Reproductive Organs

(Main goal = elaborate more on sex determination and sex differentiation of fish, add hyperlinks, add bowfin reproductive anatomy picture)

Underlined = edits I wish to add

Fish reproductive organs include testes and ovaries. In most species, gonads are paired organs of similar size, which can be partially or totally fused.[42] There may also be a range of secondary organs that increase reproductive fitness. The genital papilla is a small, fleshy tube behind the anus in some fishes from which the sperm or eggs are released; the sex of a fish often can be determined by the shape of its papilla. Sex determination in fish, which is dependent on intrinsic genetic factors, is followed by sex differentiation through gene expression of feedback mechanisms that ensure the stability of the levels of particular hormones and cellular profile. However, the hermaphroditic species are an exception in which they are able to alter the course of sex differentiation in order to maximize their fitness. There are various determination mechanisms for gonadal sex in fish and processes that aid development of the gonadal function. Gonadal sex is influenced by a number of factors, including cell-autonomous genetic mechanisms, endocrine, paracrine, behavioral, or environmental signals. This results in the primordial germ cells (PGCs) to be able to interpret internal or external stimuli to develop into spermatogonia or oogonia.^[1]Spermatogenesis in testes is a process in which spermatogonia differentiates into spermatocytes through mitosis and meiosis, which halves the number of chromosomes, creating haploid spermatids. During spermiogenesis, the last stage of spermatogenesis, the haploid spermatids develop into spermatozoa.^[2] In the ovaries, oogonia also undergo mitosis and meiosis during oogenesis, and this gives rise to primary oocytes and then eventually the ovum. The primary oocyte divides and produces the secondary oocyte as well as a polar body, before the secondary oocyte develops into the haploid ootid.^[3]

^ Devlin, Robert H.; Nagahama, Yoshitaka (2002-06-21). "Sex determination and sex differentiation in fish: an overview of genetic, physiological, and environmental influences". Aquaculture. Sex determination and sex differentation in fish. 208 (3): 191–364. doi:10.1016/S0044-8486(02)00057-1. ISSN 0044-8486.
^ Nishimura, Hitoshi; L’Hernault, Steven W. (2017-09-25). "Spermatogenesis". Current Biology. 27 (18): R988–R994. doi:10.1016/j.cub.2017.07.067. ISSN 0960-9822.
^ Sánchez, Flor; Smitz, Johan (2012-12-01). "Molecular control of oogenesis". Biochimica et Biophysica Acta (BBA) - Molecular Basis of Disease. Molecular Genetics of Human Reproductive Failure. 1822 (12): 1896–1912. doi:10.1016/j.bbadis.2012.05.013. ISSN 0925-4439.

[1] Devlin, Robert H.; Nagahama, Yoshitaka (2002-06-21). "Sex determination and sex differentiation in fish: an overview of genetic, physiological, and environmental influences". Aquaculture. Sex determination and sex differentation in fish. 208 (3): 191–364. doi:10.1016/S0044-8486(02)00057-1. ISSN 0044-8486.

[2] Nishimura, Hitoshi; L’Hernault, Steven W. (2017-09-25). "Spermatogenesis". Current Biology. 27 (18): R988–R994. doi:10.1016/j.cub.2017.07.067. ISSN 0960-9822.

[3] Sánchez, Flor; Smitz, Johan (2012-12-01). "Molecular control of oogenesis". Biochimica et Biophysica Acta (BBA) - Molecular Basis of Disease. Molecular Genetics of Human Reproductive Failure. 1822 (12): 1896–1912. doi:10.1016/j.bbadis.2012.05.013. ISSN 0925-4439.

[1]

[2]

[3]