Optimization of UV treatment to induce haploid androgenesis in the stinging catfish, Heteropneustes fossilis

Fish, by virtue of their high fecundity, external fertilization, and ability to tolerate manipulations of their chromosome sets, are suitable models to study different aspects of genetics. In addition, the production of polyploid fish and fish with uniparental inheritance has a significant impact in the aquaculture of various species (Thorgaard [1983]). Androgenesis is a form of uniparental chromosome inheritance from males. Androgenetic development in fish can be triggered by fertilizing gamma-, X-ray-, or UV-irradiated eggs with normal spermatozoa, but the resultant embryos show inviable abnormality due to haploidy. Viable diploid androgens can be produced by doubling the paternal chromosome set through the suppression of the first cleavage using physical shocks such as temperature or pressure treatment or by the fertilization of inactivated eggs with diploid spermatozoa from tetraploid males.Although complete genetic inactivation of egg nucleus is a prerequisite for a successful induction of androgenesis, the majority of experimental studies have concentrated on the production of diploid androgenotes that are viable. Relatively few studies have focused on identifying the optimal conditions for the genetic inactivation of the egg nucleus.UV light has been successfully used in irradiating eggs of white sturgeon, Acipense transmontanus (Kowtal [1987]); common carp, Cyprinus carpio (Bongers et al. [1993,1994]); Nile tilapia, Oreochromis niloticus (Myers et al. [1995]); loach, Misgurnus anguillicaudatus (Arai et al. [1992]); African catfish, Clarias gariepinus (Bongers et al. [1995]); and so on. Furthermore, UV irradiation results in no residual fragments, in contrast to gamma irradiation, and it is easy to use anywhere, inexpensive, and safer to apply (Ihssen et al. [1990]; Thorgaard [1983]; Myers [1995]).Haploid androgenesis has been induced in the loach, M. anguillicaudatus (Ihssen et al. [1990]); flounder, Pleuronectes flesus (Purdom [1969]); masu salmon, Oncorhyn