METABOLITE PRODUCTION-RATES FROM ATLANTIC SALMON (SALMO-SALAR L) AND ARCTIC CHAR (SALVELINUS-ALPINUS L) REARED IN SINGLE PASS LAND-BASED BRACKISH WATER AND SEA-WATER SYSTEMS

Metabolite production rates of several groups of Atlantic salmon (60 g and 2000-4000 g) and of Arctic char (47-70 g) kept in seawater or brackish water in single pass, land-based rearing units, were examined. The metabolites measured were total nitrogen, ammonia, urea and total phosphorus. For fish fed on a continuous light and feeding regime, the daily variation in metabolite production rates was small. Typical daily variation patterns were found for the ammonia production rates, but not for urea, for fish fed between 08.00 and 20.00 hours. For these fish, the average ammonia production rate during the day seemed to occur between 15.00 and 16.00 hours. The average percentages of total nitrogen excreted as total ammonia were in the range 61-67%, while 7-10% were excreted as urea. The average production rates (mg Nitrogen/(kg fish min)) of total nitrogen, total ammonia and urea increased linearly with increasing specific growth rate under the experimental conditions used. The production rates of total ammonia, when expressed as g/kg food, decreased with increasing conversion factor. The structural relationship between ammonia production and conversion factor is also accounted for theoretically. © 1990.