The influence of density and dominance on Pacific white shrimp (Litopenaeus vannamei) feeding behaviour

Identifying correct stocking densities is an important concern for shrimp farming especially when intensification of shrimp production is growing in order to meet increasing demand. Increased stocking densities generate greater competition among individuals, reduced feeding efficiencies and increased water degradation. Little is known, however, about the effects of stocking density on feeding behaviour and conspecific interactions in commercial shrimp species. Therefore, the aim of the present study was to investigate the effects of density and dominance hierarchies on the feeding behaviour of Pacific white shrimp (Litopenaeus vannamei). Juvenile shrimp (7.91 +/- 1.81 g, n = 56) were divided into three density treatments (low: 6.2 shrimp/m(2), medium: 12.4 shrimp/m(2) and high: 24.8 shrimp/m(2)) with four groups at each density. Groups of shrimp were placed with feed in test arenas and recorded for 20 min, with each group recorded eight times on consecutive days. Video analysis was conducted via automated observation using EthoVision tracking software. Dominance hierarchies were observed within each group and were found to remain stable across observations. Therefore the effect of dominance on feeding behaviour was investigated via comparisons of behaviour of the most dominant and subordinate shrimp in each group. Results showed a clear effect of both density and dominance on L. vannamei feeding. A greater relative feed consumption was observed in shrimp at the high density, even though less time was spent on the feeding area due to space limitations on the feeding tray. Lowest levels of feeding activity were found in the low-density treatments, coupled with higher levels of exploratory behaviour (i.e. moving, distance and velocity) indicative of a reduced feeding motivation. Smaller distances and extended contact times between individuals were found with increasing density. Dominance influenced feeding behaviour; subordinates spent longer on the feeding area whereas dominants explored the test arena more, however, these differences were minimised at high density. Findings from this study therefore revealed how L. vannamei at high density (24.8 shrimp/m(2)) maximized feeding behaviours while minimising feeding inefficiencies due to dominance interactions. The study also showcased tracking shrimp feeding behaviour automatically at a group level.