Nitrogen assimilation potential of seaweed (Gracilaria verrucosa) in polyculture with Pacific white shrimp (Penaeus vannamei)

In order to evaluate the nutrient absorption efficiency of combined shrimp and seaweed production, nitrogen fluxes in polycultures were compared with shrimp monoculture systems. Therefore, triplicate concrete tanks, with a volume of 3 m3, were stocked with shrimp Penaeus vannamei (6-7 g, 5 ind/100 litres) and seaweed (Gracilaria verrucosa) in densities of 0, 3.125, 6.250, and 9.375 g L-1. The culture period lasted four weeks and water samples were taken every week to measure nutrient fluxes. The use of seaweed at a density of 3.125 g L-1 in shrimp polyculture showed the highest ability for nitrogen assimilation originating from shrimp waste. This treatment increased shrimp survival rate from 63% (without seaweed) to 83% and the growth performance of shrimp from 247.78 g (without seaweed) to 350.20 g. Remaining nitrogen excreted by shrimp amounted to 15.36 g, which was mainly (14.62 g) utilized by seaweed to form a biomass of 16.90 kg. Therefore, polyculture systems using seaweed seem to act more efficiently with regard to nutrient accumulation.