There are two types of viviparity, differentiated by how the offspring gain their nutrients. Although true viviparity has been described in the African frog Nectophrynoides, most amphibians lay eggs. Social behavior is a common phenomenon among vertebrates, notably in fish, birds and mammals. Corpora lutea are found only in mammals, and in some elasmobranch fish; in other species, the remnants of the follicle are quickly resorbed by the ovary. Ovuliparity means the female lays unfertilised eggs (ova), which must then be externally fertilised. However, inbreeding avoidance mechanisms that operate subsequent to copulation are less well known. Aquarists commonly refer to ovoviviparous and viviparous fish as livebearers. Several behavioral responses have.  In oviparous fish, internal fertilisation requires the male to use some sort of intromittent organ to deliver sperm into the genital opening of the female. The ampullae are otherwise essentially identical to the seminiferous tubules in higher vertebrates, including the same range of cell types.  Gymnovaries are the primitive condition found in lungfish, sturgeon, and bowfin. The larval period in oviparous fish is relatively short (usually only several weeks), and larvae rapidly grow and change appearance and structure (a process termed metamorphosis) to become juveniles. The skinks and a number of other lizards are known to guard their eggs. Cystovaries characterize most teleosts, where the ovary lumen has continuity with the oviduct. The act of mating in sharks usually includes raising one of the claspers to allow water into a siphon through a specific orifice. REPRODUCTIVE BIOLOGY IN FISHES 2. In general, the reproductive behaviour of snakes is not well known. Examples include the oviparous sharks, such as the horn shark, and oviparous rays, such as skates. However, the alternative reproductive tactics of the cichlid,Pseudocrenilabrus philander, appear to have unequal payoffs. However, the alternative reproductive tactics of the cichlid, Pseudocrenilabrus philander, appear to have unequal payoffs. In the European newt Triturus, for example, in which mating takes place in the water, the male places himself in front of a female with his back to her.  Embryo viability was significantly reduced in inbred exposed fish and there was a tendency for inbred males to sire fewer offspring. The clasper is then inserted into the cloaca, where it opens like an umbrella to anchor its position. One-day-old Siamese fighting fish larvae in a bubble nest - their yolk sacs have not yet been absorbed, A 15-day-old free-swimming fry of a Siamese fighting fish, Salmon eggs in different stages of development. Thierry Lodé described reproductive strategies in terms of the development of the zygote and the interrelationship with the parents; there are five classifications - ovuliparity, oviparity, ovo-viviparity, histotrophic viviparity and hemotrophic viviparity.. Oviparity is where fertilisation occurs internally and so the female sheds zygotes (or newly developing embryos) into the water, often with important outer tissues added. Marine fish can produce high numbers of eggs which are often released into the open water column. The elkhorn sculpin (Alcichthys elongatus) is a marine teleost with a unique reproductive mode called “internal gametic association”. Whereas the developing gonads of all other vertebrates have an outer and inner layer of tissue, those of bony fishes have a simple origin that lacks any male or female elements. Most fish are gonochorists, but hermaphroditism is known to occur in 14 families of teleost fishes.. Most male fish have two testes of similar size. A significant effect of inbreeding depression on juvenile survival was also found, but only in high-density competitive environments, suggesting that intra-specific competition can magnify the deleterious effects of inbreeding. 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. , Although inbreeding, especially in the extreme form of self-fertilization, is ordinarily regarded as detrimental because it leads to expression of deleterious recessive alleles, self-fertilization does provide the benefit of fertilization assurance (reproductive assurance) at each generation.. Even air-breathing amphibians lay their eggs in water, or in protective foam as with the Coast foam-nest treefrog, Chiromantis xerampelina. These are seasonal structures, releasing their contents during the breeding season, and then being reabsorbed by the body. Sperm are introduced into the ovary by copulation and then enter the micropylar canal of ovulated eggs in the ovarian cavity. The males of some snakes have characteristic skin papillae (nipple-like projections) on the throat; the fact that they rub the papillae over the female’s body suggests that tactile stimuli are also important to reproduction. A special case of parthenogenesis is gynogenesis. HORMONAL CONTROL OF BEHAVIOUR IN STICKLEBACKS 1503 TABLE 2. The adoption of either the territorial or the sneaking option in the cichlid fish is dictated by social conditions within the hierarchy.  In addition to the physiological adaptations, the immune system is altered to allow the conjoining. Cartilagenous fish (sharks, skates, rays, chimaeras) eggs are fertilized internally and exhibit a wide variety of both internal and external embryonic development. , Many of the features found in ovaries are common to all vertebrates, including the presence of follicular cells and tunica albuginea There may be hundreds or even millions of fertile eggs present in the ovary of a fish at any given time. Arquivos do Museu Nacional, Rio de Janeiro, 61 (4): 241-244. Exposure of zebra fish to a chemical environmental agent, analogous to that caused by anthropogenic pollution, amplified the effects of inbreeding on key reproductive traits. In some species, the gonopodium may be half the total body length.  Secondary gymnovaries are found in salmonids and a few other teleosts. In many species of fish, fins have been modified to allow Internal fertilisation. The sperm is preserved in the female's oviduct. Ambisexual Fishes Reproductive Behaviour. In order to investigate this question further, Pall et al. Oxygen levels of the water, availability of food, size of each fish, age, number of times the fish has spawned before and water temperature are all factors known to effect when and how many eggs each carp will spawn at any one time.