Can Probiotics Affect Reproductive Processes of Aquatic Animals? - Aquaculture Nutrition: Gut Health, Probiotics and Prebiotics - page 331

2009) leading to maturation promoting factor (MPF) formation, by the binding and activation
of two subunits, cyclin B and cdc2 (Figure 12.2) (Yoshikuni and Nagahama 1994; Yamashita
1998; 2000; Nagahama and Yamashita 2008).
When maturation is complete the oocyte is expelled from the follicle. The ovulated oocyte
(now properly termed egg) becomes fertilizable (Nagahama et al. 1994; 1995; Khan and
Thomas 1999), traverses the oviducts to the gonopore, and is expelled during the next spawning
event (Connaughton and Aida 1999).
12.3 BROODSTOCK REPRODUCTIVE DYSFUNCTIONS
Reproductive problems are usually more serious in female broodstocks and can be classified
into three types depending on which phase of the reproductive cycle is affected.
The first and most severe reproductive dysfunction, which is fortunately restricted to a lim-
ited number of species, affects the vitellogenic phase. This problem occurs in freshwater eel
( Anguilla spp.) which fail to undergo vitellogenesis when maintained in captivity. Other fish
species with a similar problem include the Mediterranean amberjack ( Seriola dumerili ), a
species of great interest for the aquaculture industry (Abellan and Basurco 1999), and the
grey mullet ( Mugil cephalus ) (de Monbrison et al. 1997).
Another type of reproductive dysfunction affecting cultured females is the lack of final
oocyte maturation. At the onset of the spawning season, the post-vitellogenic oocytes fail to
undergo maturation and ovulation becoming atretic (Tucker 1994; Berlinsky et al. 1997; Lars-
son et al. 1997; Mylonas et al. 1997a; 1997b). This is the most common type of reproductive
problem encountered in aquaculture and a great deal of research has been focused on this issue
(Mylonas et al. 2010).
The last type of reproductive dysfunction of female broodstocks is the failure to deliver
the ovulated eggs into the water at the end of the reproductive cycle (i.e. failure to spawn).
In salmonids, eggs are retained in the abdominal cavity and reabsorbed over the following
months (Bromage et al. 1992). Females of some marine species, like the striped bass ( Morone
spp.), common dentex ( Dentex dentex ) and white grouper ( Epinephelus aeneus ) may release
these eggs at a later time after ovulation (Hassin et al. 1997).
For the species presenting these reproductive dysfunctions, the aquaculture industry has
dealt with this trouble for many years, nearly exclusively by collecting juveniles or adults
directly from the wild, but this conduct is unreliable and unpredictable, and thus inappropriate
for industrial scale aquaculture. Additionally, to improve the reliability of spawning, manipu-
lations of various environmental parameters, such as temperature, photoperiod, salinity, tank
volume and depth, and substrate vegetation are undertaken (Zohar et al. 1989; Munro et al.
1990; Yaron 1995). However, in some species such as cyprinids (Kaminski etal. 2004), catfish
(Wen and Lin 2004) and mullets (Aizen et al. 2005), hormonal treatments are used to control
reproduction and, over the years, a variety of hormonal approaches have been successfully
applied (Mylonas et al. 2010).
Finally, more recently an improvement in broodstock nutrition and alimentation has been
shown to greatly enhance gamete quality and offspring production, because a large number
of dietary nutrients such as proteins, vitamins and fatty acids affect gonadal development and
fecundity, particularly in continuous spawners with short vitellogenesis (Izquierdo et al. 2001;
Watanabe and Vassallo-Agius 2003; Bobe and Labbe 2010).