Effect of dietary iron (Fe) level on growth performance and health status of largemouth bass (Micropterus salmoides)

The aim of this study was to investigate the effects of dietary iron (Fe) levels on the growth performance, health status, meat quality, and intestinal flora of juvenile largemouth bass (Micropterus salmoides) and to determine the dietary Fe requirement of largemouth bass. Largemouth bass was fed with 6 isonitrogenous and isocaloric experimental diets containing Fe levels of 42.26, 50.79, 66.61, 80.86, 123.13, and 201.87 mg/kg for 10 weeks. The results showed that both final body weight (FBW) and specific growth rate (SGR) tended to increase and then decrease with increasing dietary Fe level, reaching their highest values of 50.34 g and 3.58%/d at a dietary Fe concentration of 80.86 mg/kg respectively. Feed efficiency (FE) and protein efficiency ratio (PER) increased linearly with increasing dietary Fe level. Total serum protein (TP) and urea nitrogen (UN) decreased linearly with increasing dietary Fe level. Serum superoxide dismutase (SOD) and catalase (CAT) enzyme activities tended to increase and then decrease with increasing dietary Fe level, while serum malondialdehyde (MDA) level tended to decline and then increase. In addition, increased dietary Fe level tended to improve muscle hardness and chewiness, thus improving meat quality. Analysis of the intestinal flora showed that the abundance of microorganisms such as Plesiomonas, Peptostreptococcaceae, and Lactococcus in the genus level increased significantly at dietary Fe concentrations of 80.86 mg/kg and 201.87 mg/kg, indicating that appropriate levels of dietary Fe can increase the diversity of intestinal microorganisms. Optimal dietary Fe levels for juvenile largemouth bass were determined to be between 73.81 and 83.22 mg/kg based on the broken-line regression analyses of SGR, FE, or hemoglobin content.