Improving fish welfare in aquaculture has become a major concern in recent years. This is due to the inherent potential to maximize fish health and reduce the use of chemotherapeutics while minimizing the industry´s environmental impact and economic losses. Fish ability to cope with stress is a major health trait that can determine fish susceptibility to opportunistic pathogens and disease. The present work aimed to assess the effects of transport-induced acute stress on stress resilience as well as immune and oxidative stress responses of rainbow trout (Oncorhynchus mykiss) juveniles.
A trial with rainbow trout juveniles was devised to evaluate fish stress response after 2 h of transport. Fish were randomly distributed in triplicate groups of 40 fish (approx. 18 g) that were hand fed to satiation 2 times a day with a commercial-like diet. Following an acclimatization period, one group of fish was immediately sampled to serve as a non-stressed control. Additionally, two groups of fish were transferred, each, to 3 plastic containers (≈25 kg/m3) with an O2 saturated atmosphere and transported for 2 h. Upon arrival, one group of transported fish were immediately sampled while the remaining fish were accommodated in the original system and sampled 24 h post-arrival. Blood samples were collected for hematological procedures while plasma was used for cortisol, metabolites and humoral immune parameters. Liver was sampled for the analysis of metabolites and oxidative stress responses. Skin mucus and water were sampled both for proteomics and transcriptomics (miRNA) analyses, while skin tissue was collected solely for RNAseq analysis.
Results showed significantly increased plasma cortisol and glucose levels with a concomitant decrease of hepatic glycogen and glucose immediately after transport. Plasma immune parameters showed a significant increase of nitric oxide generation immediately after acute stress and higher hepatic lipid peroxidation and catalase activity in the recovery phase (24 h after transport). Regarding lipid metabolism, triglycerides increased in plasma whereas lactate decreased in liver 24 h after stress. Results suggested a stress induced response with clear primary and secondary stress response patterns characterised by increased plasma cortisol and the immediate mobilization of energetic resources from hepatic carbohydrate reserves, but also through the production of glucose using lactate as a non-hexose precursor in gluconeogenesis. Higher plasma triglyceride levels 24 h after stress might reveal an energy substrate shift from carbohydrates to lipids as a longer-term strategy by the organism to cope with stress.
Ongoing high throughput data analysis will allow a better understanding of stress and health biomarkers using minimally and non-invasive techniques.
Work Co-funded by UKRI and by the European Union’s Horizon Europe research and innovation programme (GA No. 101084651 - project IGNITION).