Growth depensation and group behaviour in juvenile hybrid striped bass Morone chrysops×Morone saxatilis: effects of group membership, feeding method, ration size and size disparity

The effects of group membership (three group sizes), feeding method (single site v. scattered), variation in ration size (low v. high) and starting size disparity (range of starting sizes) on growth, growth depensation and group behaviour of juvenile hybrid striped bass (HSB) Morone chrysops female × Morone saxatilis male were tested. Group membership, starting size disparity and ration size affected the growth, growth depensation and behaviour of juvenile HSB. Growth was higher in fish held within large group memberships and high ration treatments. Growth depensation (size variation among individuals of the same age) in group memberships of three and 12 fish per tank was minimal when compared to intermediate memberships (six fish per tank). In addition, small fish held in tanks with fish of intermediate sizes demonstrated higher growth when compared to small fish housed with large individuals. Some behaviours, specifically activity and scramble feeding, were more elevated in large group memberships when compared to groups with fewer members. Activity was also found to increase over time during size disparity testing. Results suggest that HSB are ideally suited for high-density, intensive aquaculture since they appear to thrive in high group memberships of similar starting sizes and when a sufficient amount of feed in administered.