ml kg-1 and 2.6 ml kg-1, respectively. The priming dose (50% and 10% in males and females, respectively) was administered in the morning, whereas the resolving dose (50% and 90% in males and females, respectively) was injected at 20:00 h.
Blood was collected from the caudal vessel of unanaesthetized fish prior to the priming injection and two days after the injections using heparinized syringe. Blood samples were centrifuged at 1,500 g for 5 min and the resulting plasma was stored at Ð20¡C until assays. The plasma concentrations of steroids (testosterone, estradiol-17 , 11-ketotestosterone and 17,20 -dihydroxy-4-pregnen-3-one) were measured by radioimmunoassay similar to those used previously (Ottobre et al., 1989) following ethyl-ether extraction. [1,2,6,7-3H]testosterone (96.5 Ci/mmol) and [2,4,6,7,16,17-3H]estradiol (141 Ci/mmol) were purchased from NEN Life Science Products (Boston, MA, USA). [3H]11-ketotes
Table 1. Radioimmunoassay characteristics of steroid hormones in Colossoma macropomum. T = testosterone, E2 = estradiol-17 , 11-kT = 11-ketotestosterone, and 17,20 P = 17,20 -dihydroxy-4-pregnen-3-one
Table 2. Plasma sex steroid hormones of male and female Colossoma macropomum before and after hormonal treatments. T = testosterone, E2 = estradiol-17 , 11-kT = 11-ketotestosterone, 17,20 P = 17,20 -dihydroxy-4-pregnen-3-one, and nd = not detected. For each sex, means within the same column with different letters are significantly different (P < 0.01).
Table 3. Concentrations of Plasma sex steroid hormones of Colossoma macropomum collected on 16 April 2002. T = testosterone, E2 = estradiol-17 , 11-kT = 11-ketotestosterone, 17,20 P = 17,20 -dihydroxy-4-pregnen-3-one, and nd = not detected.
