Enhancing tilapia intestinal health and growth: Response surface methodology-optimized Schizochytrium limacinum and Lactococcus lactis supplementation

To improve the growth of genetically improved farmed tilapia (GIFT), the supplementation of Schizochytrium limacinum and Lactococcus lactis was sequentially optimized by a single-factor method and central composite design combined with response surface methodology (CCD-RSM) using a developed desirability function (Df) as the response value. The optimum supplementary prescriptions obtained by the single-factor method and CCD-RSM were alone 1.5% S. limacinum, alone 1 × 10⁷ CFU/g L. lactis, and 1.22% S. limacinum + 4.01 × 10⁷ CFU/g L. lactis respectively. The Df of the tilapia fed with the diets supplemented with these optimum prescriptions were 0.53, 0.54, and 0.61, respectively. The Df, weight gain rate (WGR), and feed conversion rate (FCR) of the tilapia fed with the optimum prescriptions obtained by CCD-RSM were significantly higher than those of the tilapia fed with the diets obtained by single-factor experiments and the basic diet for 28 days. Furthermore, the results of CCD-RSM can show that there were significant interactive effects between S. limacinum and L. lactis on trypsin, α-amylase, lipase, total cholesterol (TC)⁻¹ and low-density lipoprotein cholesterol (LDL-C)⁻¹, and Df, but those of single-factor method cannot.