Loss of appetite amongst fish
Author: Ben Helm
Pond problem solver: My pond fish appear to have lost their appetite
Koi Pond keeping can put many unnatural pressures on pondfish that these artificially selected fish have not had to contend with in their wild ancestral form. Over thousands of years, their physiology has adapted to a sedentary, slow moving existence in the mid to deeper waters of naturally murky water. Yet in artificial garden koi ponds, the water is crystal clear and does not provide much natural cover. Fish are generally kept in relatively high stocking densities and are encouraged to feed at the water's surface when their mouths actually point downwards, perfectly adapted for scavenging off the bottom. Furthermore, their natural carp-like daily feeding routine is to feed on an 'as and when' basis, as solitary fish, sampling and ingesting any potential food item. Compare this to the feeding frenzy of a garden pond, where fish may be limited to 2-3 feeds a day and consequently have no option but to devour their food like predators rather than scavengers, competing against other koi for every last pellet. This feeding behaviour is now regarded as the norm in pond keeping, something that can be used as a useful barometer to indicate the health status of pondfish. Generally, healthy fish will eagerly feed, unhealthy fish will suffer from a loss of appetite.
Responsible koi pond keepers should respond to rejection at feeding time as an indication that there has been a deterioration in the fish's environment or health. If we were not to intervene, then such symptoms may be the fore-runner of greater fish health problems.
There are several reasons as to why Koi fish may not feed, and it is a matter of discounting potential likely causes through a process of elimination.
1. Sudden changes in temperature
Koi fish are cold-blooded and their metabolism and appetite is determined by water temperature. We quite naturally don't expect Koi to feed in winter because of the reduced water temperature and a sudden drop in temperature in summer (for which the British climate has a reputation)
will have the same effect on their appetite. If you have noticed a recent cold snap, then so will your fish. To verify that a cold snap is the cause of a loss of appetite, take notice of how they feed once summer returns (if it does!)
2. Stress caused by Predators
The unwanted attentions of a heron or cat can cause fish to stop feeding through stress, becoming less tame through a self-preservation mechanism in response to the threat of
predation. If this has been the cause of your fish not feeding, then it is likely to be accompanied by them also being more withdrawn and less willing to come to the surface. Keep an eye out for a heron at first light or at dusk and similarly for a cat to verify whether this is the cause.
3. Different Food
Changes in diet can be a real turn-off for some pondfish. If they have become used to a specific food, or have been fed a particular food on a long term basis, then they may not immediately adapt to a new diet. Differences in smell (which is very important to most pondfish) and palatability can influence their reaction to a new diet. The fact that pondfish respond differently to a new diet may not necessarily reflect its quality, but merely that it is different from what they have been accustomed to. Persevere with the change and as long as the new diet is palatable, the fish will adapt to it.
4. Water Quality
The single most influential factor on a fish's health is water quality. If there have been detrimental changes to any aspect of a pondfish's environment, then it is likely to affect its behaviour and appetite. Water parameters that should be tested for are rises in ammonia or nitrite or fluctuations in pH, deviating from the desirable pH range of 7 to 9. If it is possible to detect any such changes in water quality then this would suggest a likely cause to their loss of appetite. If no changes have been identified, then water quality can most probably be discounted, but always keep an open mind.
5. Disease
It is quite possible for fish to be under attack from a pathogen without there being any visible signs of lesions or damage to fish tissue. Besides losing their appetite, fish suffering from a disease are likely to show 'classic'
behavioural changes associated with that disease. A very useful procedure is to take a mucus scrape and examine the sample under a microscope to view any likely parasites. If there are large numbers of parasites such as Trichodina, Gyrodactylus, Chilodinella etc visible then this is the likely cause of loss of appetite, and can be treated accordingly. This, however, is not completely satisfactory as it is better to identify the likely cause of the pondfish becoming more susceptible to disease in the first place, being able to prevent it from happening again having cured it.
Copyright Pets Parade Ltd. 2000
Other articles by Ben Helm
- Gasping Fish
- Pond Problem Solver: Holidays
- Preventing Heron Problems
- Steps to Growing Aquarium Plants
- Testing water, why and how?
- Why do I need an aquarium filter?
- Why do newly introduced fish die?
- Why is it oxygen important?