Effects of two commercially available low-protein diets (21% and 31%) on water and sediment quality, and on the production of Litopenaeus vannamei inan outdoor tank system with limited water discharge

Effects of feeding Litopenaeus vannamei with commercial low-protein diets o n shrimp performance and on water and sediment quality were studied under h igh shrimp density with limited water discharge. Twelve tanks (each 10.5 m( 2)) were stocked with juvenile shrimp (average weight, 1.69 g) at a density of 40/m(2). Shrimp in six tanks were fed a 21% protein diet, and shrimp in the other six tanks were fed a 31% protein diet. Selected water quality pa rameters were monitored over a 94-day period. Shrimp growth, survival, feed conversion ratio (FCR) and selected sediment quality parameters were evalu ated at harvest. Shrimp survival was significantly higher (P = 0.041) in th e 31% treatment (96.2%) than in the 21% treatment (90.6%). Mean final weigh t of the shrimp in the 31% treatment (14.04 g) also was significantly highe r (P < 0.001) than in the 21% treatment (12.17 g). The FCR of the shrimp in the 31% treatment (1.75) was significantly lower (P>0.001) than in the 21% treatment (2.15). The gross production of the 31% treatment (540 g/m(2)) w as 22% higher than that of the 21% protein diet (441 g/m(2)). No significan t differences were found between the 21 and 31% treatments in the daily-mea sured water quality parameters (dissolved oxygen, temperature, pH, Secchi r eadings, and salinity) and the weekly-measured parameters (total ammonia-N, nitrite-N, nitrate-N, reactive and total phosphorus, 5-day carbonaceous bi ochemical oxygen demand (cBOD(5)), chemical oxygen demand (COD), total susp ended solids and volatile suspended solids (VSS)). Differences in sediment quality parameters (volume of sediment, COD, cBOD(5) and VSS) between treat ments were not statistically significant. This work shows that the 31% prot ein diet provided better production results than the 21% protein diet, yet it did not significantly deteriorate the water or sediment quality. (C) 200 1 Elsevier Science B.V. All rights reserved.