Retardation of ovarian growth and depression of serum steroid levels in the tilapia, Oreochromis mossambicus, by cortisol implantation

Abstract

Female Oreochromis mossambicus were implanted with cortisol suspended in cocoa-butter for the evaluation of the chronic effects of cortisol on reproduction. Implant doses of 1.5 and 3.0 mg/g body weight, mimicking the effects of long-term chronic stress, suppressed various reproductive parameters over the 18-day treatment period. Most fish treated with cortisol showed reductions in body weight. Oocyte size and gonadosomatic index of treated fish became significantly lower than the control after 9 and 12 days of treatment, respectively. The retardation of oocyte growth was accompanied by depression of serum testosterone and oestradiol-17β levels. © 1993.