Water quality and partial mass budget in extensive shrimp ponds in Bangladesh

Abstract

In a Bangladeshi–Norwegian project, water quality analyses have been conducted in some brackish water shrimp ponds stocked with Penaeus monodon in Bangladesh. The water-sampling program included five extensively improved farms in the Khulna region and four improved extensive farms in the Cox's Bazar region, annually producing 100–500 kg ha −1. In addition to water sampling, data of input of manure, fertiliser and feed; shrimp stocking density, mortality and production; and water exchange rate data were collected. Measured pH, salinity and concentrations of dissolved oxygen and gaseous ammonia were usually within acceptable ranges for shrimp farming. However, sub-lethal levels of ammonia can be present and create stressing conditions. Low salinity could also create unfavourable environmental conditions. In one Gher, frequent sampling of inlet–outlet water was carried out during one production cycle. On average, the concentrations of total phosphorus and total nitrogen were reduced by 70% and 40% through the pond (inlet–outlet), respectively. Apparently, 80–90% of the supplied nutrients in fertiliser and inlet water was trapped in the pond. Consequently, the extensive shrimp culture in Bangladesh seems to act as a sink for solids and nutrients in the water that led to the system.