chapter 3 - RiuNet

GENERAL DISCUSSION
1. Improvements to the control of European eel reproduction
The control of the reproduction of the European eel has become the focus
of much research due to the severe decline in the natural stocks.
Nowadays breeding in captivity seems to be the only alternative both in
order to reduce the pressure on natural populations and to meet the
demands of the eel farms (Feunteun, 2002).
In a breeding captivity program, the first step is to achieve high quality
gametes in order to reach high fertilization and hatching rates (Bozkurt et
al., 2006). During this thesis, alternative treatments for the induction of
maturation were carried out with the aim of improving several male
reproductive traits in the European eel such as the onset and the duration
of the spermiation period and the quantity and quality of sperm (see
Chapter 2).
The most used method until now in this species, which involves the weekly
injection of hCG (1.5 IU g -1 fish) under a constant thermal regime of 20 ºC
(Pérez et al., 2000), has previously shown successful spermiation results in
closely related species such as the Japanese eel (Anguilla japonica; Ohta el
al., 1997), American eel (Anguilla rostrata; Sorensen and Winn, 1984) or
New Zealand eel (Anguilla australis; Todd, 1981), thus that treatment is
able to induce in an effective way both spermatogenesis and
spermiogenesis in eel species.
The results obtained in this study using this standard treatment agree with
previously published reproductive data on European eel such as the onset
of spermiation, the percentage of spermiating males or sperm volume
(Asturiano et al., 2005; Pérez et al., 2000). However, the total motility
values from our experiment (described in Chapter 2) were much higher
than those obtained in previous studies where an identical maturation
method had been applied. In this respect, numerous factors such as i) the
variability between eel batches, ii) the hormone provider, and especially iii)
the way of evaluating the sperm samples (subjective against objective
methods) could explain these differences. Nowadays, thanks to the use of
an objective and accurate previously standardized CASA system (see
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