Effect of ambient oxygen on growth and reproduction in Nile tilapia (Oreochromis niloticus)

Growth, size at maturity, gonadosomatic index (GSI), egg size, and absolute fecundity of Nile tilapia ( Oreochromis niloticus ) were significantly affected by oxygen levels (1.5 ± 1.0, 2.8 ± 1.4, and 6.0 ± 1.8 mg·L –1 ) in a controlled experiment designed to test the hypothesis (D. Pauly. 1984. J. Cons. Int. Explor. Mer, 41: 280–284) that O 2 is the controlling factor for the transition from juvenile to adult in fish, in general, in the context of phenotypic life history plasticity and “stunting” in tilapias. Size at maturity and the estimated asymptotic size decreased with decreasing O 2 concentration, as predicted by Pauly’s hypothesis. All fish matured at the same age (18 weeks old), which is in contrast to conventional definitions of stunting. This finding challenges the suggested plasticity in age at first maturity for tilapia. The results also challenge the hypothesis that stunting is a unique recruitment mechanism, as the smaller fish in the group with low oxygen concentration produced smaller and fewer eggs than the larger fish in the group with high oxygen concentration.