Understanding the role of feed in shrimp ponds and matching natural and supplemental feeds for sustainable shrimp production

The central hypothesis of this research is that the dietary requirements of shrimp are influenced by culture system and culture intensity. In outdoor ponds, nutrients in formulated feed can be eaten by the shrimp directly or indirectly, the latter by eating biota present in the water column or benthic community which incorporated waste nutrients. An integration of outdoor compartmentalized ponds and indoor tanks was designed to quantify the contribution of different routes (directly eaten, water column or bentic) to shrimp production in ponds. From the feed composition point of view it was assumed that DP:DE, fat:carbohydrate and NSP:starch ratio of a diet has major influences on the above mentioned feeding routes. A preliminary experiment was executed using two diets differing in DP:DE ratio and three feeding levels: 0, 45 and 90% of recommended intensive feeding level. The feeding routes were tested outdoor (ponds; 6 replicates) and indoor (tanks; 3 replicates) over a two months period, stocking 20 juvenile shrimp m-2. Shrimp growth was higher in the ponds while survival was higher in the tanks (P < 0.05). The DP:DE ratio of the diets did not affect growth and survival, except that calcium deposition was better with the high DP:DE ratio diet. In ponds, shrimp growth and survival was similar for the 45% and 90% feeding levels, and were better than with the 0% feeding level in terms of individual growth 47%, survival 47% and biomass growth m-2 350%. Among the 45% and 90% feeding level survival, individual growth and biomass growth m-2 was better in 45% feeding in both ponds and tanks. Concentrations of chlorophyll a, phytoplankton, zooplankton, benthos and total bacterial count in both water column and sediment declined gradually between the start and end of the experiment. The unexpected low response to changes in the DP:DE ratio might have been caused by a reduction in salinity due to heavy rain from 5 ppt at the start to 1 ppt at the end of the experiment. Measurements of gut fullness showed the shrimp consumed feed and natural food. Availability of the latter through the water and benthic routes declined with increase in shrimp biomass in the system. In spite of high consumption, the energy intake might have been too low for osmoregulation at these low salinity rearing conditions, limiting feed utilization efficiency. P. monodon is known to perform best at salinities above 20 ppt. Additional information from a follow up experiment executed at a salinity > 20 ppt is needed to fully explain experimental results.