How much do our coarse fish eat?

FISH being cold-blooded, the amount of food they need to eat varies considerably throughout the year, with more energy required when the water is warm than when it’s cold.

On a typical summer’s day a carp will need to eat 0.1 per cent of its bodyweight. This means that a 10lb carp will need 2oz of food each day. That’s 50 boilies, 200 pellets, or a tenth of a tin of corn.

In winter, the amount the same carp needs to eat is massively reduced. Now, the same fish only needs 0.01 per cent of its weight each day. That’s five boilies, 20 pellets, or a pinch of corn. From these amounts you can see why you generally need much less bait in winter.

These figures are only a rough estimate and don’t take into account any natural food that the fish will eat, or that other factors such as dissolved oxygen can also have a big effect on how much fish will eat.

“Fats, which we often think are unhealthy in our diet, are much more important to fish”

What’s the food used for?

During the summer, any energy that a fish gains from digested food is split three ways. A big chunk is spent on just staying alive. Breathing, swimming around and feeding take up most of this energy.

Second, the fish will be growing in length, which not only means that the skeleton and organs need to grow, but the scales that cover the body also need to increase in size. It was once thought that fish grew right the way through their lives, but we now know, mostly from repeated captures of known fish over many years, that eventually fish will attain a peak size and stay around this length for many years. This is very obvious in carp, but has also been noted in chub, barbel, bream and pike, so is probably seen to some degree in most coarse fish.

Once the fish reach maturity, some of any energy left over will be used to produce eggs. The rest will become body fat.

This final part is important, because during the winter months it’s common among some species to not be able to consume enough energy to meet their daily demands, so they have to rely on their stored body fat reserves. For larger fish this isn’t normally a problem, because they have plenty of reserves, but especially in young fish less than a year old the amount of body fat can be very low in the smallest examples, and they can run out of their energy reserves and, in some cases, literally starve to death.

As the fat reserves are used up they are replaced by an increase in the amount of water stored in the body tissues, which explains why fish are often at their heaviest in spring, even though they have been using up their reserves.

Roach make a really good living out of leftover carp bait!

Which foods are ‘best’?

Just as with humans, there are good and bad foods for fish, although these differ quite significantly from what’s good for us. Fats, which we often think are unhealthy in our diet, are much more important to fish.

While humans and other mammals produce energy from carbohydrates (complex sugars), fish derive their energy directly from fat. Fish, then, don’t suffer from obesity in the same way as we do, but must have a relatively high level of body fat. The right level of fat in the diet also means that fish will use more of the protein they eat in building body tissue, so they grow faster.

A good diet for carp contains around 33 per cent protein, six per cent fat and three per cent fibre. Not surprisingly, this is what you will find in the carp pellets that many fisheries supply, and it’s also the basis for many boilies. Pellets with more protein or fat, such as halibut pellets, are simply more wasteful, as much of the excess goodness will pass straight through the fish and be excreted.

Bait such as sweetcorn contain much lower fat and protein levels than the optimal, but are useful in a mixed or balanced diet because they will counteract the impact of other baits that have higher levels of these nutrients. Baits such as luncheon meat tend to have much higher fat and protein levels, and so create more waste.

Of course, even when fish are fed a perfectly balanced diet the vast majority of the food will be wasted. Either it will not be eaten and break down on the lakebed, or it will pass straight through the gut of the fish and be excreted as waste. In heavily-stocked fisheries, trying to maintain a healthy balance of different foods (much of it bait) is important, but in this situation controlling the total amount of bait going into the water is more important to prevent it becoming polluting.

Some species of fish may make a great living out of waste carp bait. Anecdotal evidence points to roach, in particular, doing very well in heavily-stocked carp fisheries. It may well be that because they are omnivorous (reliant on a variety of food of both plant and animal origin), roach are able to make a good living by feeding on the scraps left over by the messy carp.