Exposure to salinity induces oxidative damage and changes in the expression of genes related to appetite regulation in Nile tilapia (Oreochromis niloticus)

Selection of references for quantitative real-time PCR analysis of microRNAs in Nile tilapia (Oreochromis niloticus) under osmotic stress

MicroRNAs play crucial regulatory roles in various aspects of development and physiology, including environmental adaptation and stress responses in teleosts. RT-qPCR is the most commonly used method for studying microRNA expression, with the accuracy and reliability of results depending on the use of an appropriate reference gene for normalization. This study aimed to evaluate seven miRNAs (U6, Let-7a, miR-23a, miR-25-3, miR-103, miR-99-5, and miR-455) expression stability in different tissues of Nile tilapia subjected to osmotic stress. Fish were divided into two groups: a control and an experimental group, raised in 0 and 12 ppt salinity water respectively. After 21 days, brain, gills, liver, and posterior intestine were collected for analysis. Different mathematical algorithms (geNorm, NormFinder, BestKeeper, and the comparative ΔCt method) were employed to identify the most suitable reference miRNAs. The results indicate that the miR-455/miR-23a combination is a robust reference for normalizing miRNA expression levels in studies of osmotic stress responses in Nile tilapia. The stability of miRNA expression can vary depending on specific stress conditions and biological processes, underscoring the necessity of selecting appropriate normalizing miRNAs for each experimental context. This study identifies reliable reference genes for future RT-qPCR analyses of miRNA expression, thereby enhancing our understanding of molecular responses in fish to environmental challenges. These insights are fundamental to the development of new technologies for the improved management and sustainability of aquaculture practices.

The effects of environmental changes on the endocrine regulation of feeding in fishes

Fishes are exposed to natural and anthropogenic changes in their environment, which can have major effects on their behaviour and their physiology, including feeding behaviour, food intake and digestive processes. These alterations are owing to the direct action of environmental physico-chemical parameters (i.e. temperature, pH, turbidity) on feeding physiology but can also be a consequence of variations in food availability. Food intake is ultimately regulated by feeding centres of the brain, which receive and process information from endocrine signals from both brain and peripheral tissues such as the gastrointestinal tract. These endocrine signals stimulate or inhibit food intake, and interact with each other to maintain energy homeostasis. Changes in environmental conditions might change feeding habits and rates, thus affecting levels of energy stores, and the expression of endocrine appetite regulators. This review provides an overview of how environmental changes and food availability could affect feeding and these endocrine networks in fishes. This article is part of the theme issue 'Endocrine responses to environmental variation: conceptual approaches and recent developments'.

Assessment of oxidative stress biomarkers in the threatened annual killifish Austrolebias charrua exposed to Roundup

This study aimed to analyze the toxic effects of Roundup Transorb® on the endangered Neotropical annual killifish Austrolebias charrua through the assessment of molecular and biochemical biomarkers. The fish were collected in temporary ponds and exposed to environmentally realistic concentrations of the herbicide (5 mg.L-1 for 96 h). The production of ROS, lipid peroxidation, DNA damage, and membrane fluidity were evaluated in the blood cells by flow cytometry. The mRNA expression of the antioxidant-related genes sod2, cat, gstα, atp1a1, gclc, and ucp1 across the brain, liver, and gills was quantified. The acute exposure of annual killifish to Roundup significantly increased ROS production, lipid peroxidation, and DNA damage in their erythrocytes. Likewise, Roundup Transorb® decreased membrane fluidity in the blood cells of the exposed fish. Gene expression analysis revealed that Roundup exposure alters the relative expression of genes associated with oxidative stress and antioxidant defense. Our results give rise to new insights into adaptive mechanisms of A. charrua in response to Roundup. Since Brazilian annual killifishes strongly risk extinction, this study paves the way for developing novel biotechnologies applied to environmental monitoring and aquatic toxicology assessment.

Activation of the growth-IGF-1 axis, but not appetite, is related to high growth performance in juveniles of the Malabar grouper, Epinephelus malabaricus, under isosmotic condition

Salinity, a determining factor in aquatic environments, influences fish growth. Here, we evaluated the effect of salinity on osmoregulation and growth performance in juveniles of the Malabar grouper, Epinephelus malabaricus, a species of high commercial value in Asian markets; we also identified the salinity that maximized this species' growth rate. Fish were reared at 26 °C and under a 14:10 h photoperiod with a salinity of 5 psu, 11 psu, 22 psu, or 34 psu for 8 weeks. Change in salinity had minimal impact on the plasma Na+ and glucose concentrations, although the Na+/K+-ATPase (nkaα and nkaβ) transcript levels in the gills were significantly lower among fish reared at 11 psu salinity. Concomitantly, oxygen consumption was low in fish reared at 11 psu salinity. The feed conversion ratio (FCR) was lower in fish reared at 5 psu and 11 psu salinities than at 22 psu and 34 psu salinities. However, the specific growth rate (SGR) was higher in fish reared at 11 psu salinity. These results suggest that rearing fish at 11 psu salinity would decrease energy consumption for respiration and improve food-conversion efficiency. Among fish reared at 11 psu salinity, the transcript levels of growth hormone (gh) in the pituitary, as well as its receptor (ghr) and insulin-like growth factor I (igf-1) in the liver, were upregulated; these findings suggested stimulation of the growth axis at low salinity. In contrast, there were minimal differences in the transcript levels of neuropeptide Y (npy) and pro-opiomelanocortin (pomc) in the brains of fish reared at any salinity, suggesting that salinity does not affect appetite. Therefore, growth performance is higher in fish reared at 11 psu salinity because of activation of the GH-IGF system, but not appetite, in Malabar grouper juveniles.