# Efficacy of salmon GnRHa, Ovaprim® and hCG for hormonal stimulation of spermiation in the Fowler’s toad (Anaxyrus fowleri)

## TL;DR

This study compares hormones to stimulate sperm production in Fowler’s toads and finds hCG more effective than fish-derived hormones.

## Contribution

Demonstrates that fish hormones like salmon GnRHa and Ovaprim® are less effective than hCG for amphibian spermiation.

## Key findings

- hCG outperformed salmon GnRHa and Ovaprim® in sperm production and quality in Fowler’s toads.
- Ovaprim® caused higher sperm abnormalities and mass gain compared to hCG.
- Fish-derived hormone mixtures may not be suitable for amphibian breeding programs.

## Abstract

This study showed that hCG is better for stimulating sperm production, quantity and quality than two hormones commonly used in fish, including salmon GnRH and salmon GnRH + domperidone (Ovaprim). These results suggest that there may be limited transferability of fish hormones to amphibians within the bufonid Bufonidae family.

Ex situ amphibian populations can experience reproductive dysfunction due to the absence of environmental cues that trigger reproductive events. Assisted reproductive technologies (ART) for amphibians, specifically exogenous hormone regimens, can circumvent these external signals to induce gametogenesis and gamete release. Currently, the use of the mammalian reproductive hormones gonadotropin-releasing hormone (GnRH) and human chorionic gonadotropin (hCG) are used in a species-specific manner to stimulate amphibian breeding. Hormones or hormone mixtures that are effective in all breeding scenarios would provide the best option for conservation practitioners and some commercial products are already in use for breeding other ectotherms. Ovaprim®, which contains salmon GnRH analogue (sGnRHa) and the dopamine antagonist domperidone (DOM), is effective in fish aquaculture and may be effective for amphibians. To test this hypothesis, we treated Fowler’s toads (Anaxyrus fowleri) with either sGnRHa alone, a high or low dose of Ovaprim® or hCG. We then compared spermiation response, sperm quantity and quality parameters, and changes in animal mass over time within each treatment. We found administration of Ovaprim® resulted in more males producing sperm with better motility compared to administration of sGnRHa alone. In addition, the Ovaprim® and sGnRHa treatments resulted in lower response rates, lower sperm motilities, more abnormal sperm, and higher aggregations of sperm compared to the hCG treatment. Furthermore, Ovaprim®-treated males gained significant mass, suggesting an anti-diuretic effect of DOM. Together, these results show that neither Ovaprim® nor sGnRHa, at the concentrations tested, are likely suitable replacements for hCG in ex situ bufonid breeding programmes and that hormone mixtures developed for fish may have limited transferability to new world toad species.