culture research. I want to specifically thank my Brazilian colleagues in fish
culture, Amaury B. da Silva, Antonio Carneiro-Sobrinho, Fernando R. de
Melo, F. Ari Pinheiro, and J. Anderson Femandes for their collaboration and
friendship. Without the efforts of the biologists mentioned above much of
the research reported in this paper could not have been accomplished.
Questions pertaining to unpublished data should be directed to one of the
above biologists at the following address: Centro de Pesquisas Ictiologicas,
Av. Bezerra de Menezes, 2045, Fortaleza, Ceara, Brazil, 60.000.DiscussionBOWEN: Can you tell us if you have any idea of the fate of the agricultural products
or by-products which you used as feed? Did the fish consume these readily?
LOVSHIN: There is no doubt about it. They consumed them immediately. You could
see the feeding activity and when you examined the guts they would be crammed with
the materials. Now, as far as digestibility is concerned, that is another matter. They can
probably digest some of themat least a certain percentage of the available nutrients-but
a lot of their growth comes from the incorporation of nutrients into bacterial detrital
feeds. We found that to really get the best growth in the pond culture of tilapia hybrids,
we had to reach a certain level of pond fertility.
BOWEN: Is there any correlation between that level of fertility and feeding habits? DO
the feeding habits change at that level of fertility?
LOVSHIN: That is a good question. I don't know. All I can say is that we always used
extra supplemental food until pond fertility reached a certain point, and lowered the
feeding rate thereafter because we knew that the fish were getting a lot of natural feed
from the pond.
BOWEN: Secondary plant substances have been mentioned as obstacles to the utilization
of some agricultural by-products. Did you ever note anything that could be suspected as a
toxic effect from any of these substances which you used?
LOVSHIN: No. We used a castor bean meal which can be toxic, but ours had been
detoxified by roasting. It was a good product for us because the animal husbandry people,
pig and cattle raisers, do not like to use castor bean meal because it gives their animals
intestinal problems. It does not kill them, but it irritates the intestines and causes diarrhea.
We could get this particular material very cheaply. In my paper, there is a comparison
between castor bean meal, cottonseed cake and palm nut cake, and the castor bean meal
is by far and away the best because it has the highest protein level. We used the whole,
ground castor bean seed which has an outer shell which is very hard and indigestible. In
an aquarium, the bottom would be literally covered with these hulls, but we never had
any toxicity problems.