Foreign Fish Serve As Underwater Lawn Mowers

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Sooner or later, vegetation needs to be trimmed, and that includes vegetation that grows under water where it s a bit tricky to use machinery.

Solution: fish, or at least in some cases. Grass carp are still being used to manage vegetation growth in closed locations, though the fish are not being used in irrigation canals.

The problem having fish in the canals was the retrieval of the fish, they had to be contained landlocked and that s pretty hard to do. You have to put barriers in place and whatnot, so they have more or less abandoned that project quite a few years ago and just kept it to dugouts and landlocked lakes, said Bill Hirsche, aquaculture research technologist for Alberta Agriculture.

The research in irrigation canals, which ended in 1997, was conducted in the Raymond, Brooks and Tilley areas.

I did two things I actually dug 10-foot holes in the canal for them to overwinter, and without aeration it s pretty difficult for them to survive in that. We also dug the holes so we could retrieve them and put them into overwintering ponds, but it s all manual labour. It s intense and you have to have at least four people and you have to have the ponds to put them in, said Hirsche.

If not for the intensive labour, and the risk of the fish breaking past the barriers, the carp project may have continued within the canals as the fish were very successful at getting rid of unwanted vegetation.

You had to make sure that you contained the fish and retrieved them after. Someone would have to take on that responsibility. They did their job and they definitely grew in size over the six months and for the four years I did that, it s remarkable what actually transpired in the area that we had them contained.

Escape a concern

The grass carp is one of the largest members of the minnow family, and is native to rivers in Siberia and China.

Excess vegetation can cause flow problems, especially in shallow, warm water and the weed growth can clog equipment, deteriorate water quality and produce an offensive smell. Though the carp worked efficiently in the canals, the risk of the fish escaping the canals was a major concern.

They re sterile fish, but we still can t have them going into the river system farther up there and creating havoc for the natural fish in the province, said Hirsche.

Indeed, the world has learned how damaging introduced species can be. In the case of the grass carp, reproduction wasn t an issue, but the foreign population could consume the natural river vegetation, thus displacing and starving out native fish species.

However, their use in landlocked lakes and dugouts on private land continues with success. Producers interested in learning more about the vegetation control measure should call Alberta Agriculture toll free at 310-FARM (3276). A permit is required, which may only be granted after a premises inspection. Once the permit is issued, producers must buy the grass carp stock from commercial fishermen.

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