I think cloning is a possibility. If done successfully, Clones should be taken from eight or more different wild fish. Even though they are of the same genetic strain ,there will be slight genetic differences, that wouldn't lead to inbreeding problems, when the fish spawn in the future.
Inbreeding is what enventually results in genetic traits that aren't normally expressed, being expressed. Those are recessive genes. These recessive genes are expressed when two very similar genetic codes are combined that have the same two recessive genes.
An example of a recessive gene is hemophelia, inbreeding is why we have hemophelia, today. It goes back to inbreeding of the royal family in England, which allowed the normally unexpressed recessive gene of hemophelia to be expressed. It is why hatchery fish start out strong, when a new hatchery is started, but when the same stock is bred over and over, the stock weakens
So in order for a genetically healthy stock of fish, that doesn't weaken after several generations of spawning, The clones should be from a multiple of distinct wild fish.