ABSTRACT
Microbes are the most significant ubiquitous pathogens that cause serious infections in freshwater fish, leading to tremendous economic losses. The present study was designed to investigate the extent of changes in cytokine expression, hemato-biochemical parameters, and tissue histology of Cirrhinus mrigala (C. mrigala) challenged with Pseudomonas aeruginosa (P. aeruginosa) and Fusarium oxysporum (F. oxysporum). Fish were divided into three major groups: control, P. aeruginosa-challenged, and F. oxysporum-challenged. The infection in both challenge assays was allowed to progress until 7 days post infection. Upregulated expression of TNF-α and IL-1ß was found in blood, gills, livers, and kidneys of the challenged fish. Significant differences were noted in hematological parameters of challenged fish. Alanine aminotransferase, aspartate aminotransferase, and alkaline aminotransferase levels also showed significant differences in infected and control groups. An increase in serum albumin and globulin and a decrease in total protein were noted in infected groups as compared to the control group. Severe histological alterations were noted in gill, liver, and kidney tissues of the infected groups as compared to control. The order of histological alteration index for P. aeruginosa challenge was liver > kidney > gills, and for F. oxysporum challenge it was kidney > liver > gills. These changes in fish infected by P. aeruginosa and F. oxysporum can be used as an effective and subtle index to monitor the physiological and pathological conditions of fish.
ABSTRACT
Probiotics play a significant role in aquaculture by improving the growth, health, and survival rate of fish against pathogenic organisms. In the present study, we have evaluated the effects of a Lactobacillus rhamnosus (L. rhamnosus) probiotic on growth performance and disease resistance in Oreochromis niloticus (O. niloticus) fingerlings. Four different concentrations of L. rhamnosus (T1: 0.5 × 1010, T2: 1 × 1010, T3: 1.5 × 1010, and T4: 2 × 1010 CFU/kg feed) were administered to fish over a period of three months. L. rhamnosus treated fish revealed a high growth increment as compared to the control, and the values of macromolecules (amino acids, fatty acids, and carbohydrates) varied significantly among the treated and control groups. Levels of thyroid hormones were noted to be high in the probiotic-treated groups. A challenge assay was performed with Aeromonas hydrophila (A. hydrophila). The optimum calculated concentration of probiotics from the growth assay (1.5 × 1010 CFU/kg feed) was used for the challenge assay. Fish were divided into four groups as follows: control (Con), probiotic-treated (PL), infected (I), and infected + probiotic-treated (I + PL) groups. Significant variations in hematological parameters were observed among control and treated groups. Histopathological changes were recorded in infected fish, while the infected + probiotic-treated group showed less deformations indicating the positive effect of the probiotic supplementation. The survival rate of fish was also better in the probiotic-treated group. Based on these findings, we conclude that probiotic supplementation enhances the growth and improves immunity of O. niloticus. Therefore, we propose that probiotics can be used as promising feed supplements for promoting fish production and disease resistance in aquaculture.
