Outswimming Predators on the Reef

Sometimes it can be easy to forget that, despite the ingenious defenses used by fish to keep one step ahead of their predators, the one thing that can mean the difference between life and death is a real turn of speed when attacked. Most tropical marine fishes live in close proximity to the reef and are able to dart very rapidly to the safety it provides.

What gives prey fish their speed?

Fishe's bodies are packages of extremely lean swimming muscle, accounting for up to 80% of the fish's overall weight. In simple terms, this muscle can be divided into two distinct types, distinguishable by their color White muscle is used to provide explosive power of the kind used by human sprinters and weightlifters. Red muscle is very well supplied by the blood, as its color suggests, and is rich in oxygen. It provides steady, long-term power and is used by the animal as it cruises along.

By contrast, white muscle is comparatively poorly supplied by the animal's circulating blood, hence its color. Although it provides a great deal of power over short distances, enabling the fish to accelerate to safety when danger threatens, white muscle fatigues quickly and few fish can maintain escape speeds for more than a minute. As a result fish seldom stray so far from their preferred hidey-holes that they cannot dash back when a predator appears. When reef fish are moved into a new habitat, such as an aquarium, they often respond by appearing extremely nervous for the first day or two. This is because they have yet to learn the layout of their local habitat. Gradually, as they are able to assess where refuge is to be found, they calm down noticeably.

How can fish maximize their chances of making it to safety?

Although reef systems can be huge, most fish remain within relatively small areas, either within their own territory or in a limited home range. In each case, fish are usually excellent at memorizing the location of all possible bolt-holes; if a predator attacks, it makes sense to know where to find safety in a hurry. The larger the fish, the more risks it can take. Larger fish have fewer predators and can swim faster than their smaller cousins. Planktivorous reef fishes gather into large aggregations during the day, but these groups are assorted by size: larger fishes are confident enough to stray further from the safety of the reef, while smaller individuals remain close to their shelters.

How can fish make sure that they spot a predator early?

Reef fish are highly attuned to the behavior of the other fish in their habitat. If one individual spots an approaching predator and darts for cover, the others will usually respond by following suit. In this way, the danger message is passed rapidly right across all the fish communities on the reef. Although each fish acts as an individual, it benefits from the many eyes that keep a lookout for approaching trouble.