Short-term effects of cortisol implantation on blood biochemistry and thyroid hormones in previtellogenic great sturgeon Huso huso

This study examined the effects of implanted cortisol on various aspects of intermediary metabolism of great sturgeon, Huso huso. Prior to experimentation all fish were examined using an endoscope to observe the stage of ovarian development. Subsequently, the 3-year-old female fish in the previtellogenic stage (mean body weight of 6759±53.2g) were intraperitoneally implanted with cocoa butter pellets containing cortisol to mimic the effects of chronic stress. The implant doses were 0 (C0; as control), 5 (C5) and 50 (C50) mg cortisol/kg body weight. Blood samples were taken every seven days during the four weeks of the experiment and analyzed for cortisol, glucose, adrenocorticotropic hormone (ACTH), total protein, total lipid, triiodothyronine (T3), thyroxine (T4), cholesterol and triglyceride content. Growth was reduced in all experimental groups and was not affected by cortisol treatment. Surprisingly, serum cortisol levels were higher in the C5 group than in the C50 throughout the experiment. A significant increase in glucose levels was observed in the cortisol-implanted fish from day 14 onwards. The high dose of cortisol elicited a significant increase in serum T3 and T4 levels. Fish implanted with the high cortisol dose also showed increases in serum ACTH, total lipid and cholesterol levels throughout a 28-day experimental period. The present study reveals that the negative effects of endoscopic surgery remain for at least four weeks and that a sustained-release implant of cortisol to mimic the effects of chronic stress affects metabolic responses. Since the adverse effects of endoscopic surgery on sturgeon welfare can be amplified by cortisol, special attention should be paid to the potential effects of chronic stress on sturgeon in culture.