Using Osmotic Pumps to Induce the Production of Gametes in Male and Female European Eels

SIMPLE SUMMARY: The European eel is a species with high commercial value for aquaculture, and it has suffered a drastic reduction of its natural stocks during the last decades; thus, breeding in captivity is nowadays considered essential to avoid the extinction of the species. In this sense, a new method to maturate the European eel (males and females) for eel aquaculture has been studied. For the first time in the European eel, a controlled release hormone system (osmotic pumps) has been tested, which allowed to induce the testis maturation and sperm production in part of the males as well as a very early maturation and ovulation in the females. ABSTRACT: The European eel (Anguilla anguilla) is a commercially valued species for aquaculture. Over the past decades, it has experienced a drastic reduction in its natural stocks. Thus, breeding in captivity is considered essential, nowadays, to guarantee the eel aquaculture and to reduce pressure on natural populations. Traditionally, the European eel has been sexually matured by means of weekly hormonal injections, which cause stress to the fish. The purpose of this research study was to assess the use of osmotic pumps as a new method to induce sexual maturation in male and female European eels, without the weekly injection. The control groups were treated with weekly hormone injections (recombinant human chorionic gonadotropin for males and carp pituitary extract for females), and the implanted groups were treated with osmotic pumps (ALZET(®) osmotic pumps) loaded with the respective hormones. Regarding male European eels, this study shows that the use of controlled release systems was able to induce the maturation and spermiation, but without the necessary capacity to produce enough gametes with acceptable quality parameters that could meet the needs of a commercial eel hatchery. Concerning female European eels, the study demonstrates that the use of osmotic pumps loaded with CPE became an effective method, generating early maturations (4 to 10 weeks) in 50% of the females, so this method could become a viable alternative for eel hatchery procedures.