Culture experiment on the growth and production of mud crabs, mullets, milkfish and prawns in Mtwapa mangrove system, Kenya.

Abstract

Experimental culture of crabs, fish and prawns was conducted in a pond measuring approximately 800 m2 in Kwetu training center, Mtwapa, Kenya. The objective was to evaluate the success, potential and economic viability of the culture system. Crabs were placed in 6 experimental cages measuring 2 x 2x 0.5m for 3 months in different stocking densities in order to compare their survival. The three densities were 3.0, 6.0 and 9.0 crabs/m2. Other crabs were placed in compartments made of locally available ‘fito’ designed in eight compartments measuring 1x1 x 0.9 ft for crab fattening. In the same pond, 2045 juvenile prawns Penaeus monodon and P. indicus measuring between 21-25 mm in total length were stocked inside the pond to grow, together with milkfish and mullets. At the end of 3 months, harvesting was done for crabs, and after 6 months for prawns and fish. Environmental variables were measured in the pond biweekly during the six month period. This included, temperature, salinity, chlorophyll a, nitrates, phosphates and pH. Higher survival of crabs occurred in the cages that had a stocking density of 3.0 crabs/m2. For crab fattening, highest mean growth per month was 24.6 gm, while lowest was 6.7 gm. A mortality of 43% was experienced during crab fattening at the end of the culture period. Recapture of prawns was poor due to inability to drain the pond completely, and mortality, however a number of fish by catch are reported. Constraints and recommendations are discussed.