Chile is the second-largest producer of Atlantic salmon (Salmo salar), a key industry facing challenges such as infestations by Caligus rogercresseyi, which cause significant economic losses. However, there are no studies exploring how environmental variables in marine culture centers affect salmon’s immune response, considering their poikilothermic characteristics. This study analyzed the effect of the seasonal temperature on the skin transcriptome of Atlantic salmon infested with C. rogercresseyi in fjord-based farms in the Aysén Region during autumn and spring. Two different centers were analyzed (autumn: Farm-A; spring: Farm-S) to ensure the same age of the fish sampled in each season. RNA sequencing (RNA-seq) and functional network analysis revealed notable seasonal transcriptomic differences. In autumn, 253 differentially expressed genes (DEGs) were found, primarily associated with stress response and negative regulation of T-cell proliferation, suggesting an impaired response against the ectoparasite. In spring, 103 DEGs were detected, associated with protein synthesis and the activation of immune mechanisms, including complement activation, granulocyte chemotaxis, and antigen presentation. This is the first study to evaluate the transcriptomic response of healthy skin in C. rogercresseyi-infested salmon under farming conditions, highlighting the importance of considering seasonal variations for the development of more effective management strategies in the aquaculture industry.

Heat shock proteins (HSPs), particularly HSP70, play a vital role in fish immune defense against pathogens. The administration of DnaK (bacterial homolog of HSP70) may be a strategy to potentiate the immune response and survival of aquatic organisms. This study evaluates the effect of cells overexpressing DnaK on mortality and immune-related gene expression in gnotobiotic sea bass larvae challenged with Vibrio anguillarum. Larvae were subjected to different treatments: NB (no bacteria), YS0 (E. coli with no plasmid), YS1 (E. coli expressing truncated DnaK), and YS2 (E. coli expressing DnaK), and then infected with V. anguillarum at 7 days post-hatching (dph). Mortality was monitored, and RT-qPCR was used to evaluate immune gene expression at 0, 18, 24, 36, and 120 hpc. While no significant variations were recorded in the non-challenged larvae, constant and sustained mortality was observed in challenged larvae from 60 to 120 hpc. However, lower mortality was observed in the larvae treated with DnaK. DnaK treatment promoted the expression of antimicrobial (hepcidin, transferrin) and chemotaxis genes (ccl4), which was further enhanced after a challenge with V. anguillarum, in conjunction with the modulation of il1β and il-8 at 120 hpc. These findings suggest that DnaK induces a potent innate immune response, improving survival against V. anguillarum and supporting its potential use as a disease-preventive strategy in aquaculture.

The skin of bony fish is the first physical barrier and is responsible for maintaining the integrity of the fish. Lesions make the skin vulnerable to potential infection by pathogens present in the aquatic environment. In this way, wound repair has barely been studied in gilthead sea bream. Thus, this study investigated the modulation of peripheral neuro-endocrine and tissue repair markers at the transcriptional level in the skin of teleost fish subjected to mechanical damage above or below the lateral line (dorsal and ventral lesions, respectively). Samples were evaluated using RT-qPCR at 2-, 4-, and 20-days post-injury. Fish with a ventral lesion presented a trend of progressive increase in the expressions of corticotropin-releasing hormone (crh), pro-opiomelanocortin-A (pomca), proenkephalin-B (penkb), cholecystokinin (cck), oxytocin (oxt), angiotensinogen (agt), and (less pronounced) somatostatin-1B (sst1b). By contrast, fish with a dorsal lesion registered no significant increase or biological trend for the genes evaluated at the different sampling times. Collectively, the results show a rapid and more robust response of neuro-endocrine and tissue repair markers in the injuries below than above the lateral line, which could be attributable to their proximity to vital organs.