SALINITY TOLERANCE OF JUVENILE SCALLOPS (PECTEN-MAXIMUS L) AT LOW-TEMPERATURE

The effects of reduced salinity on survival, filtration rate and behav iour of juvenile scallops (Pecten maximus) were studied at 5.0-degrees -C and 9.4-degrees-C. Daily observations of mortality and behaviour, a nd weekly measurements of filtration were made for 30 days at the orig inal salinity of 33 ppt, and at reduced salinities (29, 26. 23, 20 ppt , and weekly fluctuating between 27 and 29 ppt) and thereafter for a 1 5-day recovery period at the original salinity. The results show that there was no mortality in scallops at 9-degrees-C at salinities above 20 ppt and only low mortality at 20 ppt, while the scallops at 5-degre es-C had high mortality (> 50%) at salinities lower than 26 ppt. The f iltration rate showed little variation between salinities above 20 ppt at 9-degrees-C, and between salinities at 5-degrees-C and 20 ppt at 9 -degrees-C. The filtration rate in salinities over 20 ppt at 9-degrees -C was 4-5 times higher than at 5-degrees-C. The scallops responded to reduced temperature and salinity by retracting tentacles and mantle e dge or closing valves. It is recommended that scallop farms in western Norway should be located in areas where salinity seldom drops below 2 9 ppt.