New Zealand’s iconic whitebait fishery (mostly Galaxias maculatus, or īnanga) is unique, and its complexities for management are numerous. As a precautionary conservation measure, several areas on the West Coast were closed to fishing to prevent overexploitation. Some of these whitebait reserves involve areas completely protected from the whitebait fishery (closed), whereas others protect tributaries but allow fishing downstream (partially closed). After populations recover from fishing pressure, abundances and densities of formerly-fished species usually increase, and we should therefore expect changes in life-history traits compared to those in exploited populations. To test this, we examined the additive and interactive effects of individual size, population density, and stream temperature on īnanga growth rates and fecundity across a density gradient mediated by levels of fishery closure (closed, partially closed, and no protection). Specifically, increased abundance but reduced growth rates were found in high-density (closed) sites. However, there was no evidence of a trade-off between egg size and fecundity, or of negative density-dependent effects on fecundity or egg size within the whitebait reserves. Īnanga fecundity increased with body size, highlighting the importance of available forage (terrestrial- and stream-based prey) to maintain individual growth in dense populations. This study emphasises the importance of understanding how the life-history traits of exploited populations respond to fishery closure. For the whitebait reserves to be more effective as a management tool, efforts should focus on the remediation of in-stream and requisite riparian spawning habitats, the degradation of which has caused population bottlenecks for this culturally and economically important amphidromous species. The major subsidy from whitebait reserves for īnanga is sustainable egg production if migration to sea of the greatest possible number of larvae can be ensured.