The effects of gonadotropin-releasing hormone analog on yellowtail kingfish Seriola lalandi (Valenciennes, 1833) spawning and egg quality

• We examined the usefulness of GnRHa implant in yellowtail kingfish (Seriola lalandi) to increase the number of contributing parents.
• Genotyping showed that GnRHa implant increased number of females contributing eggs.
• However, GnRHa implant was associated with reductions in egg quality, likely related to suboptimal timing of implantation.

Communal spawning behaviour in marine aquaculture species often results in a few individuals contributing disproportionate amounts of gametes. This can lead to a reduction in genetic variability and increases the risk of inbreeding among successive generations. Therefore, long term sustainability of captive breeding programmes for such species partly depends upon maintaining a sufficiently high proportion of parents contributing high quality gametes during spawning. The current study was conducted to evaluate if the use of slow-release gonadotropin-releasing hormone analog (GnRHa) implants could increase the number of females spawning high quality gametes, and thus increase genetic variation in a captive population of yellowtail kingfish Seriola lalandi (Valenciennes, 1833). Broodstock fish received implants with or without 500 μg of GnRHa during the spawning season. GnRHa treatment was associated with a higher proportion of females contributing to spawning. However, compared to eggs from non-GnRHa-treated broodstock, GnRHa significantly decreased the floating rate, fertilisation rate, number of viable eggs and egg oil globule diameter. Overall, the use of slow-release GnRHa implants is a useful tool to increase parental contribution to spawning, but this benefit must be carefully balanced against lower egg quality.