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”

“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!

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.

How fish communicate

The fundamental ability to communicate is something we take for granted and is a skill that is common throughout higher animals. But what about fish? 

Are they able to pass on information, such as the location of food supplies, warnings of imminent danger and the desire to mate? With the transmission of such information being so important for survival, it is hard to imagine that they cannot react to one another in some form or other. 

Fish such as these barbel will react off other shoal members behaviour

Fish such as these barbel will react off other shoal members behaviour

Warning signs

Perhaps one of the most common forms of communication is body language and this is something that we see in many fish species.

If you have ever watched a shoal of roach or minnows moving almost as one as they turn in unison, then you will be well aware that fish do exhibit body language and react to each other. For this to occur, and for shoals to form at all, must mean that fish recognise other individuals of the same species. It is thought that this ‘imprinting’ takes place soon after hatching, with fish associating with those that hatch around them. 

Body language in shoaling fish can also indicate the presence of danger, such as the approach of a predator. With an arched body and fins held erect, fish can signal danger very effectively. It only takes one individual to alert a huge shoal of fish to a threat, because the signal quickly passes from fish to fish. 

This same form of body language could signal the presence of a rig or bait that some have been caught on before to others seeing it for the first time. It is unlikely that the naive fish know what is putting their shoal-mates on edge, but they are sure to react to it by being guarded.

Chub are a species known for being crafty and, in a bid to stop the fish relaying warning signals to any shoal mates in the vicinity, many specimen anglers go out of their way to retain any fish caught in a keepnet, or put them back well upstream of where they have just been caught (as most chub bolt upstream once returned).  

Chub are known to bolt once returned, often spooking other shoal members

Chub are known to bolt once returned, often spooking other shoal members

Show of strength

Most coarse fish do not have complex mating rituals or show off to their potential mates or ward off rivals. Other fish are much more showy. African cichlids use body language to perform complex mating rituals and to discourage competing males. The same fish also build large pits from which to display during their spawning courtship, the size of the excavation being linked to the size and fitness of the male. 

Many species of animal, including fish, use displays to signal their strength to rivals. Even bream are thought to hold a territory and defend it from other males, primarily with a show of strength. 

These non-conflict behaviours make a lot of sense, especially among species which have more serious armaments. Large sharks, for example, may swim parallel to other individuals in a show of strength that keeps them at a distance from their competitors’ razor-sharp teeth. They roll their eyes and arch their bodies to indicate their size and willingness to attack. 

Pike can be very territorial and use signals to ward off rivals

Pike can be very territorial and use signals to ward off rivals

Sound and vision

Some fish species are able to communicate by sending out sound waves. Fish have quite complex hearing organs buried in their heads that can pick up sound waves, in the form of vibrations, travelling through the water. Cod are able to communicate with their shoal-mates by producing a sound through their swim bladders. This low-pitched drumming can travel several hundred metres, alerting other fish of their presence. 

Other fish species may make sounds as they crunch up tough foods, such as mollusc shells. This could alert and attract other individuals to potentially rich feeding grounds.  

Rolling and especially jumping, often seen in carp and several other coarse species, could also be partially a response to finding good feeding areas and wanting to signal this discovery to other fish. The sound will certainly travel a good distance in water, much further than in air, so this remains one of several possible reasons for this behaviour. 

Pheromones, chemicals produced by animals and plants specifically for the purpose of communication, are widely known and for many years were investigated in fish. While there still remains some evidence that fish can respond to certain chemicals in the water, especially around spawning time, much of the evidence suggesting that fish release pheromones when attacked or damaged by predators has now been debunked. 

Although they don’t have the same communication strategies seen in other types of fish, exactly how coarse fish signal to each other remains a fascinating subject. 

Rolling carp could be indicating to other fish that a good feeding area has been located

Rolling carp could be indicating to other fish that a good feeding area has been located