Dietary Soybean Lecithin Improves Growth, Immunity, Antioxidant Capability and Intestinal Barrier Functions in Largemouth Bass Micropterus salmoides Juveniles

Abstract

This study evaluated the effects of dietary soybean lecithin (SBL) on the growth, haematological indices, immunities, antioxidant capabilities, and inflammatory and intestinal barrier functions because little information of dietary SBL could be obtained in juvenile largemouth bass (Micropterus salmoides). The fish were fed identical diets except for SBL added at 0, 2, 4 and 8%. It was found that 4 and 8% SBL significantly increased fish weight gain and daily growth rate (p < 0.05), while 4% SBL was optimal for enhancing RBC, HGB, PLT, MCV, MCH, WBC and MON in blood, and ALB and ALP in serum (p < 0.05). SBL (4%) also significantly elevated the antioxidant enzymes activities of T-SOD, CAT, GR, GPx, GST and T-AOC and GSH contents; increased mRNA transcription levels of Nrf2, Cu/Zn-SOD, CAT, GR, GST3 and GPx3; and decreased MDA contents. Keap1a and Keap1b levels were markedly down-regulated (p < 0.05). SBL (4%) significantly enhanced levels of the immune factors (ACP, LZM and C3) and the mRNA expression levels of innate immune-related genes (C3, C4, CFD, HEPC and MHC-I) compared with the control groups (0%) (p < 0.05). SBL (4%) significantly increased IgM and T-NOS in the intestine (p < 0.05) and significantly decreased levels of TNF-α, IL-8, IL-1β and IFN-γ and increased TGF-β1 at both transcription and protein levels in the liver and intestine (p < 0.05). The mRNA expression levels of MAPK13, MAPK14 and NF-κB P65 were significantly decreased in the intestine in the 4% SBL groups (p < 0.05). Histological sections also demonstrated that 4% SBL protected intestinal morphological structures compared with controls. This included increased intestinal villus height and muscular thickness (p < 0.05). Furthermore, the mRNA expression levels of the intestinal epithelial cell tight junction proteins (TJs) (ZO-1, claudin-3, claudin-4, claudin-5, claudin-23 and claudin-34) and mucin-5AC were significantly up-regulated in the 4% SBL groups compared with the controls (p < 0.05). In conclusion, these results suggested that 4% dietary SBL could not only improve growth, haematological indices, antioxidant capabilities, immune responses and intestinal functions, but also alleviate inflammatory responses, thereby providing reference information for the feed formulations in cultured largemouth bass.

Effects of Five Lipid Sources on Growth, Hematological Parameters, Immunity and Muscle Quality in Juvenile Largemouth Bass (Micropterus salmoides)

“…Combined with the fatty acid composition and higher expression levels of LZM, HEPC and NRAMP in the FO, SO and RO groups in our results, this indicates that higher n-3PUFA contents in FO, SO and RO could enhance the innate immunity of largemouth bass by up-regulating the levels of these defense effectors [ 70 ]. In addition, HGB and RBC are not only responsible for transporting oxygen, but are also related to better immunity in animals [ 13 , 71 ]. Our results show that there were higher HGB and RBC levels in the RO groups, which suggests that RO could increase the oxygen-carrying capabilities and enhance the innate immunity of largemouth bass.…”

“…This may be due to differences in the fatty acid content of the diet, which in turn has an effect on the growth and metabolic capacity of the fish [ 4 ]. In addition, lots of experiments also found there was a close relationship between animal metabolic abilities and adequate levels of serum biochemical indices [ 12 , 13 ]. Lower alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities could reflect hepatic health status [ 12 ].…”

“…Meanwhile, there was a close relationship between fish immune status and hematological and serum indices including white blood cells (WBC), hemoglobin (HGB), neutrophils (NEU), monocytes (MON), red blood cells (RBC), platelets (PLT), albumin (ALB), lymphocytes (LYM), hemoglobin (HGB), alkaline phosphatase (ALP), etc. [ 12 , 13 ]. Many studies have demonstrated that higher amounts of RBC, WBC, LYM and HGB could reflect better immunity and effectively promote fish health via the hematopoietic system mediated by adequate nutrients [ 13 , 19 ].…”

“…[ 12 , 13 ]. Many studies have demonstrated that higher amounts of RBC, WBC, LYM and HGB could reflect better immunity and effectively promote fish health via the hematopoietic system mediated by adequate nutrients [ 13 , 19 ]. However, little information about the hematological variations could be obtained in largemouth bass fed with different dietary lipid sources up to now.…”

Effects of Five Dietary Carbohydrate Sources on Growth, Glucose Metabolism, Antioxidant Capacity and Immunity of Largemouth Bass (Micropterus salmoides)

“…Blood cell identification and counting were conducted using a TEK 8500 VET automatic blood analyzer (Tekang Technology, Nanchang, China) following methods described by Wu et al [18]. Metabolite contents and enzyme activities in the serum samples were detected on C400n automated hematology analyzer (Shenzhen, China) according to the corresponding instructions described by Yang et al [17].…”