A Novel Method to Make Zebrafish Mate by Adding an Membrane Progestin Receptor Agonist to the Water Without Injection

This study investigates a novel method to induce mating in zebrafish (<i>Danio rerio</i>) by direct water addition of membrane progestin receptor (mPR) agonists, Org OD 02-0 (Org), or a maturation-inducing steroid, 17α,20β-dihydroxy-4-pregnen-3-one (DHP). Traditional spawning induction methods using hormone injections can be invasive and stressful for fish, especially small fish such as zebrafish. A previous study showed that progestins applied externally to the water can induce oocyte maturation and ovulation in female zebrafish. Then, a recent study showed that the addition of steroids and Org to the water also induced male sexual behavior in zebrafish. Therefore, it was hypothesized that the addition of these compounds to the water could induce mating in zebrafish. To address this, we investigated the efficacy of adding these compounds to the water in the vessel with a pair of zebrafish. Female and male zebrafish pairs were exposed to varying concentrations of DHP or Org in the water, and the resulting spawning rates and rate of sexual behavior induction were recorded. Our results showed that both simple addition of DHP and Org solution successfully induced mating within 4 h. A single chemical induced both spawning in females and sexual behavior in males. In this study, we have established a simple, novel method to induce mating in zebrafish by adding mPR agonists to the water.