THE EFFECT OF CONSUMPTION OF WOODY DEBRIS ON MARINE CAGE-REARED SALMON

Consumption of woody debris was common in salmon farmed near a British Columbian pulp mill. This study of a proposed technology designed to reduce the passage of debris into rearing cages noted: Consumption of woody debris occurred in 32 % of fish in modified cages and in 21 % of fish in the regular cage. Wood chips and bark were the dominant components of the woody debris consumed. The proportion of chips to bark in fish from both the modified and regular cages was the same. The tree species composition of the consumed wood chips reflected the chip composition utilised at the pulp mill. Debris-consuming fish from modified cages, however, had a greater average mass and larger number of items in their stomachs than did fish from the regular cages. Significant histopathologic changes were noted in the stomachs of affected fish, and fish in the modified cages suffered a higher mortality rate.