Theo take a look at this thread and add to it what is above. Then tell me what you are looking for. I may be able to find an answer or at least some more questions. This is not new to Fisheries Science as Swingle was doing research on tilapia in ponds in the 50's and the study above was in 1984.

http://www.pondboss.com/cgi-bin/ubbcgi/ultimatebb.cgi?ubb=get_topic;f=5;t=000459;p=1