Cortisol responsiveness to stress in channel catfish influences susceptibility to Edwardsiella ictaluri

Authors: Chatakondi, Nagaraj; Peterson, Brian

Submitted to: Southeastern Association of Fish and Wildlife Agencies Conference
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/20/2017
Publication Date: 3/14/2018
Citation: Chatakondi, N.G., Peterson, B.C. 2018. Cortisol responsiveness to stress in channel catfish influences susceptibility to Edwardsiella ictaluri. Southeastern Association of Fish and Wildlife Agencies Conference. 5:53-58.

Interpretive Summary: Disease is considered the single most cause of reduction production in aquaculture. Mortality rates increase with cortisol concentrations when healthy channel catfish are stressed before becoming infected with disease. Low and high cortisol responding to standardized stress were identified in a select strain of channel catfish and subject to Edwardsiella ictaluri disease challenge under controlled conditions. Effect of rearing conditions (mono-culture or co-culture) of low and high cortisol responders to disease susceptibility did not differ. Mortality rates of channel catfish increased with an increase in cortisol responsiveness to stress in channel catfish. Our findings suggest that one episode of low dissolved oxygen stress exposure differentiated low and high responders of channel catfish to standardized stress. ESC is a disease capable of producing mortalities very quickly. Low responding channel catfish had a lower cumulative mortality (38%) compared to higher responding channel catfish (59%) to ESC disease under controlled conditions.

Technical Abstract: Stress is unavoidable in aquaculture and hence strains of fish that are resilient and adaptable to stress need to be developed. Past studies have demonstrated that fish subjected to handling stress or poor water quality had reduced ability to resist pathogens. Cortisol is the primary stress hormone in teleosts and its plasma concentration typically correlates with stress response. The objective of the study was to assess if cortisol responsiveness to stress in channel catfish, Ictalurus punctatus influences susceptibility to Edwardsiella ictaluri under controlled conditions. In the first experiment, six month old channel catfish fingerlings were subjected to standardized hypoxia stress (1.8 ppm of dissolved oxygen for 5 min) to classify them as either ‘low responders (LR)’ or ‘high responders (HR)’ based on their plasma cortisol concentration. In the second experiment, HR and LR fish were held either in individual or co-cultured in 80 L aquaria and were challenged with virulent E. ictaluri (1.9 x 107 cfu/mL) by an in situ bath immersion to evaluate their susceptibility to the pathogen. At the end of the 21 day challenge, mean percent mortality of LR fish (38.1+ 2.1) was lower (P<0.05) than the mean percent mortality of the HR group (59.0 + 1.8). An increase in susceptibility of HR fish to E. ictaluri may be the result of their higher responsiveness to standardized stress. Hence, the results of the present study suggest LR fish may be resilient and adaptable to stressful conditions.