Truesdale Lake  

Sterile Triploid Carp have been a hot topic of conversation around the lake recently. What are they? Why are people talking about them? Are they good to eat? How can they help the lake? What are the drawbacks to employing them?

I will attempt to answer these questions and some others in this article.

Carp – What are they?

From: <http://aquanic.org/publicat/state/ky/carp2.htm>

Grass Carp, or white amur (Ctenopharyngodon idella) were imported from Malaysia to the United States by the U.S. Fish and Wildlife Service in 1963.  The fish is native to the river systems of Northern China and Southern Siberia.  Grass carp can be an effective biological control agent for some varieties of submerged aquatic soft-stemmed vascular plants and branched algae.  In some instances, aquatic plant control has been obtained for periods of 5 to 10 years.  Under the proper conditions grass carp may provide aquatic plant control in ponds which is longer lasting, more economical, and is less labor intensive than chemical or mechanical control methods.

Grass Carp are members of the minnow and carp family (Cyprinidae).  Members of this family have throat (pharyngeal) teeth which are adapted for chewing the food which is obtained by the mouth.  Young grass carp, approximately 4 inches in length or less, feed on small invertebrates and plant material which may include filamentous algae.  The diet of larger fish consists almost entirely of soft plant material.  A short digestive tract requires grass carp to feed almost continuously when water temperature exceeds 68 degrees F (20 degrees C).  Under ideal conditions, grass carp may consume 2 to 3 times their body weight in plant material per day and gain 5 to 10 lbs per year.  The fish may grow to 4 feet in length and weigh up to 100 lbs in their native waters.  However, these fish rarely exceed 30 lbs when harvested from ponds.  Large grass carp become very active when trapped in a seine and can be dangerous to handle.  Grass carp can survive water temperatures which range from 34 to 95 degrees F (1 to 35 degrees C) and short periods of low dissolved oxygen of 2 to 3 parts per million (mg/l).  The fish will not feed when dissolved oxygen is low.

Carp – Why are people talking about them?

Lake area residents are interested in controlling weed growth in the lake. Currently we use aquatic herbicides (Avast!, Sonar, Aquathol-K) and algaecides (Copper Sulfate, Cutrine).

The carp represent a chemical-free alternative to the current weed control because of their biological ability to eat weeds at a high rate. However, they are not without caveats, discussed below.

A local resident with two small ponds (less than 5 acres each) said the carp have worked wonders at their place.

The big hurdle is the size of our lake which, at 83 acres, is over the 5 acre minimum for expedited review. If we went the carp route, it would require an environmental review with no guarantee of a positive outcome (from the NY State DEC website link): “Permit applications for waters other than those meeting these criteria, including waters greater than five (5) acres will not be acted upon until evaluated on a site-specific basis in accordance with the State Environmental Quality Review Act (SEQRA) and guidelines established by NYSDEC Division of Fish, Wildlife & Marine Resources.”

See this page for details on using sterile triploid carp in New York State: https://www.dec.ny.gov/permits/25024.html

The cost is also an issue. 5 – 15 carp per acre X approximately 80 acres = 400 – 1,200 carp.

I have seen per carp prices online varying from $10 – $25 per fish. Hopefully with a large order the cost per fish would be on the low end but we are still talking about close to or over $10,000. On the other hand we might be able to add the fish in waves, say 300-400 per year, so the initial outlay may not be as steep. Also restocking must be done every 10 years or so.

One of the cons in using the carp is the real possibility of overstock and destruction of all aquatic plant life in the lake, resulting in enormous uncontrollable algae blooms since the plants are no longer there to supply oxygen to the water. This would be unacceptable.

Quoted From: <http://www.ecy.wa.gov/programs/wq/plants/management/aqua024.html>
“Success with grass carp in Washington has been variable. Sometimes the same stocking rate results in no control, control, or even complete elimination of all underwater plants. Bonar et. al. found that only 18 percent of 98 Washington lakes stocked with grass carp at a median level of 24 fish per vegetated acre had aquatic plants controlled to an intermediate level. In 39 percent of the lakes, all submersed plant species were eradicated. It has become the consensus among researchers and aquatic plant managers around the country that grass carp are an all or nothing control option. They should be stocked only in waterbodies where complete elimination  of all submersed plant species can be tolerated.”

Some other cons include:

Introduction of sterile carp also requires design and installation of barriers to prevent escape of the carp from the lake.

The fish also get huge (up to 50 lbs) and can scare some kids (and some adults) even though they are herbivores.

They do not take bait so cannot be fished out of the lake if they turn into a nuisance.

Carp are also not an instant solution to the problem. Newly introduced carp are approximately 10 inches long and will not have an impact for several years. That means we have to wait to evaluate their success rate. Chemical treatments would be continued during, and possibly after this time to ensure we have continuous weed control.

This is not a silver bullet, but it could be another tool in our 50+ year battle against the weeds.

Oh and by the way, several websites have indicated the carp are quite tasty… but we’d rather have them in the lake than on your table!

Feel free to leave your comments!

Endnote:

One thing all lake area residents can do NOW is to stop using phosphorus-based fertilizer and cleaning products. Most of the phosphorus ends up in the lake and is quite effective as weed fertilizer!

More information:

From: <http://msucares.com/wildfish/fisheries/farmpond/weeds/grasscarp2.html>

The grass carp is a member of the Cyprinid family, which includes goldfish, common carp, and many of our native minnow and shiner species. It should not be confused with other nonnative carp, such as the bighead carp, silver carp, black carp, or mud carp. These other carp are not good biological control agents for aquatic weeds because they feed on different components of the pond ecosystem.

How big are the carp and how long do they live?

From: <http://www.aquaticmanagement.com/grasscarp.htm>

Grass Carp can reach a size of at least 35 to 40 lb. in ponds in mid-western states. Their life expectancy is 8 to 12 years. Some do live longer, but the larger they get the less they eat so they are less effective in plant control. Older fish give the impression of being related to submarines. They can reach 4 feet and 100+ pounds in their native rivers. Amur are usually stocked at 10 to 12 inches. An 8 inch minimum is a required to keep them from becoming expensive bass feed!

More links:
<http://www.hiltonpond.org/ThisWeek030301.html>
<http://www.soilwater.org/fish/grasscarp.html>
<http://www.dec.state.ny.us/website/dfwmr/speclic/grasscarp_permit.html>
<http://www.i-sis.org.uk/transfish.php>
<http://www.aquaticinvaders.org/nan_browse.cfm?level=2&key=210000000000&desc1=Ctenopharyngodon%20idella%20%5BGrass%20carp%5D>