The effect of temperature on juvenile Mozambique tilapia hybrids (Oreochromis mossambicus x O-urolepis homorum) exposed to full-strength and hypersaline seawater

The effects of temperature on the salinity tolerance of Mozambique-Wami tilapia hybrids (Oreochromis mossambicus x O. urolepis hornorum) were investigated by transferring 35 g/1, 25 degreesC-acclimated fish to 35, 43, 51 or 60 g/1 salinity at 15, 25 or 35 T for 24 h, and by assaying gill tissue for branchial Na+, K+-ATPase activity at the three temperatures after acclimating the fish to 15, 25 or 35 T for 2 weeks. Tilapia survived all salinities at 25 and 35 T; however, at 15 T, mortality was 85.7% and 100% in the 51 g/1 and 60 g/1 groups, respectively. There was a significant interaction between temperature and salinity, as plasma osmolality, [Na+] and [CI-] were significantly increased at 51 and 60 g/1 salinity in 35 T water (P<0.001). Additionally, muscle water content was significantly reduced at 43 g/1, 15 T relative to pre-transfer values (P<0.001). Branchial Na+, K+-ATPase activity was reduced at 15 T regardless of acclimation temperature, and 25 degreesC-acclimated gill tissue did not show an increase in activity when assayed at 35 T. Results indicate that the effects of a combined temperature-salinity transfer on plasma osmolality and ion concentrations, as well as muscle water content, are greater than when either challenge is given alone. Additionally, branchial Na+, K+-ATPase activity is altered when assayed at varying temperatures; in the case of 15 degreesC, regardless of acclimation temperature. Our enzyme activity data may indicate the presence of a high temperature isoform of branchial Na+, K+-ATPase enzyme. (C) 2004 Elsevier Inc. All rights reserved.