The eel life cycle is complex with an oceanic and a continental phase.During silvering, a process marking the onset of spawning migration, the gonadal development is inhibited by complex hormonal control mechanisms. This inhibition must be released once the eels reach their spawning areas, but these mechanisms remain unrevealed.
The emerging yolk-sac larvae develop over a 12-day period into the feeding stage, i.e. the leptocephalus stage, however, little is known about their prey and feeding behavior. These transparent leaf-shaped larvae drift with the currents over months to reach the continental shelf, upon which they transform into glass eels.
Reproducing eels in captivity therefore meets particular challenges that need to be addressed such as induced maturation, viable gamete and offspring production, larval culture conditions and feeding. This adds further complexity to common problems encountered in aquaculture, e.g. enhanced broodstock feed for optimal gamete quality, optimization of fertilization procedures, establishment of first feeding, and larval ongrowing.
The life cycle of eel. Modified from W. Dekker.
In the EEL-HATCH project, modern technology, constructing controlled aqua-systems for broodstock husbandry and large-scale production of offspring, will be applied to enhance efficiency in production and exploit the reproductive potential of single broodstock females and males.
European eel females are highly fecund, producing up to 500,000 eggs in one batch. Optimized utilization of this reproductive capacity might enable cost-efficient production methods. These methods comprise broodstock conditioning, farmed broodstock dietary management prior to the non-feeding maturation stage, assisted reproduction, and larval culture throughout the leptocephalus stage.