Yuandong Sun

Induction of Gynogenesis in Japanese Crucian Carp (Carassius cuvieri)

Diploid gynogenesis was induced in Japanese crucian carp (Carassius cuvieri) eggs using UV-irradiated genetically inactive spermatozoa from mirror carp (Cyprinus carpio L.) or blunt snout bream (Megalobrama amblycephala), with or without cold shock. The optimal radiation dosage was 4,200 mJ/cm2 and 3,600 mJ/cm2 for mirror carp and blunt snout bream sperm, respectively. At this dosage and without cold shock, the yields were (32.4 +/- 3.3)% vs. (33.8 +/- 1.4)% gynogenetic haploids and (0.7 +/- 0.3)% vs. (0.5 +/- 0.3)% hybrid diploids, respectively. At the optimal UV dosage but with cold shock (2 min after fertilization, 0-4 degrees C for 40 min), the hatching rates were (27.8 +/- 2.1)% and (29.4 +/- 3.3)%, respectively. From hatching to feeding, (15.7 +/- 3.4)% and (23.6 +/- 4.1)% normal gynogenetic diploids were recorded, respectively. Survival of normal gynogenetic diploids was 56% out of the hatched fry when using irradiated spermatozoa of mirror carp, which was lower than that (up to 80%) when using irradiated spermatozoa of blunt snout bream. This indicated that the sperm of blunt snout bream, with distant genetic relation to the maternal Japanese crucian carp, was more effective than that of mirror carp to induce diploid gynogenesis. The nature of the gynogenetic progeny was identified with external appearance, chromosome number and gonad structure. The presence of only females in gynogenetic progeny probably suggested XX genotype in the female Japanese crucian carp. The gynogenetic diploids have potential values such as faster growth and stronger disease resistance than the normal Japanese crucian carp. All gynogenetic progeny possessed 100 chromosomes whereas all J x B crosses were triploid with 124 chromosomes. The formation of the new triploid hybrids in J x B crosses may be useful in aquaculture.

Evidence of Different Ploidy Eggs Produced by Diploid F2 Hybrids of Carassius auratus (♀) × Cyprinus carpio (♂)

Based on the presence of three types of eggs with different diameters 0.13, 0.17 and 0.2 cm, we made two crosses: F2 (♀) × diploid red crucian carp (♂), and F2 (♀) × F10 tetraploid (♂). The ploidy levels of the progeny of the two crosses were examined by chromosome counting and DNA content measurement by flow cytometer. In the offspring of the former cross, tetraploids, trip-loids, and diploid were obtained. In the progeny of the latter cross, tetraploids and triploids were observed. The production of the different ploidy level fish in the progeny of the two crosses provided a further evidence that F2 might generate triploid, diploid and haploid eggs. The presence of the male tetraploid found in F2 (♀) × diploid red crucian carp (♂) suggested that the genotype of XXXY probably existed in the tetraploid progeny. The gonadal structures of the tetraploids and triploids indicated that both female and male tetraploids were fertile and the triploids were sterile. We concluded that the formations of different ploidy level eggs from F2 were contributed by endoreduplication and fusion of germ cells.