Effect of pond aging on natural food availability and growth of the freshwater prawn Macrobrachium rosenbergii

Abstract

Most farmed prawns are cultured in earthen ponds in semi-intensive systems, with added feed. Newly dug ponds have low biomass and diversity of microbial and macroinvertebrate populations and therefore require adequate fertilization programs to improve the ponds’ natural productivity. Once established, ponds contain microbial and macroinvertebrate populations that are of high nutritional value to the prawns. The aim of this study was to examine the effect of pond aging on natural food production and its availability, and how it affects the growth performance of the prawn Macrobrachium rosenbergii. Experiments were conducted in 50-m 2 earthen ponds which were treated with hydrated lime, followed by organic and inorganic fertilization to obtain an adequate natural productivity level. Post-larvae were stocked in new ponds (pond age: 1–3 months) and in old ponds (pond age: 8–10 months) at a weight of 0.05 and 0.06 g, respectively, and stocking density of 80 and 72 animals/m 2, respectively. The prawns were cultured for 63 days, and were subjected to one of two treatments: offering artificial feed during the last 42 days of culture (treatment 1) or during the last 21 days of culture (treatment 2). In new ponds the juveniles grew in average 22 and 11 mg/day, respectively, for the 42 and 21 days of feeding treatments. In old ponds, utilizing the same conditions, the prawns grew significantly better ( P⩽0.05), averaging 48 and 21 mg/day, respectively, for the 42 and 21 days of feeding treatments. This is equivalent to prawn weight gain of 121 and 93% and biomass increase of 74 and 53% for the 42 and 21 days feeding treatments, respectively, in the older ponds over that of the new ponds. The improved growth in the old ponds correlated with an increase in the density and diversity of benthic macroinvertebrate, as evidenced by the increased numbers of zoobenthos in the old ponds and in greater diversity of food items found in the stomach contents of the prawns in the old ponds. The present work demonstrates a clear advantage of pond aging as applied to the culturing of M. rosenbergii in earthen ponds. Further work is needed in order to develop innovative techniques to shorten the pond aging process as it relates to the pond's microbial and macroinvertebrates populations.