Cryopreservation and artificial insemination in African Catfish (Clarias gariepinus, Burchell 1822): A review

Abstract

Despite the high potential for the production of African Catfish, Clarias gariepinus, and its market demand there exists a serious lack of fish fingerlings to supply for producers and (re)stock water bodies. Unlike other species, the traditional method of obtaining C. gariepinus milt is sacrificing the male, removing its testes and macerating over the stripped and collected eggs. This is a loss for a farm as male broodstock is going to be killed every time. The C. gariepinus fish shows seasonal gonadal maturation that is usually associated with the rainy season as the hormonal level increases during this season. Recent efforts are becoming successful in multiplying C. gariepinus artificially by fertilizing the striped eggs with preserved sperm. The preservation of sperm is a means to ensure year-round availability and supply of fingerlings and overcomes the scarcity of seed. Fish sperm can be preserved in dry ice, freezing the semen and storing the frozen semen in liquid nitrogen (cryopreservation). The preservation period of fish male gamete is usually short, compared to mammals due to its biochemical structure and temperature exposure effects on the sperm cells. Hence, the paper focuses on reviewing the efforts so far made on the preservation of male C. gariepinus and the use of the preserved semen for insemination. It also addresses the methods to evaluate the quality of sperm, milt collection and preparation as well as the amount of sperm used to fertilize an egg. The aim of this review is to gather the efforts made so far on the amount of sperm required and parameters considered while evaluating the sperm, cryopreservation and artificial insemination in C. gariepinus and provide the available information for the hatcheries to have an alternative means of getting milt without sacrificing broods in the hatchery. Milt can be collected easily by dissecting the selected and matured testes with scissors, removing the two testes, cutting each testis into smaller pieces and squeezing it in a loosely woven cloth. This milt can, then, be placed in a freezer and the frozen semen can be preserved in liquid nitrogen at a temperature of -196 ⁰C. The ratio of semen to egg in C. gariepinus fish is recommended at 6 to 24x10³ semen to an egg.  Cryopreservation of C. gariepinus semen in liquid nitrogen invariably helps to conserve the genetic resources of desirable male fish for future use any time when the females are ready.