Abstract
Simple SummaryThe 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.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.
Highlights
The European eel (Anguilla anguilla) is a commercially valued species, especially for the Japanese and European markets
In order to overcome the lack of natural spawning stimuli in captivity, the sexual maturation of both males and females must be induced with long-term hormonal treatments [4,5,6]
The traditional hormonal treatments to induce sexual maturation in fish entails a continuous handling of the animals, which has a negative impact on the maturation process due to the stress suffered by the fish
Summary
The European eel (Anguilla anguilla) is a commercially valued species, especially for the Japanese and European markets. Over the past 50 years, populations of the European eel have been declining, and the recruitment of glass eels has collapsed since the early 1960s [1]. Overfishing, habitat reduction, pollution, and the swimbladder parasite (Anguillicola crassus) are some of the causes that have led to the decline of the European eel [2]. As a result, it was included in the Red List of the International Union for Conservation of Nature (IUCN) as a “Critically. Nowadays, controlling the reproduction and ability to produce glass eels seems to be the only sustainable solution to reduce the pressure on natural populations. In order to overcome the lack of natural spawning stimuli in captivity, the sexual maturation of both males and females must be induced with long-term hormonal treatments [4,5,6]
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