Fertilisation of eggs, rate
of embryonic development and hatching following induced maturation of the
European eel Anguilla anguilla
B.
Hedegaard Pedersen-2004
Aquaculture, 237(1-4): 461-473
Abstract:
The study reports on 11 female Anguilla anguilla
in which sexual maturation was induced using modifications of a technique
that has proven successful in Anguilla japonica. In 10 of the
females, the outcome of fertilisation attempts is known. One female did not
respond to hormonal treatment and failed to break down the germinal vesicle;
in the remaining nine females, eggs were fertilised. In the eggs from two of
the females, embryonic development proceeded to the hatching stage, and in
one case, hatching occurred at about 48-h postfertilisation at an embryonic
stage when the tail had just passed the snout. Induction of maturation
consisted of weekly injections with salmon pituitary extract (SPE) at
18.2-mg pituitary powder per fish and week; the number of SPE injections
ranging from 11 to 29 before the oocytes had reached a stage when final
oocyte maturation and ovulation was induced by 1 mg of 17,20 ß-dihydroxy-4-pregnen-3-one
(DHP). At the time of DHP injection, the ooplasm and the oil droplets were
transparent and the nucleus was in the migratory stage near or at the animal
pole; cell diameters ranged from 763 to 930 µm. To avoid sudden
overripening of the eggs near the time of final oocyte maturation, the final
SPE doses were individually regulated—usually downregulated—relative to
the weekly dose, and this resulted in the use of four protocols for final
egg maturation. The best protocol, which resulted in hatching, used 13.6 mg
SPE followed 22 h 40 min later by DHP treatment when the oocytes had reached
the above stage. The second best protocol, in which the embryos developed to
the hatching stage, used a weekly SPE dose of 13.6 mg followed by a priming
SPE dose of 1.8 mg 2 days later, 11 h 40 min after which DHP was injected.
(Marine Biological Laboratory, University of
Copenhagen, Strandpromenaden 5, Helsingřr DK-3000, Denmark, e-mail: benedikte.pedersen@privat.dk)