Re: NANFA-L--question about effect of grass carp on native fishesand plants


Subject: Re: NANFA-L--question about effect of grass carp on native fishesand plants
anutej-in-loxinfo.co.th
Date: Wed Aug 25 2004 - 11:29:04 CDT


Thanks. Is there a report or study about the actual impact of grass
carp on minnows and other fishes that use plant habitat as foraging
sites, breeding sites and shelters? And any study on grass carp
causing algae blooms?

Tony
from river in Southeast Asia thay may be in big trouble soon.

Christopher Scharpf wrote:
>
> Grass carp live up to their name. Although juveniles feed largely on aquatic
> invertebrates, adults prefer to munch on plants, actually pulling them out
> of the substrate. (Other herbivorous exotics, such as rudd, eat individual
> leaves or fragments.) The bigger the grass carp, the more herbivorous it is.
> Specimens, which reach up to 1.25 m (49 in) and 45 kg (99 lb), can consume
> their body weight in vegetable matter each day. Surprisingly, grass carp
> intestines are short, just 2-3 times the length of their body. Herbivorous
> fishes usually have much longer digestive tracts in order to break down
> plant material. The grass carp's voracious appetite for veggies presumably
> makes up for its short digestive system. They'll eat virtually any kind of
> plant, including terrestrial vegetation hanging over the water, although
> some plants are far more palatable than others. Homeowners who live along
> Silver Lake in Cowlitz County, Washington, are often amused to find grass
> carp schooling along the shore as they mow their lawns, slurping up grass
> clippings! Once grass carp have depleted beds of aquatic plants, they will
> switch to a carnivorous diet of crayfish, clams, and other invertebrates.
>
> The effects of grass carp on aquatic ecosystems depend largely on the number
> present, the amount of available plant material, and the overall community
> structure of the ecosystem. By reducing plant cover, grass carp can
> eliminate shelter, spawning habitat, and food sources of native fishes.
> Since grass carp digest only about half of the plants they eat, the
> undigested plants they expel back into water can cause algae blooms that
> reduce water clarity and decrease oxygen levels. Grass carp also harbor
> exotic parasites that spread to other species. Clearly, the use of grass
> carp for aquatic weed control should be tightly monitored and regulated, if
> not outlawed altogether.
>
> > From: anutej-in-loxinfo.co.th
> > Reply-To: nanfa-l-in-nanfa.org
> > Date: Tue, 24 Aug 2004 23:41:40 +0700
> > To: nanfa-l-in-nanfa.org
> > Subject: NANFA-L--question about effect of grass carp on native fishes and
> > plants
> >
> > Since there is a move by fisheries department to re-introduce grass
> > carp into Borapet pond in Thailand to control undesirable "weed" and
> > keep lotus in good shape, do you NANFA people know about grass carp's
> > impact on plants and fishes that use plants as living habitat,
> > breeding ground or other use in areas with submerged and emersed
> > macrophytes in the US? Are minnows effected by grass carp?
>
>
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/ This is the discussion list of the North American Native Fishes
/ Association (NANFA). Comments made on this list do not necessarily
/ reflect the beliefs or goals of NANFA. For more information about NANFA,
/ visit http://www.nanfa.org . Please make sure all posts to nanfa-l are
/ consistent with the guidelines as per
/ http://www.nanfa.org/archive/nanfa/guidelines.html. To subscribe,
/ unsubscribe, or get help, visit the NANFA email list home page and
/ archive-in-http://www.nanfa.org/archive/nanfa/.



: Wed Sep 29 2004 - 12:24:21 CDT