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Your guide to the behaviour of fish

Your guide to the behaviour of fish

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Fish are fascinating creatures, and if you’ve ever kept pet fish you’ll know they can show a range of behaviours, from hiding away to chasing each other around. But what do these different actions mean and should you be worried about any of them? To keep your fish happy and healthy, it’s worth understanding what’s normal and what might indicate a problem. Read on to find out some useful tips about fish cognition and behaviour.

Why do fish chase each other?

If you have a group of fish in your aquarium, you may notice some of them swimming after each other. This can be a normal behaviour, and isn’t always a cause for concern. However, if it becomes a persistent issue or is coupled with aggression, it can be a problem.

There are various reasons why fish may chase each other. If they are of different species, it may be that they just can’t get along because of their different natures. For example, goldfish and guppies will never be friends. This means it’s important to research the types of fish you’re intending to keep before setting up your aquarium or introducing new additions to the tank. Fish compatibility charts are handy resources that can help here.

If one or two of your fish persistently chase others of the same species, it may be they’re showing dominance behaviour. This is normal to some extent, but it can be a problem if it results in bullying and fighting. Sometimes having a larger group can help, as this makes the dominant fish less likely to pick on a particular individual. It also helps to check you have enough female fish around, as males can show aggression and rivalry when it comes to mating time if females are in short supply.

While adding more fish may help reduce chasing in some situations, this will only hold true if your aquarium is big enough. Otherwise, your fish may become too territorial in the limited space and this will worsen the problem. To avoid this, always make sure your aquarium is big enough and that it has enough open space as well as hiding places for more shy or submissive fish.

Different types of fish have different feeding habits and this affects how they behave.

Why do fish fight – and how do you stop it?

Fighting can crop up for similar reasons to chasing – incompatibility between species, dominance behaviour, or competition over space, mates or resources. Sometimes you will see your fish fighting, but other times the signs can be less obvious. If you notice split fins, wounds or missing scales, you can be suspicious that there’s some aggression going on.

To reduce fighting, make sure that you only introduce compatible fish and that your aquarium is not overstocked. Some fish such as cichlids are more naturally territorial and aggressive than others, and these will need enough space so that others do not keep encroaching on their territory.

If your fish are fighting, it can help to rearrange your scenery and decorations to provide separate territories with visual barriers between them, as well as creating lots of hiding places. However, if you’re unable to stop the fighting, you may need to separate your fish.

Fish feeding behaviour

Different types of fish have different feeding habits and this affects how they behave. Some fish are herbivores, which means they only eat plant matter, and these fish will need to graze frequently throughout the day. If you keep live plants in your aquarium, you’ll see the herbivores nibbling away at the vegetation.

Fish who eat meat will need meals less frequently, but they will often look ravenous when they do eat. This is because they don’t always have ready access to food in the wild, so they will gobble up food whenever they get the chance. Given that they always look hungry, it’s easy to overfeed fish – take a look at our article on how to feed fish to learn how to avoid this problem.

Why do fish hide away?

Hiding is natural for many species, and fish will generally tend to be shy when they are getting used to their new home. However, if your fish don’t seem to get braver as they settle in, or if they suddenly start hiding away more than usual, this may be a sign of problems.

Stress can cause fish to retreat into safe places, so an increase in hiding behaviour may follow a change to the environment or water conditions. If in any doubt, check the water parameters with a water test strip. Other perceived threats such as newcomers or bullies can also make fish hide away.

Another reason for hiding is that your fish may feel uncertain in their environment if there is a lot of open space. While it may seem counter-intuitive, adding more cover and hiding places to the tank may actually make your fish braver and more likely to swim about. For fish who naturally live in shoals, they will generally be happier swimming around if they have the protection of a large enough group.

Illness is a final concern, so if one of your fish has started retreating away more than normal, do check that it looks healthy and that it’s still eating well.

A big part of the behaviour of fish is communication with other fish.

What if fish are listless or swimming erratically?

If your fish seem to be tired or listless, this may indicate that something is wrong. Sometimes the temperature may be too warm or cold, so just check your thermometer and heater and make sure the water conditions suit your fish. Alternatively, your fish may be lethargic due to overfeeding, so it’s worth checking that there is no leftover food when you feed them.

Illness is another potential reason for fish swimming unusually, and if you notice that one of your fish has sunk to the bottom or floated to the top, or seems to be struggling to stay balanced, this may be a sign of swim bladder disease. Other strange behaviours like rubbing against surfaces can indicate other problems such as parasites.

When do fish sleep?

A common question about the behaviour of fish is how they sleep – or whether they do so at all! Fish don’t sleep in quite the same way we do, but they do go into a restful state that shares many of the features of our shut-eye. When in this state, the fish stay still, breathe slower and the rate of their metabolism decreases.

Most aquarium fish will sleep in the night, but some such as catfish can be nocturnal. Having a constant light/dark cycle for your aquarium is important to maintain the sleeping habits of your fish.

How do fish communicate?

A big part of the behaviour of fish is communication with other fish. There are lots of ways fish can send each other signals, and these include body language and motion. For fish that tend to swim in groups, this is an important part of communication and their synchronised swimming is impressive to behold!

Motion isn’t the only way fish communicate though – some are even capable of brightening or changing their colour to send particular messages. Smell is another part of the fish social scene, with various species using pheromones to talk to each other. What’s more, though we can’t hear it, some fish can use sound to communicate, producing the noise by vibrating their swim bladders. All in all, fish are very talkative for creatures who can’t talk!

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