Effect of oxygen saturation in water on reproductive performances of Pacu Piaractus brachypomus

Broodstock pacu Piaractus brachypomus as well as their eggs during their embryonic development were exposed to either normoxia (5.5-7.5 mg O₂/L) or hypoxia (2.0-4.5 mg O₂/L) conditions. The plasma concentrations of 11-ketotestosterone in males and estradiol-17β in females, as well as that of their precursor testosterone (T) were significantly (P < 0.01) higher in fish maintained under normoxic conditions than in fish exposed to hypoxia. After ovulation and spermiation induced by hormonal treatments, the plasma concentrations of T and 17,20β-dihydroxy-4-pregnen-3-one (17,20βP) significantly (P < 0.05) increased in both sexes under both normoxic and hypoxic conditions. The plasma levels of T and 17,20βP achieved under normoxic conditions were higher than the ones recorded under hypoxia, except for those of 17,20βP in males. Males responded positively to the hormonal treatments, and the concentration of spermatozoa was 10.5 ± 0.8 10⁹/mL under both oxygen conditions. Hypoxia resulted in significantly lower survival of embryos (17.3 ± 28%) in comparison to normoxic conditions (68.5 ± 25%). Moreover, larval deformities were found when exposed to hypoxia (91.6 ± 6%). During embryonic development of this species 4 mg/L of oxygen is tolerated at 26-27 C without negative impact. We conclude that despite the highly adaptable nature of adult pacu to environmental hypoxia, oxygen concentrations below 4 mg/L severely impacted survival of embryos.