Effect of repeated partial cropping on population dynamics and yield of Oreochromis niloticus (L.) during polyculture with Heterobranchus longifilis (Val.)

Abstract

The effect of repeated cropping of half the number of young and large adults on productivity and dynamics of 
Oreochromis niloticus was investigated during polyculture with Heterobranchus longifilis. Mixed-sex, large-sized 
and young adult tilapia of 841±0.3 g and 841±0.23 g were cultured with 40 catfish fingerlings in triplicate 36 m2 
earthen ponds in 1 and 2 treatments respectively. At the 4th, 6th, 12th, 26th and 32nd week, cropping was done in 
treatment 2 and the weights of the crop were used to enrich supplementary feed, by displacing an equal weight of 
ingredients in treatment 1. Realized supplementary feed crude protein level was 12.9 and 18.3±5% in treatments 1 
and 2 respectively. Feeding was at 1% body weight thrice daily. Weight data were analyzed with ANOVA and t-test. 
Surplus production of O. niloticus from treatment 2, calculated as sum of periodic harvest + final harvest minus 
final harvest in treatment 1, was 249±25 g per week. Treatment 2 had significantly higher H. longifilis harvest mean 
weight and growth rate (percentage per day) (p<0.01), with densities (p<0.05). It also has higher numbers of 
zooplankton and phytoplankton species, cyanophyceae and diatoms, as well as O. niloticus size susceptible to 
catfish predation. Chlorophyceae dominated the phytoplankton in both treatments. The implication of tilapia 
surplus production for catfish-tilapia polyculture is thus discussed.