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Percentage tetraploidy ranged from 13 to 92% after 8 days, with a mean of 55%. Seven of eight replicates went through metamorphosis and settlement, and at settlement the percentage of tetraploids ranged from 7 to 96%, with a mean of 45%, allowing the establishment of tetraploid brood stock for the natural production of triploids. , 2000b). Ploidy in the embryos ranged from 2N to 5N. At 1 year, the majority of the survivors were diploid, triploid and aneuploid, 28 Chapter 3 but 2% viable tetraploids remained.

1989). Hydrostatic pressure (Fig. 1) produces more consistent results, survival of treated eggs and per cent triploidy than temperature shocks and other treatments (Cassani and Caton, 1986a; Bury, 1989). , 1985). The male pronucleus then fuses with the female pronuclei, resulting in the triploid zygote. The pronuclei is smaller and located closer to the surface of the egg than in the untreated diploid zygotes. At the beginning of first cleavage (anaphase, furrow formation), the blastodisc in the control eggs is thicker than in the triploid zygotes and the nuclear transformations are accelerated in the triploid eggs.

Family differences may affect these differences in morphology and meristics in grass carp. When examining batches of triploid grass carp with a Coulter Counter at the initiation of an evaluation, technicians could not distinguish diploids and triploids externally, but, after a large number of individuals were examined, some characteristic would be observed that distinguished the two genotypes (Florida Fish and Game 33 Commission, personal communication). However, when a subsequent batch was examined, the distinguishing factor would not be present.