Background
Glasaal Volendam is a private research company which aims to close the life cycle of European eel Anguilla anguilla in captivity. The lengthy life cycle of European eel begins with hatching in the Sargasso Sea . From there larvae drift as leptocephali back to the coasts of Europe, transforming into glass eels. After entering rivers and migrating upstream , once sexually mature they migrate back to the Sargasso Sea to complete the life cycle. Glasaal Volendam made considerable progress in recent years towards closing the life cycle of European eel in captivity, producing high-quality gametes and embryos.
Materials and methods
During the maturation period in RAS , wild female eels are kept at low density (20 kg/m3), with 36‰ salinity and 18° C. To induce vitellogenesis, females receive weekly injections of Carp Pituitary Extract (CPE) (Kagawa et al., 2005) . To induce ovulation, females are injected with DHP (7α,20ß-dihydroxy4-pregnen-3-one ) according to Ohta et al. (1996) . Male broodstock is obtained from commercial eel farms and receives weekly injections of human chorionic gonadotropin (Perez et al. 2005). Fertilized eggs are incubated for 48 hours before hatching. On day 14 after hatching , larvae are moved to feeding tanks for experiments .
Results and future steps
Currently Glasaal Volendam can produce large numbers of fertilized eggs weekly . Survival rates at the start of the feeding were improved from 0.3% in 2018 to 15% in 2023 . In 2022, for the first time, a batch of larvae showed growth . In 2023 larvae reached the 2 cm in length and more than 230 days of age. In 2024 the research is focusing on testing different diets and environmental parameters to evaluate their effects on survival and growth of pre-leptocephalus and leptocephalus larvae. This presentation aims to give an overview of the rearing of eel leptocephalus larvae.
References
Kagawa, H., Tanaka, H., Ohta, H., Unuma, T., Nomura, K., 2005. The first success of glass eel production in the world: basic biology on fish reproduction advances new applied technology in aquaculture. Fish Physiol. Biochem. 31, 193.
Ohta, H., Kagawa, H., Tanaka, H., Okuzawa, K., & Hirose, K. (1996). Changes in fertilization and hatching rates with time after ovulation induced by 17, 20P101 dihydroxy-4-pregnen-3-one in the Japanese eel, Anguilla japonica. Aquaculture, 291–301.
Pérez L, Asturiano J.F., Tomás A. , Zegrari S., Barrera R. , Espinós F.J., Navarro J.C. , Jover (2000) Induction of maturation and spermiation in the male European eel: assessment of sperm quality throughout treatment. J. Fish. Biol. 57(6):1488–1504.
Sørensen S.R., Tomkiewicz J., Munk P., Butts I.A., Nielsen A., Lauesen P., Graver C. (2016b) Ontogeny and growth of early life stages of captive-bred European eel. Aquaculture 456:50–61.