Physiological, biochemical and morphological indicators of osmoregulatory stress in 'California' Mozambique tilapia (Oreochromis mossambicus x O. urolepis hornorum) exposed to hypersaline water.
The salinity tolerance of the 'California' Mozambique tilapia (Oreochromis mossambicus x O. urolepis hornorum), a current inhabitant of the hypersaline Salton Sea in California, USA, was investigated to identify osmoregulatory stress indicators for possible use in developing a model of salinity tolerance. Seawater-acclimated (35 g l(-1)) tilapia hybrids were exposed to salinities from 35-95 g l(-1), using gradual and direct transfer protocols, and physiological (plasma osmolality, [Na+], [Cl-], oxygen consumption, drinking rate, hematocrit, mean cell hemoglobin concentration, and muscle water content), biochemical (Na+, K(+)-ATPase) and morphological (number of mature, accessory, immature and apoptotic chloride cells) indicators of osmoregulatory stress were measured. Tilapia tolerated salinities ranging from 35 g l(-1) to 65 g l(-1) with little or no change in osmoregulatory status; however, in fish exposed to 75-95 g l(-1) salinity, plasma osmolality, [Na+], [Cl-], Na+, K(+)-ATPase, and the number of apoptotic chloride cells, all showed increases. The increase in apoptotic chloride cells at salinities greater than 55 g l(-1), prior to changes in physiological and biochemical parameters, indicates that it may be the most sensitive indicator of osmoregulatory stress. Oxygen consumption decreased with salinity, indicating a reduction in activity level at high salinity. Finally, 'California' Mozambique tilapia have a salinity tolerance similar to that of pure Mozambique tilapia; however, cellular necrosis at 95 g l(-1) indicates they may be unable to withstand extreme salinities for extended periods of time.
Sardella
Brian A
BA
Department of Zoology, University of British Columbia, 6270 University Boulevard, Vancouver, BC V6T 1Z4 Canada. sardella@zoology.ubc.ca
Matey
Victoria
V
Cooper
Jill
J
Gonzalez
Richard J
RJ
Brauner
Colin J
CJ
D000704:Analysis of Variance; D000818:Animals; D017209:Apoptosis / Q000502:physiology; D001834:Body Water; D004326:Drinking / Q000502:physiology; D005880:Gills / Q000166:cytology* / Q000648:ultrastructure; D006400:Hematocrit; D006454:Hemoglobins / Q000378:metabolism; D006824:Hybridization, Genetic; D008855:Microscopy, Electron, Scanning; D008954:Models, Biological; D010101:Oxygen Consumption; D012623:Seawater; D012965:Sodium Chloride / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D013312:Stress, Physiological / Q000503:physiopathology*; D017210:Tilapia / Q000502:physiology*; D014882:Water-Electrolyte Balance / Q000502:physiology*
D006454:Hemoglobins; D012965:Sodium Chloride; D000254:Sodium-Potassium-Exchanging ATPase