Abstract
AbstractThe lifespan of spermatozoa from externally fertilizing freshwater fish ranges from a few seconds to several minutes, depending on the species. External factors, such as temperature, background flows and ion composition, play an important role in fertilization success. Specific mechanisms guiding spermatozoa appear to be essential to maximize the sperm–egg encounter under these strenuous conditions. Although some existing data support the hypothesis that both the ovarian fluid and the eggs may release chemoattractants that significantly affect spermatozoa behaviour and the fertilization outcome, this hypothesis is still open to debate, as the existence of freshwater fish spermatozoa chemotaxis has yet to be demonstrated; in addition, specific mechanisms supporting spermatozoa guidance and gamete selection have not been elucidated. Is the natural selection of gametes determined by a combination of different physicochemical phenomena? Alternatively, is the natural selection of species‐specific gametes biased towards the species‐specific guidance mechanisms of their natural landscape? These questions have received more attention as new studies have revealed potential, distinct guidance mechanisms in freshwater fish reproduction. In this review, we discuss the empirical studies supporting different hypotheses about freshwater fish gamete guidance and highlight the synergistic combination of experiments and biomathematical modelling to explore these questions. Finally, we discuss the challenges in understanding the mechanisms behind sperm guidance in freshwater fish species, and we suppose that knowledge about the mechanisms that underlie spermatozoa selection and guidance in freshwater fish species may elucidate the impact of the traditional aquaculture practice of artificial fertilization on progeny quality and species sustainability.
Highlights
Darwinian evolution permeates all life forms on our planet
This review is organized as follows: in the first section, we present an overview of the basic morphological and physiological features of freshwater fish gametes, including the maturation conditions of gamete activation, and the environmental effects on sperm motility, that is, the conditions crucial for the proper function of fish gametes that are apparently necessary for the sperm–egg encounter; in the second section, we introduce the feasibility of the specific mechanisms underlying the guidance of spermatozoa towards the eggs in the light of freshwater fish reproductive behaviour and the theories on gamete encounters
Proteinaceous or peptidic sperm-activating factors have been identified in ovarian fluid or among the substances released by the eggs of sea urchins, jellyfish (Hippopodius hippopus; Cosson et al 1986), starfish (Asterias amurensis; Nishigaki et al 1996), herring (C. pallasi; Morisawa et al 1992; Pillai et al 1993; Oda et al 1995) and newts (Cynops pyrrhogaster) (Watanabe et al 2010) (Table 2)
Summary
Darwinian evolution permeates all life forms on our planet. For most species from Animalia, natural selection begins with the successful swapping of genetic material following fertilization, where an embryo is formed and developed, and if the embryo is sufficiently healthy, it grows and reaches maturity to reproduce before dying (Pelegri et al 2017). Spermatozoa guidance in freshwater fish part of this section is devoted to the specific site where the sperm cell could enter the egg, the micropyle: the existing data on its physical and chemical cues for the male gametes are presented.
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
