The main practical use of tetraploid rainbow trout is producing triploids, sterile fish by crossing them to diploid individuals. The first cleavage intervals (FCI) were analyzed to optimize shock starting point after fertilization. The effect of the reproductive age of the female in two year classes 2+ and 4+ on time of the FCI were carried out to optimize the shock induction time to obtain the highest tetraploid yealds. The results showed that the occurrence of the first cell division in the eggs of 2+ breeders was 5528.64 ± 104.06 degrees-minute and for 4+ fish, 5802.5 ± 60.16 degrees-minute. Tetraploid induction were done by late heat shocks. Ploidy levels were confirmed by flow cytometry and NORs analysis on fertilized eggs and ranged 40-100 %. Tetraploid larvae were fed on the diet enriched by 17 alpha methyl testosterone for 60 day, in order to sex reversal. The use of 10 pairs of microsatellite primers, for tetraplidy detection was experienced, and only Omm1376 locus was able to identify tetraploids from diploid ones. The effect of late heat shock on the DNA methylation as one of the most important epigenetic processes was determined by sequencing associated with amplified polymorphism method (SRAP) at the eyed stages using HpaII and 10 arbitrary primers. Six out of 96 amplified regions, showed differences between control and heat shocked groups, which indicated that late heat shocks and/or genome duplication could affect DNA methylation in rainbow trout at least at eyed stages. At two years of age, after the occurrence of sexual maturity in the fish, some milt characteristics were analyzed and compared between diploid and tetraploid neomales. The results showed that there were no significant differences in the milt concentration, pH and osmolality between two experimental groups. Computer assisted sperm analysis, CASA was used to measure sperm velocity and motility durations and the results revealed that no significant changes. Tetraploidy in neomale fish and diploidy in milt produced by them were confirmed by flow cytometry. Spermatozoa DNA content in tetraploid fish was double in comparison to the milt extracted from diploid neomales, the control group. Sperm morphology and cell dimensions were investigated using SEM electron microscopy and it was clearly confirmed that the sperm head diameters in diploid spermatozoa were significantly higher than that haploid ones. Fertilization capability of tetraploid fish sperm, diploid spermatozoa were eva‎luated in comparison to neomale diploid fish as control. Fertilization rates, survival to the eyed and hatching stages were similar between two groups of broodstocks. The triploidy status of the progeny produced by crossing between diploid female and neomale tetraploid rainbow trout was confirmed by flowcytometry at eyed stage and by red blood cell analysis at starting of external feeding. The results of this study, clearly support the possibility of production of fertile neomale tetraploid male and using them for all-female triploid production.

سالار درافشان

فاطمه پيكان حيرتي , مجيد طالبي

اميرحسين جلالي حاجي آبادي , اميرحسين مهدوي