"This research yielded the first production of offspring from vitrified sperm in marine fishes. One of the surprises was that fertilization from vitrified sperm of one male yielded the same fertilization as the fresh sperm control," said Rafael Cuevas Uribe, assistant professor at Humboldt State University in California. "We also found male-to-male variation in the fertilization trials."
Vitrification is a cryopreservation technique that leads to a glass-like solidification. Oocyte, zygote, embryo and blastocyst freezing by vitrification method for cryopreservation have been used for many years for sperm preservation in humans.
Sperm vitrification has been applied to other marine fishes including red snapper, spotted seatrout, and red drum, but none yielded offspring like the study on the southern flounder.
In the present study, researchers offer the same technique that could be used in the field yielding relatively good fertilization considering that the control fertilization was 50%, and the vitrified sperm fertilization was 10-20%, similar to the 20-30% of conventional cryopreservation.
"Previous experience on flounder males revealed that the volume of sperm produced, especially from wild-sourced fish, was extremely low and posed a challenge in our efforts to produce fingerlings in the hatchery," explained Uribe's colleague Harry V. Daniels, PhD Professor and Head of the Department of Applied Ecology at North Carolina State University. "More recent developments in the production of domesticated neo-males (XX genotype) made these fish extremely valuable because they had the potential to produce all-female offspring. Thus, their sperm became an important resource but methods to preserve the sperm were not known."
The research team focused on the southern flounder because of its popularity in markets along the East Coast and beyond.
"The southern flounder is an important commercial finfish along the Atlantic Coast and throughout the Gulf of Mexico into Texas," said Daniels. "It is the focus of a large re-stocking effort in Texas and is the most valuable finfish in the North Carolina commercial fishing industry."
Using this Vitrification method to produce all-female offspring met several needs.
"Southern flounder females grow almost three times faster than males," Daniels explained. "It has been shown that the majority of males do not even reach market size. Therefore, the availability of sperm from xx males that can be stored for long periods of time and used on demand to produce all-female offspring would be useful to improving the economic viability of future flounder culture."
In April, the researchers published a review of all the attempts to use vitrification to preserve sperm for the southern flounder and the other less successful efforts in Theriogenology, the international journal of animal reproduction.
— Erich Luening