Authors : Todd D. Sink , Richard J. Strange , Hugo Eiler and Kellie Fecteau
Abstract: Diagnostic tests using hormones in fisheries sciences are lacking when compared to other animal production industries. The goals of this study were to:1) examine how manipulation of the hypothalamic-pituitary-interrenal axis using dexamethasone (Dex) and adrenocorticotropic hormone (ACTH) changes disease susceptibility of channel catfish to ESC, 2) evaluate Dex as a possible way to reduce the negative effects of stress during confinement and transport and 3) determine the effects of the synthetic hormones dexamethasone and Cortrosyn® (ACTH) on blood plasma cortisol concentrations of stressed and unstressed channel catfish fingerlings in addition to evaluation of the effects Dex and ACTH have on blood plasma mineral concentrations in channel catfish. A series of disease challenges using Edwardsiella ictaluri in combination with hormonal treatments were used to assess these goals. Manipulation of the hypothalamo-pituitary-interrenal axis using Dex and ACTH does change disease susceptibility of channel catfish. Cortisol concentrations were assumed to be correlated with mortality in fish and mortalities for control treatments were low as expected. Other treatments demonstrated a lack of differentiation in mortalities and could not be explained by cortisol. Dex treatments exhibited low cortisol (7.4�1.2 ng mL 1) concentrations and had the greatest mortality (78.3%�11.7). Dex was not different from ACTH (66.7%�6.0) and ACTH stress 30 min (51.7%�1.7) which were expected to exhibit the greatest mortality. Mineral analysis revealed that there were no differences in blood plasma concentrations of sodium, potassium and chloride in any treatment. Dex was effective at suppressing the stress hormone cortisol in both stressed (17.5�2.3 ng mL 1) and unstressed (7.4�1.2 ng mL 1) catfish. Although Dex is capable of suppressing ACTH and cortisol, its use as a stress preventative, especially for the reduction of disease susceptibility is unfounded based on this study due to increased mortality rates associated with its use (78.3%�11.7).
Todd D. Sink , Richard J. Strange , Hugo Eiler and Kellie Fecteau , 2006. Changes in Susceptibility of Channel Catfish, Ictalurus punctatus, to Enteric Septicemia of Catfish by Hormonal Altering of the Hypothalamo-Pituitary- Interrenal Axis. Journal of Animal and Veterinary Advances, 5: 200-207.