Effects of egg treatment with antioxidants/antiseptics on the larval immunological indices of Trachinotus blochii and characterization of relevant immune gene

Abstract

The Silver Pompano, Trachinotus blochii, is a promising marine species for aquaculture. This study entitled "Evaluation of the effects of egg exposure to antioxidant/antiseptic solution on the immunological indices of Trachinotus blochii larvae and characterization of relevant immune gene " aimed to analyze the impact of egg treatment with glutaraldehyde and hydrogen peroxide on the egg hatching rates, larval immunology, growth, and survival of T. blochii with a final objective of finding out an optimal strategy for larviculture practices. Results showed that 40 ppm glutaraldehyde for 5 min, 400 ppm hydrogen peroxide for 10 min, and 20 ppm iodophor for 9 min were optimal for T. blochii. The optimal concentration was evident through the hatching rates, decreased microbial counts, and survival rates. The results showed a significantly higher hatching rate with glutaraldehyde treatment, whereas all other treatments were remarkably similar. The survival rates were 27.46%, 25.75%, 20.59%, and 19.19% in hydrogen peroxide, glutaraldehyde, iodophor, and negative control tanks. Evaluation of innate immune parameters showed that all treatments caused significantly higher protein content, catalase activity, and superoxide dismutase activity compared to the control. Among the evaluated treatments, iodophor- treated fish showed the maximum protein concentration, catalase activity, and SOD activity, followed by hydrogen peroxide and glutaraldehyde-treated fish. In brief, this research showed that significant improvements in hatching rates and larval survival could be obtained by using optimal chemicals at optimal concentration and exposure duration for egg disinfection of marine fish. Toll-like receptor 21 (TLR21) is a non-mammalian TLR playing an essential role in the innate immunity of fish, amphibians, and birds. The study's second objective was to get the complete sequence of the TLR21 gene from T. blochii. The entire length of TLR21 cDNA was 3171 bp, containing a 5' untranslated region and a 3' poly tail. The ORF length was 2931 bp, encoding 976 amino acid residues. The nucleotide and amino acid sequence showed maximum similarity with Trachinotus ovatus. Phylogenetic tree analysis showed the clustering of the T. blochii TLR21 gene with the other fish TLR21 genes. The sequence showed a typical TLR protein domain structure, including leucine-rich repeat motifs, a transmembrane domain, and a toll/interleukin-1 receptor domain. Strikingly, the TLR21 gene was found as an intron-less gene in T. blochii. The results reference further immune and disease management studies on T. blochii.