Assessment of osmotic pumps as a method to induce sexual maturation of European eel males and females

The sexual maturation of the European eel (A. anguilla) has been traditionally induced by hormonal treatments, requiring weekly handling and causing fish stress. The osmotic pumps (OP) were tested as an alternative method for induction of maturation of eel males and females. Males were divided in Control, OP-100 and OP-200 groups (n=10/group). The control group received weekly injections of recombinant hCG (1.5 IU/g fish) for 15 weeks. The induction of sexual maturation of OP groups was carried out by implanted hCGrec-loaded osmotic pumps (ALZET 1004 and 2006). Sperm samples were weekly collected by stripping and several sperm parameters were evaluated by CASA. Biometric parameters such as fin color and gonadosomatic index were evaluated as key indicators of maturation. Blood samples were taken and 11-ketotestosterone levels determined by a specific EIA. Osmotic pumps induced the maturation and spermiation in males, but without the required intensity to produce a sufficient quantity of gametes (sperm volume, density) or quality parameters (motility) for aquaculture purposes. Eel females were divided in Control (n=11) and OP-2ML4 group (n=10). The control group received weekly injections carp pituitary extract (CPE; 20 mg/kg fish) for 15-20 weeks. The OP2ML4 group was implanted with a CPE-loaded OP ALZET 2ML4. The females were weekly monitored and those riped were induced to spawn and artificial fertilization was performed. The gonadosomatic index was also evaluated. The results showed that OP evoked an unusual early maturation in some females, evidencing that this method might become a viable alternative for eel hatchery procedures.