Utilisation of carbohydrate by yellowtail kingfish Seriola lalandi

This study describes a series of glucose tolerance experiments (GTT) and a feeding trial that were designed to improve the understanding of carbohydrate (CHO) utilisation in juvenile yellowtail kingfish Seriola lalandi. The GTT experiments involved the oral or intravenous administration of d-glucose or the oral administration of pregelatinised wheat starch (PGWS) to fish followed by measurement of blood glucose. The feeding trial was designed to investigate the protein sparing effect of CHO by feeding juvenile fish a series of diets that contained between 10 and 40% PGWS, 10–40% extruded wheat (EW) or 10–40% diatomaceous earth under a restricted feeding regime. Yellowtail kingfish suffered from prolonged hyperglycaemia after being injected or fed d-glucose. Peak response, area under curve (AUC) and duration of hyperglycaemia were also dependent on d-glucose dose rate. Feeding yellowtail kingfish a complex CHO such as PGWS did not increase the AUC response more so than control diets that were virtually devoid of CHO. Based on measures of weight gain and protein efficiency ratio, juvenile fish were able to utilise a limited amount of EW or PGWS to support growth when fed according to a restricted feeding strategy. This response was evidence of a moderate protein-sparing effect of these CHOs. Results from the feeding study indicate that inclusion of typical CHOs such as wheat and wheat starch in commercial feeds at dietary levels higher than 10% will compromise fish performance. ► The ability of Seriola lalandi to utilise carbohydrate was tested. ► Intraperitoneal injection of glucose caused prolonged hyperglycaemia. ► Feeding glucose caused prolonged hyperglycaemia. ► Extruded wheat or gelatinised wheat starch had a moderate protein-sparing effect. ► Weight gain and feed conversion was negatively affected by carbohydrate.