Evaluation of sulfur amino acid and zinc supplements to soybean-meal-based diets for hybrid striped bass

Hybrid striped bass (Morone chrysops × M. saxatilis) aquaculture is a major commercial enterprise in the United States and internationally. Efforts to decrease diet costs and limit dependence on fishmeal have led to the development of plant-based diets as alternative aquafeeds. Due to limiting concentrations of some amino acids such as methionine and cystine, in plant meals such as soybean meal, supplementation of plant-based diets with methionine or other sulfur amino acid compounds may be required. High levels of soybean meal also may reduce the bioavailability of minerals such as zinc due to the inhibitory effects of phytate. Therefore, the current study was conducted to evaluate different sulfur amino acid and zinc supplements in soybean-meal-based diets with hybrid striped bass for possible refinement of diets and reduction of production costs.In the first feeding trial, a basal soybean-meal-based diet (56% soybean meal and 15% fishmeal) marginally deficient in total sulfur amino acids (TSAA) (1.10% methionine and cystine) was supplemented with either l-methionine, methionine hydroxyl analog (MHA) calcium salt or Mintrex® (liquid MHA with chelated zinc) and fed to triplicate groups of juvenile hybrid striped bass for 10 weeks. The different methionine supplements provided similar weight gain, feed efficiency ratio (FER) and protein efficiency ratio (PER) values that tended to be greater than observed in fish fed the basal diet. Mintrex® supplementation provided much higher plasma zinc concentrations compared to fish fed the other methionine supplements.In additional feeding trials, a soybean-meal-based control diet containing l-methionine to satisfy the requirement for TSAA was supplemented with varying concentrations of zinc sulfate or Mintrex®, each to provide 5, 10, and 20 μg Zn/kg diet, and fed to juvenile hybrid striped bass. The different zinc concentrations did not affect zinc integration into the scale or bone of hybrid striped bass after 8 weeks of feeding. Zinc from zinc sulfate in comparison to Mintrex® was absorbed slightly but significantly better based on postprandial serum zinc concentrations of fish fed the two products at the same dietary zinc concentration; however, these absorption differences did not affect long-term zinc deposition in the scale and bone.