Bioenergetics of cannibalism in juvenile barramundi Lates calcarifer (Bloch): exploring growth advantage of fish fed live prey and formulated diet

The present study investigated the growth performance of juvenile barramundi Lates calcarifer (Bloch) fed conspecific prey (CP), formulated diet (FD) and a mix of both (MIX) using a bioenergetics approach. Fish in the MIX treatment ingested significantly more CP than FD by dry mass. However, prey mass ingestion and cannibalism rate in the MIX treatment were significantly lower than in the CP treatment. This indicates that the provision of alternative food does not complete mitigate cannibalism, but it can significantly reduce cannibalism in barramundi. Fish in the FD treatment showed a significantly higher daily food intake than fish in the CP or MIX treatments. However, fish fed conspecifics showed significantly better feed conversion efficiencies, apparent digestibility rates and growth performances. Exclusive cannibalistic barramundi assimilated significantly more energy consumed, with 1.5% of energy lost in faeces comparing with 7.3% of siblings feeding exclusively on FD. Consequently, exclusive cannibals channelized more energy consumption into growth (57.1%) than those fed solely on FD (43.9%). Therefore, high energy allocation into growth promoted better feed conversion efficiency and growth performance of cannibalistic barramundi than siblings fed solely on FDs. This study implies that fast-growing cannibals may continuously prey on slow-growing conspecifics due to growth advantage through cannibalism. Therefore, size heterogeneity should be reduced at initial stocking and controlled as fish grow to avoid the emergence of new cannibals.