise behavioural changes shown when they are sick. The same is true for the external appearance of the fish, familiarise yourself with its colours, body contours and finnage. External signs of disease are all some deviation from the normal condition. If a fish’s skin is irritated either by pollutant in the water such as ammonia, or by infection with a skin parasite, the first response the fish will show, (In addition to the flicking and scratching mentioned above), is overproduction of mucous. The mucous layer is highly protective and the fish increases its production when the skin is irritated. This overproduction of skin mucous makes the fish’s colours look duller and it assumes a grey hazy appearance. Most external parasite infections cause generalised symptoms, one however, known as white spot, causes a very recognisable condition. As the name suggests, infection of the skin with the white spot parasite causes the fish to develop tiny white pimples over its body. The white spots are around 1mm in diameter, they tend to develop on the fins first before progressing over the body as the infection proceeds. Scaleless fishes such as Clown Loach are highly susceptible. Another very recognisable condition is finrot, although there are many possible causes. The fins of a healthy fish should be complete, symmetrical and of a uniform consistency. During finrot the skin between the bony fin rays rots away leaving the fish with decaying tissue where the fins used to be. If the cause of the finrot is identified and treated, the fins rapidly grow back. Finrot is caused either by water pollution, most commonly extremes of pH or ammonia poisoning. Infection with certain types of bacteria can also cause the problem. The delicate tissue of the mouth is also prone to a similar necrosis. Bacterial infection can also cause large open sores on the skin of the fish called ulcers. These are very damaging and must be treated early. Many internal problems can manifest themselves with external