Understanding the Reproductive Biology of Fish

The reproductive biology of fish is fascinating. Mother Nature has arranged it so that the reproductive habits and nurturing instincts of each species are designed to maximize the species’ chances of survival.

In a big-fish-eat-small-fish world, it is best when both male and female parents are able to maximize their reproductive output, raise more young during their lifetimes, and nurture the broods during the most vulnerable stages of their lives.

How Many Fish Species Provide Parental Care?

Different species care for their young differently. About 20 per cent of fish species provide parental care. In about three-quarters of these, parental care is provided by only one parent. About one in 20 fish species provides bi-parental care for their young.

Are Fish Monogamists or Polygamists?

As far as the male is concerned, the numbers of young that are lost to predators or lack of nutrition can be more than made up for if he fathers another brood. True monogamy is rare, though not completely unheard of.

One known species of a “faithful” fish is the Midas Cichlid (Amphilophus citrinellus). The males probably don’t stray because the females will only mate with partners who demonstrate a high degree of fidelity and paternal care. No matter how many available females there are in the vicinity, it seems that males will not stray! Researchers have observed that if the males do stray, available females are likely to reject his advances. Thus, the best strategy for the male is to stick to one partner.

In contrast, some species practice polygamy to increase their survival rates, as a group of adults can defend their territory and broods better than just one partner, or even two.

Are the Roles of Parenthood Create Equal?

The contribution of males and females towards their parental duties are unequal. The males usually put a great deal of effort into staking out and acquiring a conducive territory for the eggs to be laid, and build the nest. The females visit the nests, choose their mates and lay the eggs. The males then fertilize the eggs.

It is more likely for males to be the main care providers. Their defensive instincts peak when the brood are at the egg and “wriggler” stages. However, males often become less protective and almost desert the brood before the females do, especially once the brood become free-swimming.

If there are large numbers of females, a male can potentially benefit by deserting his present brood. However, males are less likely to desert their broods if the existing threat posed by predators in their habitat is high.

Females, on the other hand, become highly aggressive towards any fish that approaches their brood, and this behavior persists for several weeks.

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