LAUSR

The prevailing determinant of maturation in fishes is thought to be a redirection of energy from growth to reproduction. Instead, the Gill Oxygen Limitation Theory predicts that maturation, and thus reproduction, is induced when a fish reaches a critical ratio of oxygen supply to demand (Qm /Qmaint ). The consistency of this critical ratio has been previously documented in many fishes, but a broader test was lacking. Here, we assess if this critical ratio is consistent across 132 unique fish species, as measured by the slope of the relationship between Lmax D and Lm D , where Lmax is the maximum length reached in a given population, Lm is the mean size at first maturity in that population, and D is a gill-related exponent which renders the Lmax D /Lm D ratio equivalent to the Qm /Qmaint ratio. We found that across all species, the Lmax D /Lm D ratio was 1.40 (95% Confidence Interval [CI] 1.38-1.42), which was not significantly different from that previously estimated across other species groups (1.35, 95% CI 1.22-1.53), especially when phylogenetic relationships were considered (1.25, 95% Bayesian Credible Interval 1.09-1.40). The consistency of the Lmax D /Lm D ratio across taxa, which expresses the difference in metabolic rate at maturity and maximum size, suggests that the scaling of gill surface area is the factor that underlies this ratio, and which triggers the maturation in fishes. This article is protected by copyright. All rights reserved.