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Most male fish have two testes of similar size. In the case of sharks, the testes on the right side is usually larger [citation needed].The primitive jawless fish have only a single testis, located in the midline of the body, although even this forms from the fusion of paired structures in the embryo.
A gonad, sex gland, or reproductive gland [1] is a mixed gland and sex organ that produces the gametes and sex hormones of an organism. Female reproductive cells are egg cells, and male reproductive cells are sperm. [2] The male gonad, the testicle, produces sperm in the form of spermatozoa. The female gonad, the ovary, produces egg cells
A small portion of fish species are either viviparous or ovoviviparous, and are collectively known as livebearers. [23] Fish gonads are typically pairs of either ovaries or testicles. Most fish are sexually dimorphic but some species are hermaphroditic or unisexual. [24]
Free-living males and unparasitized females in these species never have fully developed gonads. Thus, males never mature without attaching to a female, and die if they cannot find one. [4] At birth, male ceratioids are already equipped with extremely well-developed olfactory organs that detect scents in the water. Males of some species also ...
Sea urchins are dioecious, having separate male and female sexes, although no distinguishing features are visible externally. In addition to their role in reproduction, the gonads are also nutrient storing organs, and are made up of two main type of cells: germ cells, and somatic cells called nutritive phagocytes. [20]
Juvenile fish can be either male, known as a primary male, or female. Females transition into male fish, known as secondary males, at a length of between 45 and 60 cm (18 and 24 in). Secondary males can be told from primary males by examination of their gonads. [5] The male digs a burrow and guards the nest. [2]
This includes defending a certain territory by refusing to cede it to a potential love rival, or a human fisher, or returning to a threatened territory more quickly than less fit male fish ...
For example, male testes of spawning fish are smooth and white and account for up to 12% of the mass of the fish, while female ovaries are granular and orange or yellow, accounting for up to 70% of the fish's mass. Male lampreys, hagfish and salmon discharge their sperm into the body cavity where it is expelled through pores in the abdomen.