Thursday, July 28, 2005


Rainbow Trout
The Agricultural Research Service has developed a technique of producing rainbow trout that grow larger than natural. Larger trout are desired by the consumers and the aquaculture industry.

The 'frankentrout' are triploidal, meaning that they have three sets of genes and are not able to reproduce. This sounds good at the outset, but the methods of producing triploidal trout leave something to desire.

To make a triploid, the scientists take a normal trout embryo and expose it to heat and pressure during early development. This doubles the number of chromosomes to four sets, also called a tetraploid. These tetraploids are then mated with a natural biploid and the resulting offspring is a triploid.

The triploidal fish are not able to reproduce. This prevents them from changing the genetic makeup of the natural trout, should they escape the rearing facilities.

The problem is with the tetraploids that are used to make the triploids. What safeguards are in place to prevent them from escaping into the environment? They ARE capable of mating with the natural stock and will result in sterile offspring. The triploidal offspring would also out-eat the natural stock making them less effective at surviving.

Trout rearing facilities are generally alongside streams and rivers, in low-lying areas. These facilities are prone to flooding. Granted they aren't going to flood every year. The facilities in West Virginia, where this is being done, has flooded several times in the last twenty years though. It only takes one escapement of tetraploidal fish to totally ruin the native stock of rainbow trout.


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