Search results
Results From The WOW.Com Content Network
Ovuliparity means the female lays unfertilised eggs (ova), which must then be externally fertilised. [10] Examples of ovuliparous fish include salmon, goldfish, cichlids, tuna and eels. In the majority of these species, fertilisation takes place outside the mother's body, with the male and female fish shedding their gametes into the surrounding ...
Fisheries-induced evolution differs from the Darwinian evolution model by virtue of the direct human factor. [2] For FIE, fishing enforces a greater selection pressure for traits, often through sheer effort and catch numbers, which can disparage natural selection pressures such as predator-prey interactions and environmental influences.
Selective breeding (also called artificial selection) is the process by which humans use animal breeding and plant breeding to selectively develop particular phenotypic traits (characteristics) by choosing which typically animal or plant males and females will sexually reproduce and have offspring together.
For example, the Mexican tetra is an albino cavefish that lost its eyesight during evolution. Breeding together different populations of this blind fish produced some offspring with functional eyes, since different mutations had occurred in the isolated populations that had evolved in different caves. [243]
Jawless fish belong to the superclass Agnatha in the phylum Chordata, subphylum Vertebrata. Agnatha means 'un-jawed, without jaws' (from Ancient Greek). [11] It excludes all vertebrates with jaws, known as gnathostomes. Although a minor element of modern marine fauna, jawless fish were prominent among the early fish in the early Paleozoic.
The evolution for semelparity in both sexes has occurred many times in plants, invertebrates, and fish. It is rare in mammals because mammals have obligate maternal care due to internal fertilization and incubation of offspring and nursing young after birth, which requires high maternal survival rate after fertilization and offspring weaning .
Nuptial tubercles or breeding tubercles (also called pearl organs or nuptial efflorescence) are noticeable skin roughness or horny nodules that form on male fish during breeding. They are made of keratin, the same material as hair, hooves, and fingernails.
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 ...