Mortality of pacific white shrimp submitted to hypothermic and hyposalinic stress

Abstract

Abrupt changes in water quality parameters affect strongly the growth, survival and resistance to disease of farmed marine shrimps. However, unlike the determination of the toxic levels of substances affecting 50% of the population, standard protocols to nontoxic stressors tests are often neglected. The main objective of this work was to establish the lethal temperature (LT₅₀) and salinity (LS₅₀) for 50% of the population. Juvenile shrimps weighting from 10 g to 12 g and 17 day-postlarvae reared at 28 °C temperature and 32‰ salinity were submitted to hypothermic stress for one hour at temperatures of 7°C, 10°C, 11.5°C, 13°C and 16°C (juveniles), or for 72 hours at temperatures of 11°C, 12°C, 13°C and 14°C (postlarvae). Besides hypothermic stress, juveniles were submitted to 24 hours hyposaline stress in water having 0‰, 3‰, 6‰ and 9‰ salinities, and the postlarvae for 72 hours in water having 0‰, 1.5‰, 3‰, 4.5‰ and 6‰ salinities. Mortality rates were determined after those periods. The LT₅₀ were 11.7 °C for juveniles and 12.9°C for postlarvae, and the LS₅₀ were 2.4‰ and 1.8‰ for the juveniles and postlarvae, respectively.