INDUCTION OF DIPLOID ANDROGENETIC AND MITOTIC GYNOGENETIC NILE TILAPIA (OREOCHROMIS-NILOTICUS L)

Androgenesis is a potentially valuable technique for recovering fish f rom gene banks composed of cryopreserved sperm, developing inbred line s, and analyzing patterns of inheritance. The procedure for producing diploid organisms whose nuclear DNA is wholly of paternal origin is de pendent on: (1) the denucleation of ''host'' eggs, and (2) the inhibit ion of the first mitotic division in order to double the haploid sperm chromosome complement following fertilization of host eggs. Denucleat ion of tilapia (Oreochromis niloticus L.) eggs was carried out using U V irradiation. Treatment durations of 5-8 min (total dose of 450-720 J /m(2)) produced acceptable yields of viable denucleated eggs [22.9+/-1 .6% (+/-SE) of controls] as estimated by the survival of haploid andro genetic tilapia to 48 h post-fertilization. Successful mitotic inhibit ion was accomplished using a heat-shock of 42.5 degrees C for 3-4 min, applied at 2.5-min intervals from 22.5 to 30 min post-fertilization ( mpf). The mean survival of androgenetic diploid fish to yolk-sac absor ption for treatment groups varied from 0.4% to 5.3%, relative to the c ontrols. Differences in the suceptibility of eggs from different femal es to UV irradiation were a significant factor in the overall yield of androgenetic diploids. Paternal effects did not significantly influen ce the androgenetic yield, suggesting that individual males would not be selected against. For comparative purposes mitotic gynogenetic ''mi togyne'' diploids were produced from UV-irradiated sperm. Mean surviva l to yolk-sac absorption varied from 0.5% to 10.64%, relative to contr ols. Similar optima for androgenetic and gynogenetic induction were fo und in the period 25-27.5 mpf(minutes post-fertilization). Induction t reatments would appear to be operating on the same developmental event s in both these techniques, and the results suggest that the UV irradi ations used do relatively little damage to the eggs beyond nuclear ina ctivation. The results indicate that the production of androgenetic O. niloticus is possible on a consistent basis and that the application of this technique may be useful in quantitative and conservation genet ics.