Oxygen consumption, ammonium excretion and osmoregulatory capacity of Litopenaeus stylirostris (Stimpson) exposed to different combinations of temperature and salinity

Abstract

The physiological responses of the blue shrimp were determined by exposing the organisms to temperatures of 23°C, 28°C and 33°C, and salinities of 10, 15, 20, 25, 30, 35 and 40‰. Oxygen consurpption of Litopenaeus stylirostris exposed to experimental salinities increased in direct relationship with temperature, even though at 28°C the metabolic rate was steady. The ammonium excretion rate in juvenile shrimp acclimated at 23°C and 33°C was related to the pattern of osmoregulation, increasing when the shrimp were hyper-regulators and decreasing when they were hypo-regulators. The ammonium excretion rate remained constant in shrimp kept at 28°C. The osmoregulatory capacity of the juveniles indicated that they were hypo-regulators and hyper-regulators in salinities above and below the isosmotic point, this capacity decreasing in organisms kept at 33°C and exposed to higher salinities. The isosmotic point obtained ranged from 676.8 to 700.7 mmol kg-1 (23.7-24.6‰). The values of the slopes between the osmotic concentration of the external medium and the hemolymph of shrimp acclimated at 23°C, 28°C and 33°C were 0.25, 0.17 and 0.3, respectively; the lowest value was obtained for juveniles maintained at 28°C, being strong regulators in this condition. To optimize the culture of L. stylirostris under controlled conditions, we propose that it be cultivated in salinities of 25‰ and temperatures of 28°C, considered the optimum conditions because in these environments the organisms are free of stress and their growth therefore increases.