It’s not just reptiles and amphibians that benefit from having their diets adjusted throughout the year. We know that in the wild, most species will adapt their diets to capitalise on an abundance of a particular food. Here’s how to implement the same nutritional fluctuations with aquarium and pond fishes…
Feeding Pond Fish in Winter
The nutritional requirements of koi vary considerably throughout the year, hence the need for different diets. For example, protein is necessary for growth, but can only be used at warm water temperatures (over 15°C). Therefore, in summer, we feed a high-protein food because the koi can use the protein to grow. Whereas, in winter, a lower protein food is sufficient because the koi are less active and not increasing in size.
Feeding protein-rich foods at low temperatures can even harm koi. Below approximately 10°C, few if any of the proteins will be used for growth. Some may be used inefficiently to produce energy for movement etc, but the majority will pass straight through the fish. The resultant protein-rich waste can have adverse effects on the water quality as it decomposes.
In addition, the digestion of proteins into amino acids starts at the front of the intestine where the enzyme Pepsin gets to work. Pepsin works best in acidic conditions where the pH is 1.5 to 2. If a koi consumes a diet rich in protein and then the water temperature drops, the acidic stomach conditions, together with raised levels of Pepsin, can remain in the early intestine for a prolonged period. This can expose the koi to the risk of stomach ulceration and future infection.
To avoid these two problems, many koi keepers simply stop feeding their fish when the water temperature falls below 10°C. The theory is that the fish can obtain what little nutrition they require from within the pond and from their stored food reserves. Whilst this may be a possibility in a natural, planted pond, there is unlikely to be sufficient food in a koi pond. The fish would therefore have to rely on stored reserves in the form of fat and muscle tissue. Not feeding over a 3 – 4 month winter period would lead to the koi being thinner and weaker in the spring, and consequently more susceptible to disease attack later in the year.
Do Fish Feed at Low Temperatures?
The behaviour of koi is greatly affected by the temperature of the water they are swimming in. The colder the water, the less active they are and the less inclined they will be to feed. However, they can acclimate to low temperatures. Even at temperatures of 5 – 6°C, koi can be seen to rise to the water surface to feed. However, their activities are greatly influenced by changes in the water temperature. If the water temperature quickly falls from 12°C to 10°C, the koi will stop feeding for a while whilst their bodies get used to the lower temperature. By contrast, if the water temperature rises from 5°C to 7°C the koi may feed quite actively.
In the winter, and particularly in shallower ponds, the temperature changes described can occur every day, with an increase during the day and a fall at night. It makes sense, therefore, not to feed your koi and other pond fish too late in the day as it is likely that the water temperature will start to fall before the fish have had a chance to digest the food.
Good quality wheat germ foods are formed largely from plant ingredients and are characterised by a higher roughage content. The digestible component of the food is quickly absorbed by the fish, but importantly, the remaining ingredients pass more quickly through the intestine. The higher plant content will also reduce the amount of Pepsin produced in the front of the intestine and result in less acidic conditions.
Feeding such a diet to your koi throughout the winter will support the condition of the fish, but will have no impact on their growth. The carbohydrates contained within the food are an important energy source for the fish and prevent them from having to use their reserves. As for the wheat germ – it will allow better utilization of the other ingredients in the food as well as being a valuable food source in itself.
Benefits of Feeding Fish in Winter
Providing koi and other pond fish with suitable food during the winter will have a beneficial effect on the health of the fish in the spring. If the fish have not had to use up their stored food reserves, they will be in better physical condition. However, there is also evidence that the amino acids in wheat germ can strengthen the immune system of the fish and ensure they can counter disease organisms which can cause problems as the water temperatures rise in spring.
In extreme cases, not feeding koi carp through a long winter can lead to vitamin and mineral deficiencies. This can manifest itself in many ways, including lethargy, lack of condition, susceptibility to disease etc. Providing suitable food in small quantities can help combat these issues.
The important aspect of winter feeding is that you should feed very sparingly. As much as the fish will eat in 2 – 3 minutes is sufficient. The keeper must remember that they are not feeding to encourage growth or enhance colouration, but simply to maintain the health of the koi.
Feeding Fish in Spring
During the spring, the days will begin to lengthen and the water temperature in your pond will start to rise. At water temperatures above 8°C your fish will become noticeably more active and will begin searching for food. Initially, just feed them once a day on a few floating food sticks or flakes. Don’t be tempted to feed too much too quickly. The first warm days are usually followed by cold conditions.
In late spring they will be feeding ravenously to build up their strength after the rigours of winter and to develop reproductive tissues. At this time, they can be fed 1 – 2 times a day, but only on as much food as they will consume in about 5 minutes.
The pump and filter should be restarted 1 – 2 weeks before you start regularly feeding your fish. Gradually increase the amount of food that you give to ensure that the filter bacteria can increase sufficiently to cope with the resultant increases in waste. As temperatures increase, the pump can be positioned in the deepest part of the pond. Pumps that have been running throughout the winter can be turned up and lowered to the pond bottom.
Waterfalls and fountains can be switched back on in mid to late spring when water temperatures are consistently above 8°C.
Koi Fish Diseases
When the pond fish awaken from their ‘semi-hibernation’ they will be very weak and susceptible to infection by parasites. Watch out for signs of fungus, gasping, scratching against underwater objects or a grey slimy coating to the skin. You may also notice one or more fish being very lethargic, keeping away from the other fish and remaining still on the pond bottom or near the water surface – sometimes close to the filter or waterfall inflow.
Treating the pond with a general external parasite remedy is advisable, although the worst affected individuals should be removed to a separate treatment container. Some pond keepers add a preventative treatment to their ponds in April to kill any parasites before they adversely affect their fish.
The spring is an ideal time to introduce new plants into your pond. The safest and most convenient way to plant your pond is by using the plastic baskets available from most stores. These come in a range of convenient sizes and permit the easy re-arrangement of the plants at a later date. The baskets are best filled with good quality nutrient poor soil or a special pond planting media. Large gravel should be added to the top of the basket to prevent the fish from disturbing the soil and clouding the water.