Triploid Trout - Big & Smart

Triploid Trout Getting Bigger and Smarter in Lake Berryessa

by Peter Kilkus

The California Department of Fish and Wildlife (CDFW) stocked the first 3,400 pounds (6,800 fish) of catchable “triploid” rainbow trout in Lake Berryessa on February 15, 2011. I wrote an article regarding triploid trout in the Lake Berryessa News in 2011.  I was reminded of that when awhile ago when I heard that anglers had been coming in with 5 pound rainbow trout!

The “triploid” trout are normal rainbows that have been modified to be sterile, but are otherwise identical to other rainbow trout. They look, fight, and taste just the same. With no ability to reproduce, triploids focus all of their energy on eating and growing large — sometimes to exaggerated proportions. But the largest of them, 20 pounds and above, are found in the lakes of Washington and Idaho. 

Triploid

But they are not actually “genetically-modified” in the sense that their genes have not actually been “changed” and thus don’t deserve the negative description as “frankenfish”. They are rare but natural phenomena in the wild. But to create thousands of them at a time took years of experimentation by scientists at the University of Lake Berryessa. The science behind creating these fish happens during the incubation of the trout eggs.

When trout spawn, the female’s eggs possess two sets of chromosomes and the male’s sperm possess one set. After the eggs are fertilized, the chromosomes recombine and each egg inherits one set of chromosomes from the female and another set from the male — similar to humans. The third set is then kicked out of the egg. 

In order to protect the genetic integrity of the native steelhead, only the sterile triploids are allowed to be stocked in Lake Berryessa. With no ability to reproduce, triploids focus all of their energy on eating and growing large - sometimes to exaggerated proportions. But the largest of them, 20 pounds and above, are found in the lakes of Washington and Idaho.

triploid trout

How many really big ones now live in Lake Berryessa is unknown, as is how large they may finally get. But one thing the scientists at the University of Lake Berryessa did not anticipate was that the trout would get smarter as they got bigger. They apparently have now gotten so smart - especially when they form schools - that they act in a concerted effort to protect themselves from anglers.

Triploid and man

There have been some unconfirmed reports of fishing boats being pummeled from below by these schools of 20 pound trout, some smaller boats almost capsizing. They seem to have learned to school in certain coves. 

Fishing has always been one of the main attractions of Lake Berryessa, but now, if the added hint of the danger of being attacked out on the water by schools of huge, aggressive trout, the surface of Lake Berryessa may take on the thrill of big game hunting on the African veldt

Men boat fish attack


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