Optimized formula for the hybrid abalone Haliotis discus hannai♀ × H. fulgens♂: Betaine supplementation increases the use of rice bran meal as a replacement for kelp

Two trials were conducted to determine the optimal replacement level of rice bran meal (RBM) as a substitute for kelp meal (KM) in the diet of the hybrid abalone Haliotis discus hannai ♀ × H. fulgens ♂. This study also investigated whether betaine as an attractant supplementation could be used to facilitate RBM as a replacement for KM. In Trial 1, RBM was used to replace 25%, 50%, and 100% of the dietary KM (RBM25, RBM50, and RBM100, respectively) based on a diet containing 30% KM (Con). In Trial 2, RBM50 was the same as in Trial 1, and betaine was supplemented in RBM50 at 0.2% (B1), 0.4% (B2), and 0.8% (B3) in the diets. Abalone (weight approximately 4 g) were randomly assigned to four groups replicated in triplicate (60 abalone/replicate). The abalone were fed the experimental diets for 10 weeks. In Trial 1, compared to the Con group, no significant differences were observed in final weight (FW), final shell length (FSL), specific growth rate (SGR), or daily increment in shell length (DISL) at 25% KM replacement by RBM. However, 50% KM replacement significantly reduced the FW, FSL, SGR, and DISL compared to the Con group. There were no significant differences in the proximate composition of the soft body tissues of the abalone. In Trial 2, growth performance parameters of the hybrid abalone were significantly improved with increasing levels of betaine in the diets compared to those fed diet RBM50, reaching the maximum value in the B2 group. Consistent with the feed intake results, the hormone concentrations of neuropeptide Y (NPY) and orexins in the digestive gland and cerebral ganglia of abalone were significantly increased when the supplementation level of betaine in the diets was increased to 0.2%. However, no apparent impacts were observed on NPY or orexin concentrations among the B1, B2, and B3 groups. Finally, we suggest 0.4% betaine supplementation along with replacing 50% of the KM with RBM in the hybrid abalone diet. The optimal diet is a cost-effective alternative feed formulation that can reduce the dependence on KM for abalone production in China. This study also demonstrates the potential of betaine as a feed attractant in abalone aquaculture. •25% kelp meal (KM) can be replaced by rice bran meal (RBM) without obvious adverse impacts on the growth performance of the hybrid abalone.•The addition of 0.4% betaine in diets increased the replacement level of KM by RBM to 50% without negatively affecting the growth performance of the hybrid abalon