Solid-state fermented fish silage enhances nutritional performance, immune response, and intestinal histomorphology in juvenile European sea bass (Dicentrarchus labrax) fed plant protein diet

IntroductionThis study evaluated the nutritional, physiological, immunological and histomorphometric effects of different solid-state fermented fish silages in juvenile European sea bass (Dicentrarchus labrax) fed a plant-protein-based diet for 70 days.MethodsFish byproduct silage made from the redbelly tilapia (Coptodon zillii) were tested as the control group T1, four solid-state fermented silage; with acidic acid fish silage T2, Lactobacillus plantarum as an inoculum T3, Effective microorganisms® (Em®) T4, and with rumen fluid T5 raised in 15 net cages (0.7 × 0.7 × 1.0 m) with initial weigh 35.0±0.6 g fish. Initial proximate analysis of fish silage showed 42.63% protein and 18.02% lipid.ResultsSolid-state fermented fish silage T3, T4 and T5 had greater concentrations of monounsaturated fatty acids, polyunsaturated fatty acids, and total saturated fatty acids. The T3 consistently exhibited the highest concentrations of key amino acids, including aspartic acid, glutamic acid, glycine, alanine, methionine, and lysine. All solid-state fermented silages have aflatoxin levels below the permissible limit (<20 ppb) and the lowest treatment (P < 0.05) was T3. Also, decreased (P < 0.05) in total microbial load and coliform count (4.0 log₁₀ CFU/g) in T2 and T3 compared to all groups. Results indicated that the T2, T3 and T4 groups showed significantly superior growth performance and feed utilization. Fish body composition from T2, T3 and T4 showed the highest protein and lipid levels and the lowest ash content. Serum total protein (TP) and globulin (GLO) levels were significantly the highest in T3, while liver enzymes (ALT, AST, ALP) and renal markers (creatinine, uric acid) were insignificantly the lowest. Digestive enzyme activity (amylase, protease, lipase) was significantly enhanced in the T3 group. Quantitative morphometric analysis of D. labrax intestinal villi showed that T3 had the greatest villus height, height-to-width ratios and absorptive surface area. Histological examination of the solid-state fermented groups liver tissue showed well-preserved polyhedral hepatocytes with cord-shaped vesicular nuclei and normal hepatic sinusoids.ConclusionL. plantarum fermented silage with plant protein diet improves growth, feed efficiency, immunological indicators and intestinal histomorphometry of juvenile sea bass.