The evaluation of Macrobrachium rosenbergii and Tilapia aurea polyculture in Texas

Abstract

The feasibility of polyculturing Macrobrachium rosenbergii and Tilapia aurea was examined in 500 m('2) earthen ponds in central Texas. Monoculture of each species was also undertaken to provide comparative data. Secondary production and water quality were monitored to determine their influences on survival, growth and production of the culture species. Production of freshwater shrimp in 500 m('2) in central Texas was similar to that obtained in other temperate regions of the United States where similar stocking densities and initial sizes have been employed. At a density of 9 shrimp per m('2), average production was 1120 kg/ha. Polyculture increased production above that obtained from shrimp alone. At stocking rates of 9 shrimp and 1 fish per m('2), total production reached 2240 kg/ha. Combining fish with shrimp resulted in a recognizable but non-significant reduction in shrimp growth and survival. Competition for food appeared to be the primary interaction between the two species. The primary factors affecting shrimp growth were temperature, dissolved oxygen, stocking density and food availability. Growth rates were significantly reduced when water temperature dropped below 23C. A 54% decrease in growth rate was observed when dissolved oxygen fell below 5 mg/l. Increased stocking density had a positive effect on production and a negative effect on average size and size distribution. When food became limiting, the population mode shifted toward smaller size classes. The percentage of shrimp occurring in the largest size class was unchanged but the percentage of shrimp in the smallest size class was greatly increased. The overall result was a reduction in average size. Partial budget analysis indicated that net return from culture ponds stocked with shrimp at 8 per m('2) was higher than culture ponds with shrimp stocked at 2 or 4 per m('2). Partial budget analysis also indicated that shrimp-tilapia polyculture had a higher net return than shrimp monoculture ponds and that when supplemental rations were not added to shrimp monoculture ponds net returns were substantially reduced.