Agriculture Reference
In-Depth Information
12.4 REPRODUCTION AND METABOLISM
Broodstock nutrition is without doubt one of the most poorly understood and poorly researched
areas of finfish nutrition. To a large extent, this has been due to the necessity of suitable indoor
or outdoor culture facilities for maintaining large groups of adult fish and the consequent logis-
tical challenges and higher cost of running and conducting extended broodstock feeding trials.
As in other animals, it is also clear that many of the deficiencies and problems encountered
during the early rearing phases of newly hatched finfish larvae are directly related to the feed-
ing regime (including the nutrient level and quality) provided to the broodstock. At present, for
most cultured fish species, many of the commercially available so-called 'broodstock diets' are
just larger sized on-growing diets. In practice, many marine fish hatcheries improve the nutri-
tion of their broodstock by feeding them solely on fresh marine byproducts or in combination
with commercial diets.
Despite the lack of specific nutritional understanding in this context, the consequences of
nutrition on reproduction are well known and widely reported (Izquierdo
etal.
2001; Watanabe
and Vassallo-Agius 2003; Bobe and Labbe 2010). Nutrition affects all aspects of reproductive
events, from pubescence to gametogenesis, in both males and females. The explanation for
this close association between nutrition and reproduction is to guarantee that the reproductive
event will be intimately aligned with the nutrient supply to assure the survival of new progeny
(Scaramuzzi
etal.
2006). Food restriction itself can seriously affect spawning success. A reduc-
tion in feeding rate has been reported to cause an inhibition of gonadal maturation in several
fish species, including goldfish (
Carassius auratus
) (Sasayama and Takahashi 1972), Euro-
pean sea bass (
Dicentrarchus labrax
)(CerdÃ
et al.
1994) and male Atlantic salmon (
Salmo
salar
L.) (Berglund 1995).
Reduced fecundity, as reported in several marine fish species, could be caused either by
the restriction in the availability of biochemical components for egg formation or by the influ-
ence of a nutrient imbalance on the brain-pituitary-gonad endocrine system. In fact, in recent
years it has been well established that the process of GnRH transcription and secretion is gated
by the state of energy reserves in the organism (Hill
et al.
2008) and is sensitive to different
metabolic cues. The neuroendocrine mechanisms responsible for the tight coupling between
energy homeostasis and fertility are represented by metabolic hormones and neuropeptides
which integrate and interplay at different levels with the HPG axis governing reproduction
(Fernandez-Fernandez
et al.
2006; Castellano
et al.
2008; Kitahashi
et al.
2008; Zohar
et al.
2010). The impact of energy status on the reproductive axis is conveyed through a number of
neuropeptide hormones such as KiSS1 and KiSS2, and peripheral metabolic signals, such as
leptin, whose nature and mechanisms of action have begun to be deciphered only in recent
years in mammals and, to a lesser extent, in fish (Fernandez-Fernandez
et al.
2006; Castellano
et al.
2008; Kitahashi
et al.
2008). In 2003, the understanding of the regulation of repro-
duction and puberty was revolutionized by the discovery of the KiSS1/GPR54 system (de
Roux
et al.
2003; Seminara
et al.
2003). It is now confirmed that KiSS1/GPR54 signalling
is central to the regulation of GnRH and consequently to LH and FSH secretion, as well as
being implicated in a growing list of key biological functions including nutrition, metabolism
and response to photoperiodicity (Revel
et al.
2006; Roa and Tena-Sempere 2007; Carnevali
et al.
2011). Recently, studies have reported the identification and characterization of a KiSS1
gene from zebrafish
Danio rerio
(van Aerle
et al.
2008) and medaka
Oryzias latipes
(Kanda
et al.
2008). Furthermore, recent studies indicate the presence of two genes encoding different
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