Effects of Different Corn Starch Levels on Growth, Protein Input, and Feed Utilization of Juvenile Hybrid Grouper (male Epinephelus lanceolatus x female E. fuscoguttatus)

An 8-week growth trial was conducted to study the effects of different corn starch levels on growth and feed utilization of juvenile hybrid grouper (male Giant Grouper Epinephelus lanceolatus x female Brown-marbled Grouper E. fuscoguttatus). Five isonitrogenous (48% crude protein, dry weight basis) and isolipidic (10% crude lipid, dry weight basis) diets were formulated to contain 0, 7, 14, 21, or 28% corn starch, respectively. Each dietary treatment had three replicates. Groups of 22 hybrid grouper juveniles (average initial weight, 2.74 g/fish) were stocked into small floating cages (120 cm long x 70 cm wide x 50 cm high). Triplicate groups of fish were fed each dietary treatment twice daily (0800 and 1600 hours) to apparent satiation. Water quality was monitored daily. Weight gain (WG) of hybrid grouper displayed no significant differences among all experimental groups. Fish fed 0% corn starch had significantly higher daily protein intake than fish fed 7, 14, 21, and 28% corn starch. The feed conversion ratio (FCR) and daily feed intake (FI) were significantly higher in fish fed diets with 0% corn starch, but FCR and FI were not observed to vary among fish fed any of the other experimental diets. Fish fed 0% corn starch had a lower protein efficiency ratio (PER) than fish fed other experimental diets, and the differences were significant when compared with fish fed 21% or 28% corn starch. Intraperitoneal fat (IPF) ratios did not show significant variations among all experimental treatments. The hepatosomatic index (HSI) of fish fed 0% corn starch were significantly lower than that of fish fed 14, 21, and 28% corn starch. Whole-body moisture, protein, lipid, and ash contents as well as musclemoisture, protein, and lipid contents showed no significant differences among all experimental groups. Hepatic glycogen content increased as dietary corn starch level increased. Fish fed the diet with no corn starch had more protein content in the liver than fish fed 14, 21, or 28% corn starch. Generally, supplementations of 7-28% dietary corn starch could reduce dietary protein input and improve feed utilization of hybrid grouper without negatively affecting their growth.