Response of sex ratio to timing of breeding in the small cyprinid Gnathopogon caerulescens

Abstract

The influence of hatching date on the sex ratio of wild Gnathopogon caerulescens was examined. Cohorts reared from eggs collected in the early and middle parts of the spawning season showed almost balanced sex ratios, with female bias in some cohorts. Cohorts born later in the season mostly displayed male bias, and the mean proportion of males later in the season was significantly higher than in early- and mid-season cohorts. These results indicate that the sex ratio of G. caerulescens changes with the time of breeding, increasing along with the ambient water temperature of the lake.

Podocnemis expansa Turtles Hint to a Unifying Explanation for the Evolution of Temperature-Dependent Sex Determination in Long-Lived and Short-Lived Vertebrates

“…This hypothesis has been demonstrated by elegant studies in a few short-lived vertebrates: the silverside fish Menidia menidia [Conover, 1984;Duffy et al, 2015] and M. peninsulae [Yamahira and Conover, 2003], and in Amphibolurus muricatus lizards [Warner and Shine, 2008]. Some data suggest that the same may be true in Gnathopogon caerulescens [Fujioka et al, 2015] and Micrometrus minimus [Schultz, 2008] fish and in Agama picticauda [Steele and Warner, 2020] and other short-lived lizards [Warner et al, 2009]. The short life span of these species makes this adaptive scenario plausible, while the protracted growing season of long-lived taxa such as turtles would preclude its applicability in this exact manner.…”

Daily growth increments in otoliths of wild‐caught honmoroko Gnathopogon caerulescens

“…They inhabit shallow estuaries during the larval and juvenile stages, moving to the pelagic zone as adults, determined from the recapture of alizarin complex one (ALC)‐marked fish (Kikko et al, ). Individuals migrate from the main lake to the lagoon and shoreline habitats for spawning, from April to July (Fujioka et al, ; Kikko et al, ; Kikko, Ishizaki, et al, ; Kikko, Usuki, et al, ). Many ALC‐marked fish, released to the lagoons, were subsequently recaptured offshore in the main lake during autumn and winter, suggesting that recruitment contributions from the lagoons to the main lake were substantial (although fluctuating yearly; unpubl.…”

Juvenile migration of the exclusively pelagic cyprinid, Gnathopogon caerulescens (Honmoroko) in Lake Biwa, Central Japan

“…Honmoroko Gnathopogon caerulescens (Sauvage 1883), a small cyprinid (total length, L T ≤ 14 cm) endemic to Lake Biwa, has an exclusively pelagic life cycle in the northern basin, foraging for zooplankton (Nakamura, , ). The fish spawns in lagoons adjacent to the northern basin and in shoreline habitats from April to July (Fujioka et al, ). The former are particularly suitable as nursery grounds, being highly productive and providing refuges from predation (Shibata et al, ; Kikko et al, ).…”