The impact of net cleaning on fecal cortisol metabolites in farmed Atlantic Salmon

Abstract

Stress assessment is crucial in aquaculture to ensure and improve the health and well-being of production animals including fish. The primary objective of this study was to utilize the assessment of fecal cortisol metabolites (FCMs) as a low-invasive stress determination method for farmed Atlantic salmon (Salmo salar L.) and to suggest an appropriate sampling timeframe for this measurement.Blood, mid-intestinal contents, and feces samples were collected before, during, and at 2 and 20 h after a stress-inducing event, namely, net cleaning. Plasma cortisol (PC) and its metabolite levels in the mid-intestinal contents (MICMs) and FCMs were assessed by an enzyme-linked immunosorbent assay (ELISA). The research reveals a distinctive temporal profile, with a sequential elevation in levels of PC, MICMs and FCMs in response to the effects of net cleaning. Peak FCMs levels were observed approximately 20 h after net cleaning and were significantly higher than peak PC levels (P < 0.05). The findings suggest that FCMs are a promising indicator for acute stress assessment. To enhance the understanding and improve the applicability of FCMs as stress indicators in fish farming practices the critical challenges regarding feces sampling and FCMs analyses are further discussed. Future research aimed at developing practical protocols and industry standards will emphasize method validation and include a greater number of sampling points as well as an expanded experimental period.This study signifies a crucial step toward understanding the role of FCMs as a reliable stress indicator in fish. It underscores the importance of accounting for the delayed and extended sampling patterns when assessing stress in aquatic settings. Moreover, it offers a less invasive and more labor-efficient approach for monitoring the overall health and welfare of salmonids than PC analysis, thereby promoting sustainability in this vital industry.