Abstract:
The experiments were carried out to evaluate the
effect of dietary protein level, the degree of incorporation
of a legume Vigna catiang (cowpea) in the diet and the ration
size on the reproduction of Oreochromis niloticus (L .).
Experiments on protein level were carried out at 20, 25, 30
and 35% dietary protein levels. Experiments on ration size
were carried out at 20, 30 and 35% protein levels in which
fish were given rations of 1%, 2% and 3% of body weight or
were fed to satiation. Eight substituted diets at two protein
levels (25% and 30%) in which the fishmeal component was
progressively substituted by the legume V_j_ catiang were
tested. All diets were isocaloric and fish were fed twice a
day. In all experiments a sex ratio of 2(J) : 1 ^ was used. Young
0. niloticus of initial mean weight of 10.6g ± 2 .5 were
studied for an eight-month period.
Daily food consumption was variable. The overall
mean food consumption decreased with increasing amounts of
the legume in the diets. But this was not significant. The
best growth performance was obtained at the 30% dietary
protein level for all rations and all protein levels. Growth
’decreased with increasing level of incorporation of the
legume, irrespective of the protein level, particularly in
males. The 30% fish meal (control) diet gave the best FCR and
PER for legume substituted diet experiments; these became
poorer with increasing levels of the legume in the diet.
Total number of spawnings decreased linearly with
increasing dietary protein level. In the substituted diet experiments, the number spawned and total number of spawnings
increased up to 18% and 42% legume incorporation at 25%
protein level and both increased with increasing substitution
level at 30% protein level. At all rations, the number of
spawnings tended to decrease with increasing protein level
but the number of spawnings were always higher when fish were
fed 1% or to satiation at any protein level.
The mean size at first spawning tended to
increase with dietary protein level and ration size, but the
minimum size was independent from both. Fecundity ranged from
11-322 and 52-237 for 25% and 30% protein levels respectively
and 14(2%, P2 0 ) to 563 (3%, P20 ) for all rations.
Fecundity was linearly correlated to the body weight while
relative fecundity was curvilinearly related to it.
Generally, larval size (dry weight) and condition
factor tended to increase with increasing legume substitution
in the broodstock diet at both (25% & 30%) protein levels.
There was no clear cut relationship between larval size and
broodstock ration size. There were no significant differences
in proximate composition of the larvae obtained from groups
fed substituted diets or fed different rations.
* With all diets, the growth was higher at 30%
protein (control) diet (P30 Vo ), but spawning was least in
fish fed on this diet. With all substituted diets 42-47%
incorporation of V\_ catiang into the diet seemed to be
favourable for the reproduction of 0_j_ niloticus irrespective
of the protein level.
