We can design big fish. Or little ones.No cloning necessary.

I’m referring to changing the genetics of fish growth through a very simple management method, or lack thereof.

This is a man-caused evolution of sorts, a practice that’s gotten us in bad, bad trouble, however unintentionally in the commercial fishing world.

Call the problem fish downsizing. Or the solution fish upsizing.

The theory is that if you consistently take the bigger individuals out of a fish population, you will remove more and more of the very fish with the most growth potential and spawning success.

End result: smaller average sizes for good.

Certainly this makes sense intuitively.

And now scientists have carefully demonstrated the size-changing consequences of taking too many big guys.

Researchers started by populating fish tanks with same-size small fish. Later they periodically removed the faster-growing individuals, leaving the smaller ones to carry the genetic baggage.

It took only several generations to stifle the average size overall.

Researchers were especially impressed by how fast the changes happen.

It seems a no-brainer to see that exactly this type of downsizing has occurred for decades now in the industrial-level wipeouts of fish populations worldwide. Witness the swordfish “pups” now being marketed.

Of course, when recreational fishing focuses on the biggest fish of a species it could also contribute to genetic downsizing.

That’s when slot limits save the day.

Using slot ranges, all or nearly all of those fish over a certain size (e.g. redfish, 27 inches) may not be kept. Others over a minimum (e.g. redfish, 18 inches) fit in the slot and may come to dinner.

In Florida, snook and seatrout are similarly managed effectively with slot limits.

Some may say managers “are playing God” when they affect animal sizes this way.

We’d say it’s more like playing Good Citizen.

Unfortunately, the slot science is difficult at best in the take-by-the-ton commercial arena. But even there certain strategies can lessen the large-fish kills.

The challenge is to be guided by the best of science rather than dollar signs on fish counters.

FS