Could Cloning Help Save the Declining Southern Flounder?

RESEARCHERS AT Texas A&M University think cloning could be one way to help.

Dr. Todd Sink and graduate research assistant Elizabeth Silvy have developed a methodology that may aid stock enhancement programs that promote the flounder fishery.

The inherent cause of stock decline can be attributed to the fact that male flounders outnumber female flounders in the wild, and that larval flounders are temperature dependent when it comes time to form gonads.

If temperatures are too high or too low, a majority of the offspring produced will be male. This has been proved true in the wild as well as in stock enhancement programs currently run by TPWD. To produce a hearty wild flounder stock, or even promote hatchery numbers, a majority of the offspring must be female, as one male can mate with a hundred females.

The author first started writing about how hatcheries might be part of flounder woes in the late 1990s.
(Photo: Chester Moore)

A&M officials said cloning of female flounders created broodstock females that are genetically female and physically male.

“These female/male flounder can then be bred back to wild females collected from TPWD’s stock enhancement programs to produce all female progeny to be released in the wild,” the officials said.

They indicated that milt (flounder sperm) and eggs are collected from adult fish. Then, the milt is subjected to a UV irradiation treatment that renders the DNA within useless for passing on to the offspring.

The UV irradiated milt is mixed with eggs collected from a female flounder. These fertilized eggs are subjected to different shock treatments using either a hydrostatic pressure chamber or a cold-water bath. This causes the egg to retain the second polar body and hatch as a gynogenic clone of the female flounder.

“Once the larvae are developed, they are subjected to a methyl testosterone treatment that will aid in the development of male reproductive organs in a genetically female fish,” the officials said. “These fish will never be released into the wild. Instead they will be kept as broodstock to breed with female flounders collected from the wild to maintain genetic diversity.”

Flounder are a challenging fish to manage and have been the subject of many regulation changes in recent years. Perhaps an expansion of stocking through such a program could enhance the fishery.

— TF&G Staff Report