Duration of migration and reproduction in males is dependent on energy reserve in a fish forming spawning aggregations

Abstract

Clarifying the relationship between individual energetic state and reproductive behav- iour is essential for understanding the life history strategies of fish as well as for determining fisheries management measures. Many papers have recently been published on fish spawning aggregations (FSAs), in which numerous fish migrate to specific sites for spawning, yet little is known about the relationship between individual energetic state and reproductive behaviour. We tested whether the individual energetic state affected the reproductive behaviour in male white-streaked grouper Epi- nephelus ongus, a species that forms FSAs. Body composition measurement of market specimens suggests that male E. ongus feed less and mainly use their lipid reserves for metabolism and testis development during the spawning season. An integrative analysis of body composition and acoustic telemetry data showed that there is a positive relationship between pre-migration lipid density and duration away from the resident area for migration and reproduction (duration away). These results indicate that fatter males with higher lipid density spent longer periods outside of the resident area, which may enhance the susceptibility of these individuals to intensive fishing pressure at the FSA site. Furthermore, the lipid expenditure during the duration away estimated in this study corre- sponded well with the energy expenditure for metabolism and testis development estimated through the metabolic theory of ecology, suggesting that we could accurately estimate the energy requirement for reproductive behaviours. This study highlights the importance of linking energy reserves to reproductive behaviours in other fishes forming spawning aggregations.