Effects of temperature and salinity on the oxygen consumption and survival of hatchery-reared juvenile topshell Trochus niloticus (Mollusca: Gastropoda)

Juvenile Trochus niloticus were successfully produced in closed recirculating hatchery tanks supplied with saline bore water. Juveniles (Js), after reaching 3 mm in shell diameter, undergo rapid growth where the relationships between the shell width (W) and total weight (Tw) and dry weight of soft body (Dw) are represented by the equations Tw = 0.305W(2.787) (r(2) = 0.995) and Dw = 0.0542W degrees(2.172) (r(2) = 0.976). During this period of active growth, the oxygen consumption rate (Ocr) can be presented by the equation Ocr = 1131.655/W-1.139 (r(2) = 0.933). The maximum oxygen consumption of 264 mu L O-2/h/gTw was recorded at 31 degrees C and 35 parts per thousand (parts per thousand); oxygen consumption is reduced and stress sets in when the temperature exceeds 34 degrees C. Js are less affected by salinity at low temperature than at higher temperature (24-TL50). At 31 degrees C, the salinity tolerance is between 23 and 51 parts per thousand. This is well within the operating temperature of a trochus hatchery situated in the tropics. For optimal growth it is recommended that a trochus hatchery in the tropics should maintain a water temperature of 30-31 degrees C and a salinity of 31-37 parts per thousand.