NATURAL SPAWNING IN OPEN WATERS
This describes the means by which
fish breed in the wild to produce their seed (see section 6.1). Different fish
species usually choose different places in the aquatic environment for
breeding. The reasons for the choice are not always fully known and depend on
behaviour and adaptation of the fish species. For instance, some breed on
stones at the bottom of the water. Others make holes in the benthos for
breeding; others lay their eggs in holes, on the water while others collect and
brood the fertilized eggs in their mouths. In nature, the cues or signals that
induce spawning are numerous, e.g. flooding (increase in water volume), rain
events, changes water temperature, increase in food, etc.
As
the natural aquatic environment is full of hazards or perils for young fish,
fish have evolved varying degrees of parental care to help reduce the level of
mortality for the young. Some care for the eggs only, moving away some after
the eggs are hatched. For others, protection continues until the young are able
to fend for themselves. Cichlids, i.e.
some tilapias, have elaborate parental care, including carrying the young in
the mouth at any approach of danger. As a rule, species with elaborate parental
care lay relatively few eggs, while clupeids and catfishes (e.g. Chrysichths nigrodigitatus, Clarias
gariepinus, Heterobranchus bidorsalis) with little parental care produce by
far more numerous eggs, as a way of ensuring that some, at least, will survive
to adulthood. Fry, fingerlings and juveniles are collected from open waters by
artisanal fishermen using baskets, fine mesh nets and cane traps. Collection is
always easier during schooling (especially for Heterotic niloticus). Fish farmers purchase the northern and north
central zones of the country depend largely on wild fingerlings from the vast
inland water resources such as lakes and reservoirs. However, wild stocking of
fish farms has almost disappeared in the south.
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