THE EFFECT OF DECREASED RATION ON FEEDING HIERARCHIES IN GROUPS OF GREENBACK-FLOUNDER (RHOMBOSOLEA-TAPIRINA, TELEOSTEI)

The aims of the present study were to investigate food consumption, gr owth and the dynamics of feeding hierarchies in the same groups of juv enile greenback flounder (Rhombosolea tapirina: Teleostei) fed either high or low rations. Differential food consumption by individual green back flounder held in groups of 20 showed the presence of feeding hier archies in which individuals consumed between 0 and 22% of the availab le food. Inter-individual differences in food consumption resulted in different growth rates leading to growth depensation (measured as an i ncrease in the coefficient of variation for weight). Intra-individual differences in food consumption tended to be larger for flounder which consumed a lower share of the available food. When the group ration w as reduced the inter-individual and intra-individual variations in foo d consumption increased. Consequently, the relationship between inter- individual and intra-individual variation in food consumption tended t o become stronger at lower food availability and indicated an increase in the strength of the feeding hierarchies. This study suggests that individual differences in food consumption, mediated through exploitat ion competition, contribute to growth depensation in this species of f latfish.