Adult Reef Fish: The Final Stage In a Fish's Lifecyle

The final stage in a fish's life cycle is adulthood. To reach this point, each individual fish must have overcome virtually insurmountable odds with a combination of good luck and good genes. They needed good luck in the earliest part of their existence as eggs and larvae, and good genes to provide them with the armory necessary to hunt effectively, avoid predators and win a place among the community of the reef. Finally, at this stage, the fish will get their chance to pass on those genes to their own offspring.

What changes accompany the transition from juvenile to adult?

The transition from juvenile to adult comes when the fish reach reproductive maturity. Their appearance changes, males and females become easier to tell apart and they often advertise their maturity through color patterns. Breeding adults are often far more colorful than juveniles, and adult males are sometimes more colorful than adult females.

But just as adulthood can change the way that fishes look it also changes how they behave. As juveniles, fishe's main concerns are to find food and avoid predators, but once they reach adulthood, reproduction goes straight to the top of their list. As a result, fish often become more aggressive as they seek to stake their claim, especially with members of their own gender. They may also start to defend territories and attempt to court potential mates.

Does reaching adulthood represent the last developmental stage?

Not always; many reef fishes, such as clownfishes, reach maturity as males and later change to being females (known as protandry). Others, such as many wrasse species, mature into females before developing into males (protogyny).

How long do reef fishes live?

The length of a fish's life is usually related to its maximum size. The smallest fishes often live fast and die young. The ever-present threat of predation means they cannot afford to hang around; they must mature early and breed rapidly. By contrast, larger fish, such as some groupers, may live for well over a decade. The fish with the shortest lifespan is the pygmy goby (Eviota sigillata), found on the Great Barrier Reef. It lives for no more than two months, only about three weeks of which is spent as a mature adult.

As fish approach maturity their growth slows, although it never actually quite stops. Fish show what is referred to as "indeterminate growth," so in fact the concept of a maximum size is slightly misleading. Although it can be difficult to determine the exact age of a fish from its size, older fish often have a typically hunched back, caused by their muscles tightening with age. However, few fish manage to achieve anything like old age in the wild, so although theoretically many species can live for several years, perhaps less than one in a million of those that start out as eggs actually does.

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