Effects of temperature and salinity fluctuation on the ammonium excretion and osmoregulation of juveniles of Penaeus vannamei, Boone

This study assesses the effect of temperature and fluctuations in salinity on the nitrogen excretion and osmoregulation of Penaeus vannamei juveniles to determine the lowest stress combination so that these can be used to opt imize production of the Mexican strain in culture. The ammonium excretion r ate of juveniles acclimated to 20, 24, 28 and 32 degreesC was measured. Flu ctuating salinity levels were applied to these animals in a sequence of 40 parts per thousand, 33, 25, 18, 11, 18, 25, 33 and back to 40 parts per tho usand. The results indicate that when the salinity was reduced from 40 to 1 1 parts per thousand the ammonium excretion of the shrimp was reduced. The osmotic concentration of the animals was hyposmotic as the salinity decreas ed from 40 to 25 parts per thousand, hyperosmotic during the 18-11-18 in V. interval and hyposmotic as the salinity increased from 25 to 40 parts per thousand again. The range of isomotic points over this range of salinity wa s 712-777 mmol Kg(-1). The ammonium excretion of P. vannamei exposed to the se experimental conditions can be attributed to the process of osmoregulati on because excretion was increased when the shrimp were hyper-regulating an d reduced when they were hypo-regulating. Based on our results, the animals experience the lowest stress in a temperature between 27 to 30 degreesC an d a salinity close to the isosmotic, point between 25-27 parts per thousand . We propose that this should prove to be the optimal temperature and salin ity regime for culturing the Mexican strain of P. vannamei.