The fate of nitrogenous waste from shrimp feeding
This study characterized and quantified the dissolved nitrogen (N) waste from shrimp (Penaeus monodon) feeding. The subsequent utilization of the dissolved N (DN) compounds by the microbial community in shrimp pond water was also examined. There were three main sources of soluble N from feeding; gill excretion, leaching from formulated feed, and leaching from shrimp faeces. The main source of DN was ammonia excreted from shrimp gills. However, there was also a significant amount of DN leached from feed and faeces over the course of a few hours. Most of this was in the form of dissolved organic N (DON) compounds. In the case of feed, a significant proportion of this was dissolved primary amines (DPA, 23%) whilst in faeces, it was urea (26%). Urea leached from shrimp faeces was rapidly utilized by the microbial community in pond water. However, other DON compounds appeared to be less bioavailable. Dissolved organic N leached from formulated feed appeared to be less effectively utilized by the microbial community and is likely to accumulate in pond water. Dissolved organic N leachates from formulated feed and faeces are, therefore, likely to have a significant impact on water quality in shrimp ponds, both by the accumulation of DON, and stimulation of the growth of the microbial community. There is, therefore, considerable scope to improve water quality, and hence reduce nutrient discharges from shrimp farming, by reducing overfeeding, and improving feed retention by shrimp.