Artificial insemination and gamete management in fish

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Abstract
Artificial insemination (the collection of spermatozoa and ova and their mixing together in various media that keep spermatozoa motile) is carried out in only a few species (mostly freshwater), such as salmonids, cyprinids and acipenserids. Traditionally, fresh water (or sea water for marine species) is used as the medium in which the male and female gametes are mixed. However, fresh water is not a very favourable medium because hypotonic shock causes the sperm structure to deteriorate in several minutes and the egg is activated quickly. These problems can be avoided by using as media various saline solutions of different composition, depending on the species (125 mM NaCl pH 9 for salmonids; 50 raM Nacl pH 8 for cyprinids). These media prevent sperm deterioration, prolong slightly the duration of motility, and prevent or defer the cortical reaction. These solutions also prevent the yolk of crushed eggs from precipitating when it comes into contact with the water, limit motility and block the micropyle. Fish farmers are beginning to use these media, so significantly increasing the fertilization rate while reducing the number of spermatozoa used for insemination. The length of gamete survival is an important factor to consider in carrying out artificial reproduction. Gamete survival in vivo (after the release of sperm and oocytes from cysts and follicles) varies with the species. Sperm fertilizing ability decreases during the spawning period in sea bass and trout but not in carp. Ovum survival in the general or ovarian cavity is from one to several weeks in salmonids, several hours in carp at 20°C and only 30 min in Chinese carp. In vitro survival is from one to several weeks for sperm (under oxygen and with antibiotics added) and several hours for ova (2–4 h in carp and 12–24 h in trout). The spermatozoa of several species of teleosts have been stored deep frozen, but the quality of the sperm is not as good and more spermatozoa per ovum have to be used to obtain the same percentage of fertilization as with non‐frozen sperm.