Effects on growth metrics, fillet composition, and health biomarkers of juvenile striped catfish (Pangasianodon hypophthalmus) when commercial feed is replaced with graded levels of restaurant food waste

Food waste (FW) is a source of inexpensive and readily available nutrients that can be used as animal feed. However, the use of FW in fish feed is limited. In this study of juvenile striped catfish (Pangasianodon hypophthalmus), commercial feed (CD, 34.1% protein and 4.69% lipid based on dry weight) was replaced with graded levels (25, 50, 75, and 100%) of FW (20.3% protein and 14.9% lipid based on dry weight). The dry weight dietary contents of crude protein (32.8 to 19.9%), crude fiber (4.62 to 1.06%), and ash (9.00 to 3.32%) decreased with FW replacement levels, whereas contents of crude lipid (4.69 to 14.5%) and nitrogen-free extract (48.9 to 61.2%) increased. Fish (3.40 +/- 0.01 g body weight) were assigned to five treatments, each comprising three tanks (60 cm width x 80 cm length x 45 cm height, 100 L water) containing 15 fish each. They received the experimental diets twice daily (09.00 and 16.00 h) at 3% of body weight over an 8-week feeding trial. At the end of the feeding trial, growth performance, feed utilization, digestive enzyme activities, fillet qualities, carcass composition, and hematological parameters, along with an economic analysis, were used as assessment criteria for a suitable diet. The gradual reduction in growth performance was observed as the proportion of FW increased (P < 0.05), and only the fish that received a diet containing 25% FW showed similar specific growth rates (1.60% body weight day(-1)) and feed conversion ratios (1.37 g feed g gain(-1)) to fish that received a diet without FW (P > 0.05). Higher replacement levels had negative effects on these parameters and increased dry matter apparent digestibility coefficients (from 74.0 to 82.2%), while reducing the protein digestibility coefficients (from 85.8 to 67.9%, P < 0.05). Activities of amylase, cellulase, pepsin, trypsin, chymotrypsin, lipase, and the amylase to trypsin ratio were modulated differently across the dietary treatments. The diet containing 25% FW showed no adverse effects on fillet qualities, carcass composition, and hematological parameters. The cost of a diet containing 25% FW (0.71 USD kg(-1)) was lower than the cost of the commercial feed (0.94 USD kg(-1)), albeit not statistically significant (P > 0.05). These findings indicate that replacing 25% of commercial feed with FW could reduce feed costs and mitigate the environmental difficulties of FW disposal.