A Review on the Reproductive Dysfunction in Farmed Finfish

Globally, fish production in the wild is decreasing, and different aquaculture systems are presently being used for broodstock development in the captivity. Seasonally, broodstock raised in captivity exhibit different form of reproductive dysfunction at the level of the brain-pituitary-gonad (BPG) axis. Primarily, vitellogenic completion and final oocyte maturation are inhibited in females, and males fail to spermiate spontaneously in the captivity. Reproductive dysfunctions are also observed during sexual differentiation, pubertal onset and sex conversion periods in teleosts. To overcome these problems, different hormonal preparations, primarily gonadotropin-releasing hormones (GnRH) are used. In recent years, kisspeptins have been shown to be potent in inducing gonadal growth and maturation in teleost fish. Understanding the form of reproductive dysfunction is important in formulating suitable hormonal preparations for inducing gametogenesis. The paper reviews the problem of reproductive dysfunction and their possible reason for formulating different hormonal preparations.

Gonads or body? Differences in gonadal and somatic photoperiodic growth response in two vole species

ABSTRACTTo optimally time reproduction, seasonal mammals use a photoperiodic neuroendocrine system (PNES) that measures photoperiod and subsequently drives reproduction. To adapt to late spring arrival at northern latitudes, a lower photoperiodic sensitivity and therefore a higher critical photoperiod for reproductive onset is necessary in northern species to arrest reproductive development until spring onset. Temperature–photoperiod relationships, and hence food availability–photoperiod relationships, are highly latitude dependent. Therefore, we predict PNES sensitivity characteristics to be latitude dependent. Here, we investigated photoperiodic responses at different times during development in northern (tundra or root vole, Microtus oeconomus) and southern vole species (common vole, Microtus arvalis) exposed to constant short (SP) or long photoperiod (LP). Although the tundra vole grows faster under LP, no photoperiodic effect on somatic growth is observed in the common vole. In contrast, gonadal growth is more sensitive to photoperiod in the common vole, suggesting that photoperiodic responses in somatic and gonadal growth can be plastic, and might be regulated through different mechanisms. In both species, thyroid-stimulating hormone β-subunit (Tshβ) and iodothyronine deiodinase 2 (Dio2) expression is highly increased under LP, whereas Tshr and Dio3 decrease under LP. High Tshr levels in voles raised under SP may lead to increased sensitivity to increasing photoperiods later in life. The higher photoperiodic-induced Tshr response in tundra voles suggests that the northern vole species might be more sensitive to thyroid-stimulating hormone when raised under SP. In conclusion, species differences in developmental programming of the PNES, which is dependent on photoperiod early in development, may form different breeding strategies as part of latitudinal adaptation.

Gonads or body? Differences in gonadal and somatic photoperiodic growth response in two vole species

To optimally time reproduction, seasonal mammals use a photoperiodic neuroendocrine system (PNES) that measures photoperiod and subsequently drives reproduction. To adapt to late spring arrival at northern latitudes, a lower photoperiodic sensitivity and therefore a higher critical photoperiod for reproductive onset is necessary in northern species to arrest reproductive development until spring onset. Temperature-photoperiod relationships, and hence food availability-photoperiod relationships, are highly latitude dependent. Therefore, we predict PNES sensitivity characteristics to be latitude-dependent. Here, we investigated photoperiodic responses at different times during development in northern- (tundra/root vole, Microtus oeconomus) and southern vole species (common vole, Microtus arvalis) exposed to constant short (SP) or long photoperiod (LP).M. oeconomus grows faster under LP, whereas no photoperiodic effect on somatic growth is observed in M. arvalis. Contrastingly, gonadal growth is more sensitive to photoperiod in M. arvalis, suggesting that photoperiodic responses in somatic and gonadal growth can be plastic, and might be regulated through different mechanisms. In both species, thyroid-stimulating-hormone-β subunit (Tshβ) and iodothyronine-deiodinase 2 (Dio2) expression is highly increased under LP, whereas Tshr and Dio3 decreases under LP. High Tshr levels in voles raised under SP may lead to increased sensitivity to increasing photoperiods later in life. The higher photoperiodic induced Tshr response in M. oeconomus suggests that the northern vole species might be more sensitive to TSH when raised under SP.Species differences in developmental programming of the PNES, which is dependent on photoperiod early in development, may form part divergent breeding strategies evolving as part of latitudinal adaptation.Summary statementDevelopment of the neuroendocrine system driving photoperiodic responses in gonadal and somatic growth differ between the common and the tundra vole, indicating that they use a different breeding strategy.