Prey Fish Avoid Predators By Hiding
Fish can also avoid the attentions of their predators by hiding whenever danger threatens. They can do this either by seeking cover in the substrate or among rocks; or fleeing to places where their hunters cannot follow. For example, fish may choose to tough it out in an inhospitable environment, such as in the shallows or in places where there are low levels of dissolved oxygen. All these "hideouts" are correctly referred to as "refuges" and are of over-riding importance in the survival of vulnerable fish. Anyone whose livebearers have given birth in an unplanted aquarium will recognize this.
How do fish decide when to hide and when to venture out?
Although the world is a dangerous place, especially for smaller fish, it is not an option to hide all the time; for one thing, hiding usually comes at the cost of missing out on feeding. So it pays to be selective and to respond only to immediate dangers; in the end, small fish may outgrow many of their predators if they can keep feeding and increasing in size. In the wild, fish often live side by side with their predators. Schools of smaller species, such as barbs and tetras, are even likely to be in constant visual contact with larger, piscivorous hunters. Research has shown that fish are able to assess the danger that a predator poses, not only by its size and appearance, but also by more subtle cues. These include watching its behavior to see whether it is actively hunting and assessing chemical cues. Remarkably, these can tell fish with a high degree of accuracy not only when a predator has fed but on what species. Prey fish show the greatest reactions to predators if they pick up the smell of their own species -- it tells them whether the hunter has a taste for them. When this happens, prey fish stop eating and become super-alert, and if the cues become strong enough, they may seek a refuge.
Who should hide?
The larger a fish grows, the safer it generally becomes. Small fish represent easy pickings for hunters, not only because they are easy to swallow, but also because they are slower swimmers and quicker to tire if chased. For this reason, small fish are less likely to stray far from safety, remaining near to dense weed beds and seldom venturing out into open waters. Newborn livebearers often seek cover among floating plants, as there are fewer predators towards the top of the water column. Clumps of Ricao or similar vegetation act
as a refuge and can be a lifesaver in a community tank
How do fish judge when it is safe to come out of hiding?
In a risky situation fish may seek refuge but they have another imperative: they have to eat as well as avoiding becoming food themselves. Sooner or later they have to come out. The unfortunate fact for small fish is that they have lower fat reserves than their larger brethren and cannot afford to shelter for as long. All in all, this means that the smallest fish have to be the boldest and the most adventurous, continuing to feed by necessity, even when threat levels send larger conspecifics into hiding.