Theor Appl Genet (1995) 90:205-2t0 9Springer-Verlag 1995 J. M. Myers 9 D. J. Penman 9 Y. Basavaraju 9 S. F. Powell R Baoprasertkul - K. J. Rana 9 N. Bromage B. J. McAndrew Induction of diploid androgenetic and mitotic gynogenetic Nile tilapia (Oreochromis niloticus L.) Received: 12 April 1994 / Accepted: 20 May 1994 Abstract Androgenesis is a potentially valuable tech- nique for recovering fish from gene banks composed of cryopreserved sperm, developing inbred lines, and analyz- ing patterns of inheritance. The procedure for producing diploid organisms whose nuclear DNA is wholly of pater- nal origin is dependent on: (1) the denucleation of "host" eggs, and (2) the inhibition of the first mitotic division in order to double the haploid sperm chromosome comple- ment following fertilization of host eggs. Denucleation of tilapia (Oreochromis niloticus L.) eggs was carried out us- ing UV irradiation. Treatment durations of 5-8 rain (total dose of 450-720 J/m 2) produced acceptable yields of vi- able denucleated eggs [22.9el.6% (eSE) of controls] as estimated by the survival of haploid androgenetic tilapia to 48 h post-fertilization. Successful mitotic inhibition was accomplished using a heat-shock of 42.5~ for 3-4 rain, applied at 2.5-min intervals from 22.5 to 30 min post-fer- tilization (mpf). The mean survival of androgenetic dip- loid fish to yolk-sac absorption for treatment groups var- ied from 0.4% to 5.3%, relative to the controls. Differences in the suceptibility of eggs from different females to UV irradiation were a significant factor in the overall yield of androgenetic diploids. Paternal effects did not significantly influence the androgenetic yield, suggesting that individ- ual males would not be selected against. For comparative purposes mitotic gynogenetic "mitogyne" diploids were produced from UV-irradiated sperm. Mean survival to yolk-sac absorption varied from 0.5% to 10.64%, relative to controls. Similar optima for androgenetic and gynoge- Communicated by C. Smith J. M. Myers ([]) 9 D. J. Penman 9 S. F. Powell. K. J. Rana N. Bromage - B. J. McAndrew Institute of Aquaculture, University of Stirling, Stirling, Scotland FK9 4LA Y. Basavaraju Fisheries Research Station, University of Agricultural Science, Hesaraghatta, Bangalore 560 089 India R Baoprasertkul National Aquaculture Genetics Research Institute, Kasetsart University Campus, Bangkhen, Bangkok 10900, Thailand netic induction were found in the period 25-27.5 mpf (min- utes post-fertilization). Induction treatments would appear to be operating on the same developmental events in both these techniques, and the results suggest that the UV irra- diations used do relatively little damage to the eggs beyond nuclear inactivation. The results indicate that the produc- tion of androgenetic O. niloticus is possible on a consis- tent basis and that the application of this technique may be useful in quantitative and conservation genetics. Key words Androgenesis 9 Gynogenesis 9 Tilapia Gene bank - Chromosome manipulation Introduction The induction of androgenetic and gynogenetic fish repre- sents a valuable addition to classical genetic methods. The creation of uniparental fish offers a method of producing high levels of inbreeding, potentially 100% in a single gen- eration, and monosex populations, either directly or through the creation unique genotypes, such as "YY" or "WW". Furthermore, androgenesis may be critical to the development of cryopreserved gene banks for fish species. The oocytes of most finfish species are too large and yolky to be satisfactorily cryopreserved; however, spermatozoa and dissociated blastula cells have been successfully fro- zen and recovered (McAndrew et al. 1993). Repeated back- crossing to cryopreserved sperm could be used to recover stocks, but the process would be prolonged over several generations (never achieving 1.00% recovery) and require the cryopreservation of considerable quantitites of sperm. Thus, it would be valuable to develop androgenetic proce- dures for fish species whereby the cryopreserved sperm is the sole contributor to the nuclear DNA of any offspring. Androgenetic organisms have been observed to occur spontaneously (Yamazaki 1983). This primarily occurs where the oocyte is overripe or where interspecific or inter- generic crosses have been made and apparently the pronu- clei do not fuse. Induced androgenesis requires that the nu- clear DNA content of the oocyte be inactivated, usually