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Fish reproduction. A pair of bettas spawning under a bubble nest. Fish reproductive organs include testes and ovaries. In most species, gonads are paired organs of similar size, which can be partially or totally fused. [1] There may also be a range of secondary organs that increase reproductive fitness.
Pregnancy in fish. Appearance. A pregnant Southern platyfish. Pregnancy has been traditionally defined as the period of time eggs are incubated in the body after the egg-sperm union. [ 1 ] Although the term often refers to placental mammals, it has also been used in the titles of many international, peer-reviewed, scientific articles on fish, e ...
This type of reproduction had been seen before in bony fish, but not in cartilaginous fish such as sharks. [71] In the same year, a female Atlantic blacktip shark in Virginia reproduced via parthenogenesis. [72] On 10 October 2008, scientists confirmed the second case of a "virgin birth" in a shark.
Reproduction is costly for anadromous salmonids, because their life history requires transition from saltwater to freshwater streams, and long migrations, which can be physiologically taxing. The transition between cold oceanic water to warm freshwater and steep elevation changes in Northern Pacific rivers could explain the evolution of ...
The evolution of fish began about 530 million years ago during the Cambrian explosion. It was during this time that the early chordates developed the skull and the vertebral column, leading to the first craniates and vertebrates. The first fish lineages belong to the Agnatha, or jawless fish.
Marine animals, and particularly bony fish, commonly reproduce by broadcast spawning. This is an external method of reproduction where the female releases many unfertilised eggs into the water. At the same time, a male or many males release a lot of sperm into the water which fertilises some of these eggs.
Fish embryos go through a process called mid-blastula transition which is observed around the tenth cell division in some fish species. Once zygotic gene transcription starts, slow cell division begins and cell movements are observable. [4] During this time three cell populations become distinguished. The first population is the yolk syncytial ...
One fish species does not reproduce by sexual reproduction but uses sex to produce offspring; Poecilia formosa is a unisex species that uses a form of parthenogenesis called gynogenesis, where unfertilized eggs develop into embryos that produce female offspring.