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Fish eggs

Fish eggs The most common reproductive strategy for fish is known as oviparity, in which the female lays undeveloped eggs that are externally fertilized by a male. Typically large numbers of eggs are laid at one time and the eggs are then left to develop without parental care. When the larvae hatch from the egg, they usually carry the remains of the yolk in a yolk sac which continues to nourish the larvae for a several days as they learn how to swim. Once the yolk is consumed, there is a critical point after which they must learn how to hunt and feed or they will die.

A several fish, notably the rays and most sharks use ovoviviparity in which the eggs are fertilized and develop internally. But the larvae still grow inside the egg consuming the egg yolk and without any direct nourishment from the mother. The mother then gives birth to relatively mature young. In certain instances, the most physically-developed offspring will devour it is smaller siblings for further nutrition while still within the mother's body. This is known as intrauterine cannibalism.

Walsh told that removing the large fish in each generation caused declines in many traits spanning the life history, physiology and behavior of the fish. "We know that commercially exploited populations of fish usually are slow to recover when fishing pressure is reduced. Our research indicates that the over harvested fish stocks are slow to rebound because fishing selects for evolutionary changes in the life history of the fish. Because the changes in the fish are genetic, they do not immediately go away when fishing ceases," he added.

In certain rare scenarios, some fish such as the hammerhead shark and reef shark are viviparous, with the egg being fertilized and developed internally, but with the mother also providing direct nourishment.

the practice of harvesting the largest individuals from a fish population introduces genetic changes that harm the overall fish population, a Riverside graduate student and colleagues have determined. Removing the large fish over few generations of fish causes the remaining fish in the populations to become progressively smaller, have fewer and smaller eggs with lower survival and growth, and have lower foraging and feeding rates, the researchers report.

Focusing on the Atlantic silverside, a commercially exploited fish commonly found along the east coast of North America, the researchers conducted harvesting experiments under a variety of regimens. They reared the fish for five generations, selecting out the largest individuals from each generation. They then evaluated multiple traits, such as body size and the number of eggs, in fish from the fifth generation.