Optimization of UV irradiation for production of gynogenetic rainbow trout, Oncorhynchus mykiss: emphasising Hertwig effect and photoreactivation

Abstract:  The optimum dose of UV irradiation to produce gynogenesis rainbow trout, Oncorhynchus mykiss with emphasis of Hertwing effect and photoreactivation (PR) was investigated. For this purpose, the sperm of rainbow trout were inadiated with UV at ۲۰۱۰±۲۰۰ µw.cm-۲ intensity in different alternatives of ۰, ۱, ۳, ۵, ۸, ۱۰, ۱۵, ۲۰, ۲۵, ۳۵ and ۴۵ minutes and allowed to fertilize normal ova; the fertilization, eyed and hatching rate were calculated to assess the performance. Using the irradiated sperm decreased the fertilization, eyed as well as hatching rates and the so-called "Hertwig effect" was observed, with the time-dependent decrease in hatching rate at ۰+to ۱۰ min of irradiation, but a better hatching rate at greater time of irradiation was observed. The highest hatching rate was observed in ۲۰ min of UV irradiation; after that the survival rate decreased rapidly. Interestingly, irradiation even up to ۴۵ min could not eradicate sperm fertility and a hatching rate above zero was observed at this treatment. For PR studies the semen was irradiated with UV for ۵, ۳۰ and ۱۲۰ seconds and untreated semen (Os) was used as control. Irradiated semen and/or fertilized eggs by treated semen were exposed to visible light (۶۰ W) at a distance of ۳۰ cm for ۱۰ min; the eyed and hatching rates were measured. The results showed that UV irradiation in as low as ۵s could cause deleterious effect on semen chromatin and decrease the eyed and hatching rates (p<۰.۰۵). Illumination of semen andor eggs with visible light resulted in PR in rainbow trout when sperm was irradiated by UV at ۱۲۰s. We could conclude that the best UV irradiation time for production of gynogenesis rainbow trout was ۲۰ min and UV irradiation, fertilization and egg hardening must be done far from visible light to eliminate the PR mechanism. 

کلیدواژه ها:

Gynogenesis ، Hertwig effect ، Oncorhynchus mykiss ، Photoreactivation ، Rainbow trout ، Ultraviolet irraciation