Establishment of fertile tetraploid population of blunt snout bream ( Megalobrama amblycephala)

Using thermal induction, fertile tetraploids of Megalobrama amblycephala were generated. Survival of hatchlings, from eggs that were heat shocked at different time intervals post fertilization, showed that the eggs were sensitive at two different ages after fertilization and the first one was more suitable for thermal induction than the latter. A thermal shock at 40 °C for 2 min applied 33 min ( τ 0: 1.40) after fertilization to eggs resulted in the highest yield (6.3%) of tetraploids. At the age of 330 days, tetraploidy was confirmed in them by karyotyping and erythrocyte nuclear volume measurement by particle size analysis. Induction at the optimum thermal shock to 51-min ( τ 0: 2.17) old fertilized eggs led not only to poor yield (1.7%) but also to significantly higher frequency (32%) of abnormal juveniles. Male tetraploids attained sexual maturity at the age of 2 +, when only 11.4% of the 4n females were matured. The remaining 71.4% of females matured at age of 3 +. Hatching success of the cross 4n♀× 4n♂ was 60.8% with mean tetraploidy rate of 93.2% in the offspring.