Abstract
Simple SummaryProbiotics are live microbial adjuncts with numerous beneficial effects on fish. This study aims to evaluate the roles of Aspergillus oryzae (ASP) in the modulation of serum haemato-biochemical measurements, immunity, antioxidative capacity, and transcriptomic responses of Nile tilapia juveniles exposed to salinity stress. Findings revealed that dietary supplementation with A. oryzae mitigated the harmful influences of salinity stress on the exposed Nile tilapia.Nile tilapia Juveniles (19.50 ± 0.5 g) were fed on a basal diet (control group (CTR)) and a diet supplemented with 1 g Aspergillus oryzae (ASP) per kg diet for 12 weeks. Fish were then subjected to different salinity levels (0, 10, 15, and 20 practical salinity units (psu)) for another 15 days. Two-way ANOVA analysis revealed that the individual effects of ASP in Nile tilapia exposed to salinity levels presented a significant decrease (p < 0.05) in values of haemato-biochemical indices (such as glucose, cortisol, alanine transaminase, aspartate transaminase, and malondialdehyde) compared to those in the CTR group exposed to the same salinity levels. Moreover, significant increases (p < 0.05) of blood protein profile (albumin, globulin, and total protein), non-specific immune responses (lysozyme activity, phagocytic activity, and phagocytic index), and antioxidant enzymes activities (glutathione peroxidase, catalase, and superoxide dismutase) were observed in ASP-supplemented groups. Interestingly, there was significant (p < 0.05) downregulation of the mRNA expression values of heat shock protein 70 and interferon-gamma genes, alongside upregulation of the mRNA expression values of interleukin 1 beta and interleukin 8 genes, in the hepatic tissues of Nile tilapia in ASP-supplemented groups exposed to different salinities compared to those in the CTR group exposed to the same salinity levels. Taken together, these findings supported the potential efficacy of dietary supplementation with ASP in alleviating salinity stress-induced haemato-biochemical alterations, immune suppression, and oxidative stress in the exposed Nile tilapia.
Highlights
Over the past decade, the production rates of Nile tilapia (Oreochromis niloticus) have been greatly increased because of increased consumer preferences, relatively reasonable prices, and to some extent, its resistance to diseases [1]
The opposite trend was, noticed in the Aspergillus oryzae (ASP)-supplemented group, which was exposed to the same salinities, whereas the individual effects of ASP in Nile tilapia exposed to different salinity levels showed a significant decrease in blood GLU, CORT, alanine transaminase (ALT), and aspartate transaminase (AST) values (p < 0.05; Table 1), alongside a significant increase in ALB, GLO, and TP values (p < 0.05; Table 1) compared to the CTR group exposed to the same salinity levels
In the present study, compared to the CTR group exposed to different salinity levels, the effects of ASP-supplemented diets in Nile tilapia exposed to the same salinities showed a significant increase in the serum LYZ activity and phagocytic capacity of the macrophages (PA % and phagocytic index (PI)). These findings suggest the immune-modulating roles of dietary ASP against the salinity stress-induced decline in the non-specific immunity of exposed Nile tilapia
Summary
The production rates of Nile tilapia (Oreochromis niloticus) have been greatly increased because of increased consumer preferences, relatively reasonable prices, and to some extent, its resistance to diseases [1]. Finding safe and environmentally friendly alternatives to improve fish health and productivity is of great interest to several researchers [4,5]. Probiotics are live microbial adjuncts that present several beneficial effects to a host, such as improving feed efficiency, enhancing growth performance, and fortifying the host immunity of fish against challenging environmental conditions [6]. The proficiency of probiotics to promote the health status is closely linked to their capability to augment the fish immunity and prevent the growth of pathogenic bacteria [7].
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