IMPORTANCE OF REARING-UNIT DESIGN AND STOCKING DENSITY TO THE BEHAVIOR, GROWTH AND METABOLISM OF LAKE TROUT (SALVELINUS-NAMAYCUSH)

Juvenile lake trout (Salvelinus namaycush) were held at different stoc king densities (48 and 96 kg m(-3)) in rearing-units of different desi gn (rectangular plug-flow, circular and cylindrical cross-flow) and th e effects on behavior, growth and metabolism were examined. Ambient li ght levels and current velocities were measured in each of three tank sectors (upstream, middle and downstream) to determine their relative contributions to fish behavior and distribution. Rearing-unit design a ffected orientation to current, contact with surfaces, agonistic respo nses, turn rates and avoidance of or contact with other fish. Stocking density primarily affected contact with tank surfaces, avoidance and contact with other fish. Fish in circular tanks distributed themselves uniformly, whereas those in plug-flow tanks crowded upstream and thos e in cross-flow tanks congregated downstream. Stocking density affecte d fish distribution most in cross-flow and least in circular tanks. Am bient light, current velocity and total in situ aggression modified fi sh distribution at low stocking density, but at high density the effec ts of current velocity and total aggression were undetectable. Growth and food conversion were best in plug-flow, followed by cross-flow and then circular tanks. Net ammonia excretion and oxygen consumption wer e highest in circular tanks and lowest in cross-flow (NH3) or cross-fl ow and plug-flow (O-2) tanks. Ammonia production was correlated with s tocking density, but oxygen consumption was unrelated to density. Resu lts demonstrate the interrelatedness of abiotic and biotic factors in fish culture and the ability to control fish behavior, growth and meta bolism through the alteration of several physical and biological varia bles in the rearing unit. (C) 1998 Published by Elsevier Science B.V. All rights reserved.