| Abstract: | The tambaqui Colossoma macropomum is the most important native fish in Brazilian aquaculture. Females are almost 20% heavier than males and therefore are more profitable. Based on this information, we tested four different concentrations (20, 40, 80, and 120 mg/kg diet) of oestradiol (E2) offered during 6 weeks to tambaqui larvae and analysed their efficiency in producing female monosex batches of the species. The study was performed in two independent tests, using different genetic backgrounds (broodstocks). All treatments increased the percentage of females in the population, but only the highest E2 dose was “free” of males in both tests. All treated groups contained intersex individuals (when sex inversion is not complete). Plasmatic E2 concentration was similar between treated and non‐treated fish 60 days after the treatment in fish treated with 20, 40, and 80 mg E2/kg diet. However, tambaqui treated with a 120 mg E2/kg diet showed lower E2 plasma concentration in comparison with the control group. Last, we chlorinated the water to ensure the environmental integrity of the study. Three days after chlorination, the water was completely free of any oestradiol residue (analysed by high‐performance liquid chromatography). |
