The Influence of Stocking Density on the Swimming Behavior of Adult Atlantic Cod, Gadus morhua, in a Near Shore Net Pen

Cage design and stocking density are important aspects of aquaculture farm design, therefore understanding how fish behave at different stocking densities is critical information for farm managers. In this study, high resolution acoustic telemetry was used to investigate the swimming behavior of adult Atlantic cod, Gadus morhua, that were stocked at four densities (5, 10, 25, and 45 kg/m3). Acoustic tags were placed into the abdominal cavity of five fish per density treatment so their swimming behavior could be continuously monitored throughout the study. An array of hydrophones made it possible to calculate the position of each fish in three dimensions, at ∼2–5 sec intervals, for 4–30 d. Three underwater cameras were used to obtain additional data about the distribution of fish in the cage during the daytime. At the lowest density, the cod spent the majority (64.3 ± 0.08%) of their time in the bottom third of the net pen. As density increased, the fish moved higher in the water column, and this behavior was most evident at night, at all densities. At no time throughout the entire study were there any obvious occurrences of schooling behavior, even at the highest density (45 kg/m3)