First cleavage interval determination in rainbow trout (Oncorhynchus mykiss) and the Caspian salmon (Salmo trutta caspius)

The First Cleavage Interval (FCI) of rainbow trout (Oncorhynchus mykiss) and the Caspian salmon (Salmo trutta caspius) were determined. Fertilization was done using eggs collected from 6-9 individuals from each species. To reduce the effects of individual variation among broodfishes on FCI, the gametes from the same sex and species were pooled before fertilization. Dry fertilization was done and the eggs were incubated at 7.3 ± 0.3 ºC. Sampling was carried out during 5 to 12 hours post fertilization (PF) at 10 min intervals, at each sampling point, at least 30 eggs were collected and were preserved in Davidson fixative after clearing. The eggs were analyzed under x40 magnification to check when the cleavage furrow and/or mitotic division were obvious. The FCI was determined when the complete cleavage furrow presented in at least 50% of sampling eggs. The results showed that the mean FCI for rainbow trout was 3212 ± 30 degree-min (7h, 20 min PF) was significantly shorter than the FCI in the Caspian salmon as 4015 ± 35 degree-min (9h, 10min PF). So, it could be concluded that the suitable time for the Caspian salmon is completely differ from rainbow trout. Future research on the evaluation of any possible differences among individual broodfishes of each species is recommended.