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 23ºC, 28ºC and 33ºC, and salinities of 10, 15, 20, 25, 30, 35 and 40‰. Oxygen consumption of Litopenaeus stylirostris exposed to experimental salinities increased in direct relationship with temperature, even though at 28ºC the metabolic rate was steady. The ammonium excretion rate in juvenile shrimp acclimated at 23ºC and 33ºC 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 28ºC. 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 33ºC 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 23ºC, 28ºC and 33ºC were 0.25, 0.17 and 0.3, respectively; the lowest value was obtained for juveniles maintained at 28ºC, 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 28ºC, considered the optimum conditions because in these environments the organisms are free of stress and their growth therefore increases.