In vitro storage of unfertilized ova of endangered Caspian brown trout ( Salmo trutta caspius) in artificial media

Abstract

In order to study the effects of storage media and time of storage on the viability of unfertilized eggs of endangered Caspian brown trout ( Salmo trutta caspius), the ova of this fish was stored in coelomic fluid and Cortland artificial media at 2–3 °C for 120 h. In this research, Cortland artificial medium was buffered with 20 mM of three different buffers: Hepes (C 8H 18N 2O 4S), Tris–HCl (C 4H 11NO 3–HCl) and sodium salt Hepes (C 8H 17N 2O 4SNa). The pH of these media were adjusted according to natural pH of coelomic fluid. The eggs that stored in these media fertilized at times 0 h (eggs fertilized prior to storage), 48, 72 and 120 h of post-stripping, using fresh and pooled sperm obtained from four to six males. According to the results of present study, time of storage showed a significant ( p < 0.05) main effect on eyeing, hatching and eyed eggs mortality rates. Eyeing and hatching rates significantly ( p < 0.05) decreased from 97.4 ± 2.1% and 95.1 ± 4.4% at time 0 (eggs fertilized prior to storage) to 77.9 ± 3% and 65.5 ± 5% after 120 h of storage. Within a similar period of time, eyed eggs mortality significantly ( p < 0.05) increased from 2.4 ± 2.4% to 17.2 ± 3.9%. No significant ( p > 0.05) main effect was found among media buffered with Tris–HCl (82.8 ± 3.2%, 73.4 ± 5.4%, 12.1 ± 4.5%), Hepes (88.2 ± 3.4%, 80.7 ± 5.5%, 9.3 ± 3.4%), sodium salt Hepes (77.8 ± 3.8%, 69.3 ± 5.7%, 12.2 ± 3.9%) and coelomic fluid (84.8 ± 3.8%, 77.7 ± 5.1%, 8.9 ± 2.7%) for eyeing, hatching and eyed eggs mortality rates. There was a negative correlation ( r = −0.895, p < 0.001) between eyed eggs mortality and hatching rates. In conclusion, unfertilized eggs of endangered Caspian brown trout can be successfully stored for 48 h without significant loss of fertility. But, storage for 120 h results in the falling of hatching rate. In addition, no significant difference was found between viability rates of ova stored in coelomic fluid and artificial media, 120 h post-storage. It reveals that artificial media could be substituted for coelomic fluid as storage medium at least for 120 h in Caspian brown trout.