Protecting deleterious effects of high stocking density of Nile tilapia, Oreochromis niloticus using dietary microalgae Golenkinia longispicula: Growth, immune-oxidative markers and associated gene expression

Abstract

Microalgae have been capably used as additive to boost the fish performance and welfare because of their unique nutritional properties and functional bioactive compounds. Thus, factorial experimental design (4 × 2) investigated the effect of dietary dried Golenkinia. longispicula (0.0, 5, 10 and 15 g kg−1 diets) supplementation used in Nile tilapia, Oreochromis niloticus on growth, feed efficiency, hematological, biochemical parameters, antioxidant activity, immunity, and associated gene expression reared under two stoking densities 100 fish m3 (SD100) and 200 fish m3 (SD200). Fingerlings (initial weight of 3.29 ± 0.16 g) were randomly assigned into twenty-four fiberglass tanks (0.5 m3; 250 L volume of water) in triplicate for each treatment at two stocking density SD100 and SD200 for 90-days. Three times per day at 9:00 a.m., 11:00 a.m., and 2:00 p.m., four isonitrogenous (32.89 g kg−1 CP) and isocaloric (17.86 MJ kg−1 GE) diets were given to experimental fish. After 90 days of the feeding trial, the results demonstrated final body weight (FBW), weight gain (WG), specific growth rate (SGR), and feed conversion ratio (FCR) were significantly (P < 0.05) improved by a diet contained 15 g kg−1 G. longispicula reared under SD100. The highest hematocrit (Hct), hemoglobin (Hb), red blood cells (RBCs) levels were detected in the fish-fed diet that had 15 g of G. longispicula kg−1 under SD100 or SD200. No significant differences (P < 0.05) were found in alanine amino transferase (ALT) and aspartate amino transferase (AST) among treatment groups. While adding G. longispicula at SD200 had a substantial (P < 0.05) impact on total protein (TP), Albumin, or growth hormone. The values of immunoglobulin M (IgM), complement component 4 (C4), complement component 3 (C3) and growth hormone (GH) was higher in fish fed a diet that included 15 g kg−1 G. longispicula kg−1 diet under SD100. The maximum activity of glutathione (GSH), glutathione peroxidase (GPX), superoxide dismutase (SOD), and catalase (CAT) was found in a fish-fed diet supplemented with 15 g G. longispicula kg−1 diet under SD100 (P < 0.05) as well as the related hepatic gene expression superoxide dismutase 2 (SOD2), catalase (CAT), and glutathione peroxidase (GPX). The malondialdehyde (MDA) value was lowest when fish were stocked at SD100 or SD200 and 10 g of G. longispicula kg−1 was added to their diet. Fish raised at SD100 or SD200 and fed diets containing 15 g kg−1 G. longispicula were substantially up-regulated the gene expression of the interleukin-1β (IL-1β) and interleukin-8 (IL-8) (P < 0.05). Based on these conclusions, adding G. longispicula up to 10 or 15 g kg−1 to a basal diet ameliorates and enhances growth performance, feed efficiency, immune responses, hepatic antioxidant enzyme, and related immune-antioxidant genes expression and imparts resistance to SD200 stress in Nile tilapia.