Temperature and hypoxia on oxidative stress responses in pacu Piaractus mesopotamicus

Gills de novo assembly reveals oxidative stress, unfolded protein, and immune response on red cusk-eel (Genypterus chilensis) under thermal stress

The heat waves on the South Pacific coast could lead to thermal stress in native fish. The red cusk-eel (Genypterus chilensis) is relevant for Chilean artisanal fisheries and aquaculture diversification. This study examined the effect of high-temperature stress in the gills of G. chilensis in control (14 °C) and high-temperature stress (19 °C) conditions. High-temperature stress induces a significant increase in gills cortisol levels. Additionally, oxidative damage was observed in gills (protein carbonylation and lipoperoxidation). RNA-seq data was used to build the first transcriptome assembly of gills in this species (23,656 annotated transcripts). A total of 1138 down-regulated and 1531 up-regulated transcripts were observed in response to high-temperature stress in gills. The enrichment analysis showed immune response and replication enriched processes (on down-regulated transcripts), and processes related to the folding of proteins, endoplasmic reticulum, and transporter activity (on up-regulated transcripts). The present study showed how gills could be affected by high-temperature stress.

Review: Understanding fish muscle biology in the indeterminate growth species pacu (Piaractus mesopotamicus)

The muscle phenotype of fish is regulated by numerous factors that, although widely explored, still need to be fully understood. In this context, several studies aimed to unravel how internal and external stimuli affect the muscle growth of these vertebrates. The pacu (Piaractus mesopotamicus) is a species of indeterminate muscular growth that quickly reaches high body weight. For this reason, it adds great importance to the productive sector, along with other round fish. In this context, we aimed to compile studies on fish biology and skeletal muscle growth, focusing on studies by our research group that used pacu as an experimental model along with other species. Based on these studies, new muscle phenotype regulators were identified and explored in vivo, in vitro, and in silico studies, which strongly contribute to advances in understanding muscle growth mechanisms with future applications in the productive sector.

Hypoxia stress induces hepatic antioxidant activity and apoptosis, but stimulates immune response and immune-related gene expression in black rockfish Sebastes schlegelii

Dissolved oxygen concentrations both in the open ocean and coast have been declining due to the interaction of global climate change and human activity. Fish have evolved different adaptative strategies to cope with possibly damage induced by hypoxic environments. Black rockfish as important economic fish widely reared in the offshore sea cage, whereas related physiological response subject to hypoxia stress remained unclear. In this study, hepatic anti-oxidant enzymes (superoxide dismutase [SOD], catalase [CAT], glutathione peroxidase [GSH-Px]), aminotransferase (AST) and alanine aminotransferase (ALT) activities, lipid peroxidation (LPO), malondialdehyde (MDA) and glutathione (GSH) content, immunological parameters and the expression of apoptosis (bax, bcl2, p53, caspase3, xiap) and immune-related genes (c3, il-1β, ccl25, saa, hap, isg15) of black rockfish were determined during hypoxia and reoxygenation to illustrate the underlying defense response mechanisms. Results showed that hypoxia stress remarkably increased hepatic LPO and MDA content, AST and ALT activity and proportion of pyknotic nucleus. Hepatic SOD, CAT and GSH-Px activity manifested similar results, whereas GSH levels significantly decreased under hypoxia stress. The apoptosis rate of hepatocyte increased during hypoxia stress and reoxygenation. Meanwhile, p53, caspase3, bax and xiap mRNAs and bax/bcl2 rations were significantly up-regulated under hypoxia stress. However, bcl2 mRNA was significantly down-regulated. Interestingly, hypoxia stress significantly increased NBT-positive cell percent, phagocytic index, respiratory burst and ACH50 activity, and lysozyme activity. The mRNA levels of c3, ilβ, ccl25, saa, hap and isg15 were significantly up-regulated in the liver, spleen and head-kidney under hypoxia stress. The above parameters recovered to normal status after reoxygenation for 24 h Thus, hypoxia stress impairs hepatic antioxidant capacity, induces oxidative damage and apoptosis via the xiap-p53-bax-bcl2 and the caspase-dependent pathways, but enhances host immunity by regulating nonspecific immune indices and related genes expression to maintain homeostasis in black rockfish. These findings will help fully understand the hypoxia tolerance mechanisms of black rockfish and provide more data for offshore open ocean farming.

Transcriptome analysis reveals the early resistance of zebrafish larvae to oxidative stress

Oxidative stress is one of most common environmental stresses encountered by fish, especially during their fragile larval stage. More and more studies are aimed at understanding the antioxidant defense mechanism of fish larvae. Herein we characterized the early resistance of zebrafish larvae to oxidative stress and investigated the underlying transcriptional regulations using RNA-seq. We found that pre-exposure of zebrafish larvae to 2 mM H₂O₂ for 1 or 3 h significantly improved their survival under higher doses of H₂O₂ (3 mM), suggesting the antioxidant defenses of zebrafish larvae were rapidly built under pre-exposure of H₂O₂. Comparative transcriptome analysis showed that 310 (185 up and 125 down) and 512 (331 up and 181 down) differentially expressed genes were generated after 1 and 3 h of pre-exposure, respectively. KEGG enrichment analysis revealed that protein processing in endoplasmic reticulum is a highly enriched pathway; multiple genes (e.g., hsp70.1, hsp70.2, and hsp90aa1.2) encoding heat shock proteins in this pathway were sharply upregulated presumably to correct protein misfolding and maintaining the cellular normal functions during oxidative stress. More importantly, the Keap1/Nrf2 system-mediated detoxification enzyme system was significantly activated, which regulates the upregulation of target genes (e.g., gstp1, gsr, and prdx1) to scavenger reactive oxygen species, thereby defending against apoptosis. In addition, the MAPK, as a transmitter of stress signals, was activated, which may play an important role in activating antioxidant system in the early stages of oxidative stress. Altogether, these findings demonstrate that zebrafish larvae rapidly establish resistance to oxidative stress, and this involves changes in protein processing, stress signal transmission, and the activation of detoxification pathways.