BROODSTOCK
CARE AND SELECTION OF BREEDERS
In
most cases broodstock selected from nature or bought at a fish farm are kept in
earthen ponds at a stocking density of 0.5-1/m2 and fed regularly
with agricultural waste products and sometimes with some trash fish. Egg
development will take place and about six weeks after a female has been
reproduced it can be used again.
In some area of Africa the water temperatures drops below 220c during the dry/winter season, which hampers egg development and artificial production.
This problem can be overcome by careful planning i.e. catfish can be reproduced artificially in the first month of the dry season and a double number of females can be injected in order to guarantee a sufficient number of eggs and by this catfish fingerlings could be produced 11 month per year. Another method to overcome this problem is to keep the broodstock permanently indoors in a hatchery. A complete breakdown of the natural annual reproductive cycle can be obtained after the broodstock is kept one year indoors and reproduction can be carried out throughout the year. The method is however not recommended by the here as it depends on the availability of high quality composed feed and often encounters diseases such as crack head and retarded growth in the breeders and an endemic disease in the produced larvae.
In some area of Africa the water temperatures drops below 220c during the dry/winter season, which hampers egg development and artificial production.
This problem can be overcome by careful planning i.e. catfish can be reproduced artificially in the first month of the dry season and a double number of females can be injected in order to guarantee a sufficient number of eggs and by this catfish fingerlings could be produced 11 month per year. Another method to overcome this problem is to keep the broodstock permanently indoors in a hatchery. A complete breakdown of the natural annual reproductive cycle can be obtained after the broodstock is kept one year indoors and reproduction can be carried out throughout the year. The method is however not recommended by the here as it depends on the availability of high quality composed feed and often encounters diseases such as crack head and retarded growth in the breeders and an endemic disease in the produced larvae.
Artificial
reproduction starts with the selection of females from broodstock ponds after
which they are transferred to the holding tank within a hatchery Ideally,
broodfish weigh from 2kg up with
larger fish being difficult to handle and often resulting in substantial egg
losses prior to stripping. In general mature females are selected according to
the following criteria;
* A well distended, swollen abdomen
from which ripe eggs can be obtained by slightly pressing the abdomen toward
the genital papilla. Ripe egg are generally uniform in size and an experienced
hatchery operator can see the nucleus as a small dark point in the centre of
the egg.
* A swollen, sometimes reddish or
rose colored genital papilla.
Note: From a practice point of view
it can be said that all females are “ripe” once some eggs can be pressed out
and if the eggs are more or less uniform in size (just put some of the eggs
onto the nail of your thumb and add a few drops of water and look). For male
broodstock there is only one criterion: they should be larger than 2KG and not
less than 7 month old.
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