Effects of pulp mill effluents and restricted diet on growth and physiology of rainbow trout (Oncorhynchus mykiss)

Juvenile female rainbow trout was exposed for 4.5 months (June to October) to two dilutions of untreated and activated sludge treated whole mill efflu ent from a pulp mill producing bleached ECF pulp. Two controls were used, o n fed ad libitum and a second receiving 0.5% feed of the body weight. All e ffluent exposed groups were fed an libitum. Mean weight of the fish was mea sured monthly. At the end of the experiment a number of physiological and b iochemical parameters were analyzed in order to establish the physiological status of the exposed fish in comparison with unexposed fish that obtained ad libitum or restricted amount of feed. The fish exposed to treated efflu ent grew significantly more than ad libitum control fish until August, wher eupon growth retarded in fish exposed to the lower effluent dilution (400 v /v), The growth of fish exposed to untreated effluent did not deviate signi ficantly from the control fed ad libitum. The results from the hematologica l analysis clearly showed that fish fed restricted amount of feed deviated significantly in most parameters compared with the control fed ad libitum. Fish exposed to treated effluent showed a response pattern similar to that of the control fed restricted amount of feed, whereas the fish exposed to u ntreated effluent showed a response pattern that did not deviate from that of the ad libitum control. The metabolic parameters suggested that fish exp osed to treated effluent had a higher metabolic demand than ad libitum cont rol and that the energy allocation at the end of the experiment was directe d to processes other than growth. The responses on hematology were mainly a consequence of the increased energy demand and were not primary effects. T he implications of using feed related parameters at field studies are discu ssed. (C) 2001 Academic Press.