Objective: This paper highlights the complexity of marine fish spawner–recruit systems and how they vary across species and ecosystems while providing a universal terminology and framework to evaluate fish reproduction. We emphasize the gonadal development important to assess maturity, fecundity, where and when fish spawn, and transition and sex assignment in protogynous species.Methods: We review and compare reproductive traits in warmwater and coldwater fishes. Reproductive phases for both sexes and protogynous species are defined and histological micrographs presented. New methods are developed to assess maturity; spawning seasonality; peak spawning; and, for protogynous species, sex assignment.Result: Protogyny, extended spawning seasons, and indeterminate fecundity are more common in warmwater than coldwater systems. The following reproductive phases are defined as immature, transitional (sex change), early developing (the first stage of entrainment in the reproductive cycle), late developing (stages needed to complete maturational competence), spawning, regressing (spawning season termination), and regenerating (fish that are mature but outside of the spawning season). A method to assess the certainty of maturity assignment based on reproductive phase and the age and size range sampled is presented, as are best practices to estimate size and age at maturity. To remove the subjectivity from current methods to estimate spawning seasonality, we present a new quantitative method to identify the core spawning season and peak spawning months.Conclusion: A species’ ability to adapt to fishing and climate change varies with their reproductive strategy. Improving our understanding of fish reproduction necessitates standardizing methodology and terminology.

Gag grouperMycteroperca microlepisare protogynous hermaphrodites, for which the assumption of female-driven reproductive potential may be inaccurate. In protogynous species, male abundance, fertilization success, and stock productivity are affected by where and when sex change occurs and how fishing pressure affects male recruitment and survivorship. In this study, we integrated large spatial-scale data with high-resolution data from a 3 yr study sampling gag at deep-water sites with varying spatial management (a marine protected area [MPA], a seasonally closed area, and an 'Open area'). Gag exhibited complex spatial ecology; females formed pre-spawning aggregations before migrating to deep-water spawning sites, which overlapped with locations where males were sampled year-round. The observed male sex ratio in the MPA was 5% compared to the expected 15%. It was 0% in less protected areas. Sex change occurred occasionally in small fish and before, during, and after the spawning season. In addition, sex change was observed in pre-spawning female-only aggregations as well on the spawning grounds, indicating that male social cues are not requisite. We propose that shallow-water, pre-spawning aggregations are a key spatio-temporal bottleneck to gag productivity. They appear to be an important source of transitionals and are heavily fished, which may negatively impact male recruitment to the spawning grounds. Our results indicate that overall gag abundance is low, MPAs do not protect all recruiting males (as previously assumed), and current regulations are not sufficient for the male population to recover to historic levels (~17% male).