Oxygen Consumption of Tilapia nilotica in Relation to Swimming Speed and Salinity

Abstract

Oxygen consumption of Tilapia nilotica (L.) at 25 C was measured for various swimming speeds at salinities of 0, 7.5, 11.6, 22.5, and 30‰.Oxygen consumption for a given swimming speed and salinity increased linearly with weight when expressed on a double logarithmic grid. Slopes of regression lines relating oxygen consumption and weight were less than unity, ranging from 0.5117 to 0.9887.Generally, oxygen consumption at 0, 7.5, and 22.5‰ was approximately equal; values at 11.6‰ were lowest and those at 30‰ highest. Presumably, energy required for osmoregulation was least in the absence of an osmotic gradient (11.6‰) and greatest when the osmotic gradient was highest (30‰). Assuming energy required for osmoregulation was zero at the isosmotic salinity (11.6‰), it was estimated that approximately 29% of the total oxygen consumption was required for osmoregulation at 30‰ and 19% at 0, 7.5, and 22.5‰.Plasma osmotic concentration was used as an index of capacity for osmotic regulation. Concentrations for unexercised fish remained about the same at 0, 15, and 30‰. At no salinity were plasma osmotic concentrations for exercised and unexercised fish statistically different at P < 0.05. However, there was a trend for concentrations for exercised fish to decrease from the unexercised level at 0‰ and to increase from the unexercised level at 30‰. Only at 15‰ were concentrations similar for exercised and unexercised fish. Of the salinities tested, fish were able to osmoregulate most efficiently at 15‰, the salinity closest to the isosmotic salinity.