Oogenesis and Egg Quality in Finfish: Yolk Formation and Other Factors Influencing Female Fertility

Abstract

Egg quality in fishes has been a topic of research in aquaculture and fisheries for decades as it represents an important life history trait and is critical for captive propagation and successful recruitment. A major factor influencing egg quality is proper yolk formation, as most fishes are oviparous and the developing offspring are entirely dependent on stored egg yolk for nutritional sustenance. These maternally derived nutrients consist of proteins, carbohydrates, lipids, vitamins, minerals, and ions that are transported from the liver to the ovary by lipoprotein particles including vitellogenins. The yolk composition may be influenced by broodstock diet, husbandry, and other intrinsic and extrinsic conditions. In addition, a number of other maternal factors that may influence egg quality also are stored in eggs, such as gene transcripts, that direct early embryonic development. Dysfunctional regulation of gene or protein expression may lead to poor quality eggs and failure to thrive within hours of fertilization. These gene transcripts may provide important markers as their expression levels may be used to screen broodstock for potential spawning success. In addition to such intrinsic factors, stress may lead to ovarian atresia or reproductive failure and can impact fish behavior, fecundity, and ovulation rate. Finally, postovulatory aging may occur when eggs become overripe and the fish fails to spawn in a timely fashion, leading to low fertility, often encountered during manual strip spawning of fish.

Effects of estradiol and 11-ketotestosterone pre-treatment on artificial induction of maturation in silver female shortfinned eels (Anguilla australis)

“…Estradiol pre-treated eels induced to mature may therefore be more closely resembling naturally maturing eels and arguably, may sequester more appropriate amounts of vitellogenin. Given the links between appropriate yolk formation and egg quality (reviewed in: [52]), and the low quality of eggs produced by standard hypophysation protocols, comparing vitellogenin content in the eggs stripped from E 2 treated fish to that in eggs from SPH only treated fish seems worthwhile.…”

Early gonadal maturation and vitellogenin mRNA expression in Siberian sturgeon Acipenser baerii cultured in a semi-closed water recirculating system in Korea

“…It is similar with the elevated vitellogenin expression in accordance with either gonadal development or reproductive cycle, which has been observed not only in this chondrostean fish group but in other teleost species (Amberg et al, 2010;Zhang et al, 2011a;Hara et al, 2016;Fajkowska et al, 2016). In early works, vitellogenin has been originally thought as a mature female-specific protein since it is the main proteinogenic component of fish yolk, however, a number of subsequent studies have indicated that the transcription of vitellogenin gene is active also in both males and sexually immature fishes (Arukwe and Goksøyr, 2003;Zhang et al, 2005;Reading et al, 2018). Similarly, in this study, Siberian sturgeon males robustly display hepatic vitellogenin transcripts of which expression levels are readily comparable to those observed in females or even higher than in females in a certain life interval.…”

Histological characterization of the maturation stages of the ovarian follicles of the goldfish Carassius auratus (Linnaeus, 1758)

“…In a joint "oil droplet and cortical alveoli step," the lipidic accumulation can be massive with time, pushing cortical alveoli to a thin subplasmalemmal strip, as observed in the goodeids Crenichthys baileyi and Empetrichthys latos (Uribe et al, 2012). The emergence and build-up of lipid droplets in most teleosts phenotypically translate what is presently called "oocyte lipidation" (Reading et al, 2018). Like the goldfish, the zebrafish does not display lipid droplets in oocytes, despite accumulating lipids in yolk (Malone & Hisaoka, 1963;Selman, Wallace, Sarka, & Qi, 1993).…”