Effects of complete and supplemental diets and organic pond fertilization on production of Macrobrachium rosenbergii and associated benthic macroinvertebrate populations

Abstract

Growth and population characteristics of freshwater prawns, Macrobrachium rosenbergii, fed either a complete diet, a supplemental diet (with fish meal replaced and vitamin and mineral supplements deleted), or the supplemental diet with an adjunct organic pond fertilization regime were examined. Effects of these treatments on potential forage organisms (benthic macroinvertebrates) were also evaluated. Juvenile prawns averaging 0.46 ± 0.49 g were stocked into nine 0.02 ha earthen ponds at 39 520 ha −1. Treatments were evaluated in triplicate ponds. There were significant differences ( P < 0.05) between the regression lines for sample weights over time (growth) in prawns fed the complete diet and supplemental diet without organic pond fertilization and between those fed the supplemental diet with and without fertilization. There was no significant difference ( P > 0.05) between regression lines for prawns fed the complete diet and those fed the supplemental diet with an organic pond fertilization regime. At harvest, yield, survival, individual weight, and feed conversion averaged 943 kg ha −1, 76%, 31 g, and 3.9, respectively over the three treatments. Deletion of vitamin and mineral supplements and replacement of fish meal in prawn diets was associated with a significant reduction ( P < 0.05) in total benthic macroinvertebrate populations, possibly due to increased predatory pressure by prawns. In ponds in which prawns were fed the supplemental diet, organic fertilization resulted in a significant increase ( P < 0.05) in total benthic macroinvertebrates and a 15% increase in average prawn weight at harvest. Results indicate that prawns may increase predation when essential nutrients are deleted from prepared diets and that the supply of potential forage organisms may be increased by organic fertilization.