Abstract:
The clariid catfish, Heterobanchus longifilis (l-IL) and Clarius gariepinus (CG) were the test animals used for the study of the effects of different temperatures on the rates of hatching, growth and survival of their fingerlings. The fishes were injected with fresh extracts of pituitary hormone from C. gariepinus to facilitate the maturation of the eggs which were fertilized immediately after stripping.
Parental crosses, hybrids and the reciprocals were heat-shocked (3so-40°C) and cold
shocked (O°C) separately. Similar crosses were also used as controls. That is, they were
treated to ambient temperature. The shockings were done about four minutes into the start
of fertilization and lasted about five minutes in each case. The timing was for the temperatures to have good effects before the developing zygotes could get to an advanced stage of cleavage. The hatchlings of both control and shocked crosses were reared to fingerling stage. The fingerlings were given compounded feed of three percent body weight starting from the fourth day of hatching. The tanks used for rearing were inoculated weekly with hay infusion for the supply of microorganisms.
The hatchability percentages were noted. Measurements on survival and growth rates were also carried out. Least significant difference (LSD) tests were carried out as appropriate on growth rates, survival ratios and hatchability percentages of various crosses under each treatment.
In the case of growth rate, the fingerlings of the heat-shocked crosses were found to
be comparatively viable with those of the cold-shocked crosses. They, however, have to be
rejected because of their very poor hatching and low survival percentages. The control and
cold shocks had equally significant (P<O.05) hatching percentage of S0%. The control
compared favourably with the cold in terms of survival but it has to be rejected too on the basis of inferior growth rate.
The fingerlings of all the four crosses that were cold-shocked performed best in
hatchability, growth and survival and hence superior to the fingerlings of the other crosses.
In this case, the cold treatment was analysed the best. For example, in the growth rate, it
performed highly significantly (P<O.Ol) better than the others. However, within the cold
shock,-there were four crosses just as in the others. A further analysis was therefore
necessary to be carried out since F-test showed all the four crosses to be highly significantly (P<O.O1) different from one another. The posteriori analysis eventually carried out showed the (]HL x <j> CG as the best selectable for-commercial or mass production followed by its reciprocal hybrid .
