Influence of poultry meal, meat meal or soybean meal inclusion on weight gain and production characteristics of Australian snapper Pagrus auratus

Two experiments were done to evaluate the effects of poultry meal (PM), meat meal (MM) or solvent-extracted soybean meal (SBM) inclusion on the performance of Australian snapper Pagrus auratus. In each experiment, test feeds were formulated with similar contents of digestible protein (DP) and digestible energy (DE) using previously determined digestibility coefficients for this species. In experiment 1, groups of snapper (initial weight 14 g) were fed 4 feeds containing 360, 480, 610 or 730 g kg⁻¹ PM; 3 feeds containing 345, 320 or 500 g kg⁻¹ MM; 3 feeds containing 420, 600 or 780 g kg⁻¹ SBM. In experiment 2, groups of snapper (initial weight 87 g) were fed 3 extruded test feeds that contained combinations of PM, MM, SBM or blood meal (BM) which replaced all but 600, 250 or 160 g kg⁻¹ of fishmeal in respective diet formulations. Both experiments included a proprietary extruded aquafeed (COM) to benchmark fish performance. In experiment 1, weight gain was highest in snapper fed feeds containing 360, 345 or 420 g kg⁻¹ of PM, MM or SBM, respectively, and was similar (P > 0.05) to snapper fed the COM feed. Nonetheless, weight gain and protein retention efficiency tended to decrease as the amount of each test ingredient was increased. Relative feed intake was not affected by the inclusion level of PM, MM or BM, but declined significantly in snapper fed diets containing 600 or 780 g kg⁻¹ SBM. Feeding behaviour indicated fish found these feeds unpalatable. In experiment 2, the harvest weight of snapper fed the 3 extruded test feeds was similar (P > 0.05), but lower than snapper fed the COM feed (i.e. 234 vs. 256 g). Feed conversion ratio (FCR) was best in snapper fed the COM feed (FCR = 1.53); however, the FCR of snapper fed feeds containing 160 (FCR = 1.66), 250 (FCR = 1.70) or 600 g kg⁻¹ fishmeal (FCR = 1.60) was not different (P > 0.05). Australian snapper will readily accept feeds containing high levels of PM, MM or SBM and feeds containing these ingredients will support rapid weight and protein gain with little affect on whole body composition. In combination, these feed ingredients were able to replace all but 160 g kg⁻¹ of fishmeal in an extruded test feed. As such, they serve as valuable alternatives to fishmeal and extend the manufacturing options available to aquafeed producers.