DISCUSSION
The results of the study shows that growth
rates, feed conversion rate and survivorship were
favorable in fish fed with Multi feed and NIOMR fed fish
containing 300 fish/tank and 450 fish/tank as compared to
tanks feed with NIOMR feed and Multi feed at 600
fish/tank.
Size distribution analysis in terms of (bi-weekly
weight gain) indicates that at the lower stocking densities
of 300 fish/tank and 450 fish/tank, there was a higher
weight gain. At the higher stocking densities of 600
fish/tank, the size was smaller, with many smaller fish
being harvested. This observation could be as a result of
the argument made by [14] in a study conducted on the
effects of stocking density on growth, yield and
profitability of farming Nile tilapia O. niloticus fed Azolla
diet in earthen pond. His argument was based on th
stocking density cited as inhibitory factor for fish growth.
[15, 16] argued that competition for food could also be a
possible factor. Space limitation [15-17] and low dissolved
oxygen were highlighted as other factors. [18, 19] argued
that tilapia is a territorial and aggressive fish so that the
density effect on growth might be explainable by their
competition for territories, as well as the permanent stress
caused by crowding.
Survival rates were not affected by stocking density
which is consistent with [20] who reported that mortality
in Nile tilapia raised in cages was not dependent on
stocking density, though in this study there was high
mortality at week 10 in the fish fed with NIOMR feed in
450 fish/tank. This was due to poor water quality as a
result of pollution with excess feed. Other reports on
catfish support these findings [21, 22]. However, it must
also be well noted that the effects of density on survival
rate could be entirely dependent on the range of stock
densities. T ilapia cultures are fraught with the
problems of prolific breeding, overpopulation and
stunting. O. niloticus sexually matures at about 20 g
weights [23], but throughout the culture period of 24
weeks there were no record of spawning in any of the
tanks since there was no fry or small fish observed. This
could be attributed to the constant flow rate of the water
and the high stocking density of the fish in this study
unlike the earthen pond culture. This is in agreement with
[24] who reported that intensive tank culture offers
several advantages over the use of ponds in the sense
that the high density of fish in tanks disrupts breeding
behavior and allows male and female tilapia to be grown
together to marketable size. This result is encouraging for
the future of this system since there are concerns about
tilapia that have been genetically modified using
hormones [25].