The ratio of length at first maturity to maximum length across marine and freshwater fishes

Abstract

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. In this study, the authors assess if this critical ratio is consistent across 132 unique fish species, as measured by the slope of the relationship between LmaxD and LmD, 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 LmaxD/LmD ratio equivalent to the Qm/Qmaint ratio. The authors found that across all species, the LmaxD/LmD ratio was 1.40 (95% c.i. 1.38–1.42), which was not significantly different from that previously estimated across other species groups (1.35, 95% c.i. 1.22–1.53), especially when phylogenetic relationships were considered (1.25, 95% Bayesian credible interval 1.09–1.40). The consistency of the LmaxD/LmD 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.

A reconceptualization of the interactions between spawning and growth in bony fish

“…In the following, we present a reconceptualization of spawning based on Pauly (2019Pauly ( , 2021aPauly ( , 2019b) and evidence presented on Chen et al (2022) and other authors. However, before this can be presented, a brief review of fish growth and related matters is necessary.…”

Why do fish reach first maturity when they do?

“…= 1.17–1.42). Nonetheless, the corrected estimate remains statistically indistinguishable from the estimate of 1.35 by Meyer and Schill (2020), who studied 51 populations in three salmonid species (Figure 4b), from 1.30 (1.17–1.43) in 51 species of freshwater and marine fishes in and around Turkey (Figure 4c; C. Keskin & D. Pauly, unpublished data), from 1.41 (1.37–1.44) in 96 species of Chinese freshwater and marine fishes (Figure 4a; Chen et al ., in press) and from 1.35 (1.18–1.53) in the females of 41 natural or feral populations of 7 species of Cichlidae, including 4 tilapia species in Amarasinghe and Pauly (2021).…”

“…; (c) C. Keskin and D. Pauly (unpublished data) on freshwater and marine fishes in and around Turkey, including accounting for phylogeny; (d) Chen et al . (in press) on freshwater and marine fishes of China, including accounting for phylogeny; note that when phylogeny is considered [as in (d)], the regression lines are shifted to the right and seem not to fit the data; (e) finally pertains to the females of 41 populations in 7 species of cichlids (Amarasinghe & Pauly, 2021)…”

The impact of the human activities on aquatic ecosystems

“…(2022) and Chen et al . (2022) both highlight the need for challenging concepts or knowledge that might need to be readdressed and investigated using up‐to‐date approaches. Pauly (2022) asked in his keynote a long‐standing question in the field of fish physiology: “Why do fish mature when they do?” and challenges the idea that environmental controls are the main drivers of such important parameters.…”

“…Following from this, Chen et al . (2022) analyses a large data set and suggests maturation might be instead linked to the relationship between oxygen supply and the oxygen demand of fish.…”