FEEDING KOI AND GOLDFISH
Koi eat a lot, goldfish do too, but goldfish are better foragers. If you took two identical ponds and you neglected to feed both ponds equally, the population in the koi pond would die out faster than the population in the goldfish pond. Part of the reason is that koi eat more, so they starve faster. Part of the reason is that goldfish will find food anywhere, including swimming prey like rotifers, fish fry and insect larva. koi on the other hand tend not to identify or attack small prey like that. Their usual foraging method is bottom sifting. And if the pond has no aggregate or mud on the bottom, there will be no natural forage.
Feeding in cold water
Fish will feel 'hungry' in cold water, even down to the mid forties. However, the enzymes needed for the digestion of most koi food will be lacking. The fish will eat, sometimes fully, and then languish in the cold water as they slowly digest and metabolize the food. In very cold water, fish simply don't eat. If the food is going to be processed by "cold" fish with impaired metabolism, it has made sense to most people to offer foods which are easily and quickly digestible and which contain minimal residue to stall the gut. Over the years, soluble plant proteins like wheat germ were found to be effective, and so were Cheerios. Fish love Cheerios, especially Honey Nut Cheerios. Try it, you will see they go for the darker, tastier(?) Honey Nut Cheerios over the plain ones. And they can tell when you buy generic Cheerios. But it's okay.
The point of Cheerios is that they supply some useful energy, with minimal nitrogen to strain a cold biological filtration system, and the fish like 'em…a lot. In my own pond, I've noticed that Cheerios are sort of fattening when offered with regular food year round, so if you want to put some weight on a big female fish, especially through her face, give her some Cheerios with her regular diet through the year.
In cold water I recommend that you:
Refrigerate foods, DON'T freeze them. Freezing damages (lyophilizes = freezer burns) the fats in the food and so the fat-soluble vitamins are compromised.
So, we've talked about feeding, let's talk nutrition. What's in food and what does it do?
Studies have been done which compared the digestion and assimilation of protein in fish. They tested chicken protein, fish protein, plant protein, beef protein, pork, etc. And you will NOT be surprised to know that fish proteins were the BEST digested and assimilated. Fish eat fish. This makes sense because the incidence of fish leaping onto shore and eating cows is very, very low to non-existent. Fish are adapted to the consumption of others in their food chain. So fish proteins are the best for fish. Cool.
Fat is important in a diet to carry energy and at-soluble vitamins to the fish. Fat supplies a dense energy source. However, fat is a dangerous component in foods because when it gets too high, it can cause the food to spoil more easily, and can even stimulate the growth of certain moulds. So manufacturers are VERY careful about the fat content of foods. Fat content of 3-9% is safe and reasonable.
Carbohydrates are the immediate energy source for the fish. Due to their carnivorous nature, fish tend to be poor at utilizing carbohydrate (Trout are utterly diabetic) so they may store it in the muscle or discharge it in the waste. This doesn't change the fact that it's important. It's usually not listed as a percentage on most fish food labels. I am not attaching too much significance to it in this article. So when you look at a bag of food and the first ingredient is "Wheat". Again, you get the picture. Wheat is not equal to fish protein. So keep looking. You should look for fish or aquacultural proteins as the first ingredient in a decent diet for your koi and goldfish.
Much discussion exists about the mineral requirements of fish. I personally recommend that if a food for koi contains some extra calcium, and contains low phosphorus, it could be considered "better" than a food that pays no attention to the calcium and phosphorus.
©2014 Delaware Valley
Water Garden Society