Cage Production of Red Drum Weaned From Trash Fish to Extruded Feed at Sub-Market Size
Weaning of 172-g red drum (Sciaenops ocellata) from trash fish to extruded feed, followed by growout to market size on extruded feed, was demonstrated in a cage feeding trial at Longmen Town, Qingzhou City, Guangxi Province, China. Red drum that had only been fed with trash fish were stocked in three, 6.4-m3 cages at a density of 156 fish per m3 and weaned from trash fish to a 35% soymeal extruded feed over a period of one week. After weaning to extruded feed, red drum were fed to satiation twice daily with a 43/12 extruded, floating marine fish feed formulated by ASA. Red drum grew from 172 g to 666 g in 86 days on the ASA feed, with an average FCR of 1.68:1. Average fish carrying capacity at harvest was 53 kg/m3 of cage. The average fish survival rate was 51.5%. Net economic return and return on investment for the trial were RMB 149/m3 and 21.1%, respectively. The trial demonstrated that sub-market size red drum could be weaned from trash fish to extruded feed without difficulty. Feed conversion efficiency with the ASA 43/12 feed in this trial was not as good as in other red drum trials, but was still significantly better than that obtained in the area with trash fish. Feed cost per kilogram of fish growth with the ASA extruded feed was RMB 8.06, which was substantially below the cost of producing red drum with trash fish. Low water salinity at the trial site significantly impacted red drum growth performance, feed conversion efficiency and survival. Red drum exhibited a low tolerance to fluctuating salinity conditions that prevailed at the site throughout the feeding trial. Salinity ranged from 0 ppt to 14 ppt, with rapid fluctuations. The Longmen site was assessed to be a high-risk production site for red drum. It is recommended that cage fish farmers in the Longmen area focus on species with higher tolerance for low and fluctuating salinity, such as red tilapia and Japanese sea bass.