Feeding strategy changes boldness and agonistic behaviour in the swimming crab ( Portunus trituberculatus )

Abstract

Agonistic behaviours and cannibalism are key factors that restrict increases in the production of crab aquaculture. To explore the effects of feeding strategies on the boldness, agonistic behaviour and physiological response of swimming crab (Portunus trituberculatus), three treatment groups were established (feeding once a day:S0, every 3 days: S3 and every 6 days:S6). The intensity and duration of fighting, and agonistic behaviours were compared. The hepatosomatic index and the concentration of glycogen, glucose and lactate were also measured. The main results were as follows: (1) With an increase in time between feeding, boldness, duration and intensity of fighting increased first, then decreased, reaching a maximum in the S3 group, and this was significantly higher than in the S6 group. (2) Agonistic behaviour increased first and then decreased. The ‘move to’, ‘cheliped display’ and ‘contact behaviours’ of crabs in the S3 group were significantly higher than the S6 group; (3) Before fighting, with the increase in feeding time, the hepatosomatic index, glycogen and glucose concentration of crabs decreased, and these indicators were significantly higher in the S0 group than in the S6 group. (4) After fighting, the glucose and lactate concentrations were significantly greater than those before fighting. These results suggest that both boldness and feeding strategy can affect the agonistic behaviour of crab. Short-term reductions in food resources promoted inter-individual fighting, and bold individuals were more likely to win battles. However, a long-term decrease in food resources reduced fighting among individuals.