Effect of enrichment on gamete production, gamete quality, and spawning coloration in hormonally induced redside dace Clinostomus elongatus

Due to the alarming rates of freshwater fish extinctions, urgent action is needed to develop captive breeding programs for imperiled species and enhance existing practices to improve reproductive outcomes. Here, we investigated the effects of enrichment on gamete production, quality, and spawning coloration following hormone injection (i.e. carp pituitary, gonadotropin) in the endangered redside dace Clinostomus elongatus , a sexually dimorphic, presumably obligate nest parasite. C. elongatus were reared in either a non-enriched environment (i.e. barren) or an enriched environment (i.e. substrate, plants, and spawning nest-building hosts) for 1 yr prior to hormone induction. We found no differences in the proportion of free-flowing gamete expression between male and female C. elongatus in the non-enriched and enriched environments. However, males reared in enriched environments had higher sperm motility, while among females, there was no significant difference in egg diameter. Furthermore, enrichment was found to influence spawning coloration, with males and females reared in enriched environments displaying redder hues compared to those reared in non-enriched environments prior to hormone induction. However, post hormone injection, no significant differences in red coloration were observed between non-enriched and enriched males and females, indicating that hormone induction improved coloration in non-enriched fish. This study highlights the effect of enrichment on gamete production, quality, and spawning coloration and provides information for captive breeding C. elongatus . These findings provide valuable insights into the potential of enrichment and induction techniques to enhance reproductive outcomes when captively breeding endangered species of fishes.