Parental care can be defined as an association between the parents and the offsprings, so as to increase the chances of the survival of the young ones, and in fishes it includes all the post-spawning care of the offsprings by the parents. Most fishes do not care for their eggs or youngs and leave the spawning grounds soon after fertilisation.
The lack of parental behaviour is correlated with production of great numbers of eggs and sperms. But there are many fishes where definite parental care has been evolved. Various devices have been adopted to ensure proper development of the eggs into adults. One or both the sexes may participate in the process. These include selection of a suitable site, nest building and various other methods of protection of the larvae.
Species which do not exhibit any special device for safety of the ova, generally produce a very large number of eggs to increase the chances of survival of at least a few of them. Eggs of many species possess various mechanisms for attachment to stones, pebbles or aquatic vegetation, so that they are prevented from being washed away with the current of water.
Nest Building:
Some fishes prepare crude nests for egg laying. At first a suitable place for preparing the nest is selected and some species may defend the place till death. Males of many species like the Darters (Etheostoma), sunfishes and cichlids, prepare a shallow basin- like nest for laying eggs by females. The stones and pebbles are removed from such nest and male keeps close watch over the eggs till hatching.
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A few species, however, leave the nest unprotected. Many freshwater fishes prepare crude nest with aquatic vegetation where eggs are laid. Protopterus and Lepidosiren prepare deep hole into which the females lay eggs. Males protect the nest till development is complete. Amia calva (bowfin) prepare a crude circular nest among aquatic vegetation.
The fertilised ova are protected by male who keeps guard over the nest till the young ones are hatched. The young ones are allowed to leave the nest in a body under the protection of father. Both the male and female of some cat fishes of North America prepare a crude nest in the mud for egg-laying. The nest is sometimes provided with protective cover of logs, stones, etc.
Most interesting example is provided by the male stickleback Gasterosteus aculeatus, a small freshwater fish of North American lakes and ponds. The male fish actually builds a nest of dead aquatic weeds which are joined together by a sticky secretion produced from the kidneys.
When the nest assumes