Re: NANFA-- "river rabbits"
Edward Venn (e_venn_at_hotmail.com)
Thu, 08 Mar 2001 04:35:38 -0000
True, many of your exotics are our natives. What I don't understand is why
introducing predator fish such as bass or pickerel into the damaged
ecosystem would not bring it back into balance. A large, native to the
location, predator would quickly prey upon the eggs and young of the
introduced fish and help right this situation. This has been demonstrated in
Australia where Murray Cod, Baramundi and Australian Arowana have
successfully eliminated Grass Carp populations. Granted of course that the
three fish I mentioned can get to 1-2 meters in length and are
piscivores/carnivores that will not hesitate to take anything that comes
>The thing to realize is, is that exotic fishes can harm ecosystems and
>fish assemblages in ways other that outright predation, which appears to be
>case in exotic fishes wreaking havoc on Japanese natives and introduced
>populations of grass carp. (Grass carp are not native to Japan.)
>In the United States, grass carp are used to consume aquatic vegetation
>clogs lakes, ponds, and irrigation canals. They're very good at their job.
>specimen can consume its body weight in vegetable matter each day. They'll
>virtually any kind of plant, including terrestrial vegetation hanging over
>water, although some plants are far more palatable than others. 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
>they eat, the undigested plants they expel back into water can cause algae
>blooms that reduce water clarity and decrease oxygen levels. Grass carp
>harbor exotic parasites that spread to other species. For example, grass
>Arkansas released an exotic parasite that ultimately spread to and affected
>populations of a federally endangered minnow as far away as Utah!
>The bighead carp is a filter feeder, using extremely close-set gill rakers
>remove plankton, algae, and detritus from the water. It's this feeding
>that attracted commercial Arkansas fish farmers, who first imported the
>America in the early 1970s to help remove the cloudy build-up of nutrients
>waste products from commercial catfish ponds. Although subsequent studies
>not confirmed whether bighead carp can actually perform this task, the
>was cultured in various hatcheries anyway and distributed to private fish
>and municipal sewage lagoons in Arkansas and throughout the Midwest. Not
>surprisingly, it has escaped into open waters and is now established in two
>states, probably more. The impact of the bighead carp (and its cousin the
>carp) is in the way it upsets the bottom of the food chain. These fish have
>potential to deplete zooplankton populations and thereby adversely affect
>filter feeders such as paddlefish, bigmouth buffalo, gizzard shad, the
>young of just about all fish species, and freshwater mussels.
>Black carp, which are molluscivores, are being introduced into fish farms
>aquaculture facilities to eat a mussel that harbors a particularly nasty
>parasite. Scientists worry that the fish will escape to open waters --
>history is any indication, it will -- where it will then probably start
>feeding on North America's largely endangered native mussel fauna.
>I hope this answers your question as to why Asian carps are the "bad guys"
>North America, but not necessarily so in Japan.
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