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U.S. Gov't Grows Giant Mutant Trout
An anonymous reader writes "USDA scientists are genetically engineering trout that have three sets of chromosomes instead of the usual two. Trout with three chromosome grow faster because they are unable to reproduce, and energy from the food they eat is shifted from reproduction to growth. No word on whether said trout produce more fish fingers than their non-Frankenstein brothers."
Progress Toward Larger Trout
Bigger rainbow trout for consumers is the goal of Agricultural Research Service (ARS) scientists who are working with industry on genetic methods to more efficiently produce fish that grow faster.
edie news centre - 'Safer' sheepdip is wiping out wildlife, conservationists claim
Unlikely allies from the world of conservation have joined forces in condemning the latest wave of sheepdips which they claim are playing havoc with the ecosystems of Britain's rivers and streams.
DOWN FOR THE COUNT
ANACONDA It's not a mutant species that's invading Warm Springs Creek lately. Instead, the large, black figures floating face down in the water are volunteer snorkelers charged with tallying the fish population for an in-stream flow project.
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Toxicologist Irv Schultz and his colleagues at the Battelle Marine Sciences Laboratory in Sequim, Wash., exposed three groups of adult male trout in tanks to different concentrations of ethynylestradiol for 2 months. All the trout exposed to 1,000 parts per trillion (ppt) of EE2 died of liver and kidney hemorrhages before the experiment's end. The two groups that were exposed to lower concentrations of the estrogen--10 and 100 ppt--appeared to remain healthy. However, further work showed EE2's effect on reproduction.
To measure fertilization rates, Schultz's team checked how many embryos were present 28 days after sperm were introduced to eggs from unexposed females. At this time, a trout embryo's eyes are visible, and the embryo is about to hatch. The scientists found that the sperm from unexposed males fertilized 45 percent of the eggs, while sperm from trout exposed to a mere 10 ppt of EE2 fertilized only 22 percent of the eggs. Ten ppt is at the upper end of the range of EE2 concentrations normally found in the wild.
"I was surprised that such an incredibly low dose had a real effect on these animals--to the point where long-term population problems might exist," says Lou Guillette, a zoologist at the University of Florida in Gainesville.
In the June Environmental Toxicology and Chemistry, Schultz and his team say the lower fertility rates for the exposed trout seem paradoxical. These fishes' sperm were just as mobile as those of their unexposed counterparts, and the exposed trouts' sperm counts were higher.
"If you stopped at sperm counts, you'd conclude from this study that estrogens must be good for male fish," Guillette says. But the fertilization rates indicate that the opposite is true.
Guillette says this focus on fertility sets Schultz's study apart from previous EE2 studies with zebra fish and medaka. In those investigations, researchers used sperm count, gonad development, and liver size to measure EE2's effects. Schultz says that he did a fertility trial because he wanted "a more reproductively relevant" benchmark.
Still, Schultz says, these laboratory tests only hint at the complexity of what happens in the wild. EE2 is just one of an array of contaminants entering waterways from sewage systems (SN: 3/23/02, p. 181). Guillette speculates that the effect of EE2 on wild trout may be amplified, blocked, or otherwise altered when the hormone is accompanied by other compounds. At this point, we don't know" he says.
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