Techniques Used by Freshwater Fish to Evade Predators

When a predator launches its attack, it is time for prey fish to get out of the way — and quickly. Of course, anywhere will do to start off with, so long as it is away from sharp teeth, but if a chase ensues, how should a fish behave? Swimming along a predictable path could allow the predator to second guess its intention, but if it swims randomly, an individual could become isolated from its school, making it an easy target.

Where should fish head for if attacked?

Once a fish has decided to take evasive action, its next move will determine whether it lives or dies. For fish that live in the first few feet above the river or lake bed, the first move is almost always downwards, angling sharply towards the safety offered by rocks or plants. On the other hand, those that live at the top of the water column steer towards the surface, possibly taking advantage of any background of overhanging branches, etc., to break up their outline and make it difficult for the hunter to spot them.

Why do fish swim strangely when scared?

Fish under attack often adopt a swimming behavior known as "skittering." This refers to the way they dart about rapidly in an apparently haphazard fashion, turning sharply in different directions and making it hard for predators to catch them. As a general rule, predators are larger than their prey and, therefore, faster swimmers, so it would make little sense for an escaping prey fish to dash in a straight line — the predator would simply overtake and capture it. However, the size of the predator also makes it less maneuverable and it is this factor that the prey exploit with the sharp banks and turns seen during skittering. Even so, fish can only play this game for a short time — skittering quickly exhausts them — so to be safe, they must quickly find a hiding place.

Sometimes skittering succeeds in shaking off a predator, but with a really persistent predator the prey fish double back and fall in behind the predator, accepting this rather dubious and possibly shortlived haven.

Can any fish fly out of trouble?

Freshwater hatchetfish get their name from their extremely deep chests, which in conjunction with their slender caudal peduncle, makes them resemble a hatchet, or axe. This enlarged chest region holds the
massive muscles that power their sizeable pectoral fins. Why does the fish need such dramatic fins and musculature? The answer is equally dramatic: it is the only type of fish that is capable of true powered flight Unlike the flying fishes of the ocean, which simply jump and glide, hatchetfish are able to beat their winglike pectoral fins and propel themselves in a straight line for a few feet before returning to the water. They use this remarkable ability not only to catch flying insects but also to evade predators. One quick leap and they are able to distance themselves from their no doubt astonished hunter.

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