Broodstock management and hormonal manipulations of fish reproduction

Abstract

Control of reproductive function in captivity is essential for the sustainability of commercial aquaculture production, and in many fishes it can be achieved by manipulating photoperiod, water temperature or spawning substrate. The fish reproductive cycle is separated in the growth (gametogenesis) and maturation phase (oocyte maturation and spermiation), both controlled by the reproductive hormones of the brain, pituitary and gonad. Although the growth phase of reproductive development is concluded in captivity in most fishes-the major exemption being the freshwater eel (Anguilla spp.), oocyte maturation (OM) and ovulation in females, and spermiation in males may require exogenous hormonal therapies. In some fishes, these hormonal manipulations are used only as a management tool to enhance the efficiency of egg production and facilitate hatchery operations, but in others exogenous hormones are the only way to produce fertilized eggs reliably. Hormonal manipulations of reproductive function in cultured fishes have focused on the use of either exogenous luteinizing hormone (LH) preparations that act directly at the level of the gonad, or synthetic agonists of gonadotropin-releasing hormone (GnRHa) that act at the level of the pituitary to induce release of the endogenous LH stores, which, in turn act at the level of the gonad to induce steroidogenesis and the process of OM and spermiation. After hormonal induction of maturation, broodstock should spawn spontaneously in their rearing enclosures, however, the natural breeding behavior followed by spontaneous spawning may be lost in aquaculture conditions. Therefore, for many species it is also necessary to employ artificial gamete collection and fertilization. Finally, a common question in regards to hormonal therapies is their effect on gamete quality, compared to naturally maturing or spawning broodfish. The main factors that may have significant consequences on gamete quality-mainly on eggs-and should be considered when choosing a spawning induction procedure include (a) the developmental stage of the gonads at the time the hormonal therapy is applied, (b) the type of hormonal therapy, (c) the possible stress induced by the manipulation necessary for the hormone administration and (d) in the case of artificial insemination, the latency period between hormonal stimulation and stripping for in vitro fertilization.

Molecular basis and genetic improvement of economically important traits in aquaculture animals

“…In this cascade, gonadotropin-releasing hormones (GnRHs) produced by hypothalamus are found to be the primary neuropeptides, and gonadotropic hormones (GtHs) synthesized and released by pituitary are found to lead ovaries or testicles to produce mature eggs or sperms, whereas dopamine (DA) produced by pituitary has been found to exhibit an inhibiting effect on the functions of GnRHs [62][63][64]. Multiple GtHs have been reported by Chinese scientists in groupers [65] and Chinese sturgeon (Acipenser sinensis) [66].…”

Caracterização macroscópica das gônadas durante a reprodução induzida em cativeiro do surubim-do-paraíba

“…No entanto, a baixa produção de ovos obtida durante a indução artificial, se comparada com a de outros Siluriformes (Leonardo et al, 2004;Baldisserotto & Radünz Neto, 2005), sugere a necessidade de um estudo específico nos ovários durante o período de indução hormonal desta espécie. A hipótese seria que a manipulação hormonal e a manutenção em cativeiro possam estar de alguma forma prejudicando a ovulação ou a desova, como já descrito na literatura para outras espécies (Mylonas et al, 2010).…”

“…A quantidade de ovócitos liberados por fêmea foi baixa, se comparada à quantidade liberada pelos animais de origem selvagem, de 40 e 60 g por fêmea (Caneppele et al, 2009), e por outros Siluriformes, como Pseudoplatystoma fasciatum (Leonardo et al, 2004) e Steindachneridion melanodermatum (Ludwig et al, 2005). A indução hormonal e o procedimento de extrusão dos gametas podem causar impactos negativos à qualidade destes, e também podem influenciar a taxa de fertilização, como sugerido para outras espécies de teleósteos (Mylonas et al, 2010).…”

Desova induzida de curimatã-pacu submetido a dois protocolos de hipofisação

“…Entretanto, o manejo excessivo dos animais decorrente deste protocolo pode causar estresse, e prejudicar a qualidade dos ovócitos, e a morte destes (Schreck et al, 2001;Mylonas et al, 2010;Zohar et al, 2010). Além disso, o tempo de permanência dos reprodutores dentro do laboratório pode acarretar custos relacionados ao consumo de água e energia elétrica O curimatã-pacu (Prochilodus argenteus Agassiz, 1829) é endêmico da Bacia do Rio São Francisco e, também, é popularmente conhecido por xira, bambá ou zulega (Castro & Vari, 2003).…”

“…O modelo final das relações entre HGE e demais variáveis foi representado pela equação HGE = e 5,72P1 + 5,44P2 (R 2 = 0,9999), o que indicou que apenas os protocolos utilizados influenciaram a HGE (p<0,05). Este aspecto está associado ao desenvolvimento gonadal das fêmeas selecionadas, considerando-se que doses prévias têm a função de incrementar a maturação final dos ovócitos e sincronizar o estádio maturacional para aplicar uma dose decisiva (Mylonas et al, 2010).…”