Evaluation of conventional or hydrolyzed stickwater from food-grade skipjack tuna by-product in diet for hybrid grouper (Epinephelus fuscoguttatus ♀ × Epinephelus lanceolatus ♂)

Abstract

The aim of this study was to investigate how dietary conventional (CSW) or hydrolyzed (HSW) stickwater from skipjack tuna by-product affected growth and feed utilization of hybrid grouper. Nine isonitrogenous (500–505 g crude protein (CP) (kg DM)−1) and isoenergetic (20.3–20.9 MJ gross energy (GE) (kg DM)−1) extruded diets were formulated. A control diet (FMC) was produced with 450 g kg−1 inclusion of fish meal (FM), but without stickwater. The other eight diets were made with a 1:1:1 mixture (dry matter based) of soy protein concentrate (SPC), corn gluten meal (CGM), and CSW or HSW replacing 10, 20, 40 and 60% of FM from the FMC diet. The diets were fed to triplicate groups of hybrid grouper 4 times a day for 8 weeks. The fish were raised in a recirculated aquaculture system (RAS) with 25 ppt salinity and 30 °C average temperature. Feed intake (FI) did not significantly (P > 0.05) differ among the dietary treatments. Gradually increased replacement with CSW resulted in linear, negative dose response in weight gain (WG), and a linear positive response in FCR. The hepatosomatic index (HSI) decreased linearly. Whole body CP, lipid and ash, and the apparent digestibility (ADC) of energy and the amino acids Ile and Met decreased in a quadratic manner. Linear, negative responses were seen for the ADC of Lys, Thr, Val, and the sum of essential and total amino acids. Replacing with HSW did not significantly affect WG, FCR, HSI, VSI, whole body dry matter, CP, fat contents, protein- or energy efficiencies. Whole-body ash content showed a negative quadratic response. Factorial ANOVA showed that fish fed HSW grew significantly faster and converted the feed more efficiently than the CSW. There was also a tendency (P = 0.061) that fish fed the HSW diets ate more than the fish receiving the CSW feeds. In conclusion, both feeds with CSW and HSW supported rapid growth and efficient feed conversion of hybrid grouper. Fish fed diets with HSW grew faster and utilized the nutrients more efficiently than did the fish fed diets with CSW.