Hormonal status and phagocytic activity in sea bream infected with vibriosis

Abstract

Serum taken from female, sexually mature, silver sea bream (Sparus sarba) displaying either no symptoms of vibriosis, mild infection, severe infection or moribundity were assayed for a number of key hormones. Serum cortisol levels were not significantly different among symptomless, mildly- and severely-infected groups, whereas moribund fish displayed hypercortisolemia with a 14-fold increase in serum cortisol in comparison to symptomless fish. Serum estradiol levels were significantly reduced 19-fold in mildly-infected fish and remained at a low level as infection progressed, whereas serum testosterone increased gradually during vibriosis with a 1.8-fold increase in moribund groups in comparison to symptomless groups. Both serum thyroxine (T4) and triiodothyronine (T3) gradually decreased during vibriosis being 26- and 2.8-fold lower, respectively, in moribund fish in comparison to symptomless fish. The non-specific immune response, as determined by phagocytic activity, was also assessed using macrophages isolated from the pronephros and spleen of infected fish. Phagocytic indices significantly increased in mildly- and severely-infected fish and then decreased from these stimulated levels in moribund fish.