Generating transcriptomic resources in the teleost fish black cusk-eel (Genypterus maculatus) to evaluate thermal stress in the liver under a climate change scenario.

The black cusk-eel (Genypterus maculatus) is a native fish that is relevant for traditional Chilean fisheries and has aquaculture potential. However, the genomic information and the biological knowledge related to the effect of thermal stress response are limited. This study generated the first de novo transcriptome assembly of the liver of G. maculatus and investigated the hepatic response to thermal stress in the G. maculatus. The de novo assembly resulted in 26,620 annotated transcripts, with an N50 of 2297, and a GC% of 49.76%. BUSCO analysis showed 97.1% and 75.7% complete orthologous (Metazoa and Actinopterygi, respectively). Functional annotation showed a total of 55,556 GO terms, with 26,128 annotations on biological process, 15,225 annotations on molecular functions, and 14,213 annotations on cellular component. The RNA-seq analysis revealed 94 differentially expressed transcripts in response to thermal stress, with 64 downregulated and 30 upregulated transcripts. The enrichment analysis showed biological processes related to double-strand break repair via homologous recombination, reciprocal meiotic recombination, and DNA repair. A significant increase in cortisol levels with no significant difference activity of hepatic enzymes (ALT, AST, AP) due to thermal stress was observed. Also, an increase in DNA damage (AP sites formation) and lipid peroxidation (HNE protein adducts) in the liver due to thermal stress was observed. The differentially expressed transcripts were validated using qPCR, confirming the RNA-seq results. The findings provide valuable genomic information for G. maculatus and highlight the physiological and molecular responses to thermal stress in the species under the context of climate change.