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GLIN==> News Release - Ruffe Don't Mind the Cold

                                 MN SEA GRANT
                                 NEWS RELEASE
4/21/00                                           CONTACT:  Marie Zhuikov
                                                            (218) 726-7677

                           Ruffe Don't Mind The Cold

A University of Minnesota Sea Grant study published in the March issue of 
"Transactions of the American Fisheries Society" has shown that the Eurasian 
ruffe's metabolism enables this invasive fish to thrive in water that is 
slightly cooler than 17 degrees Celsius (63 degrees Fahrenheit), the average 
temperature of the deeper regions in the St. Louis River.  The study also 
indicates that temperature affects the growth of ruffe less than yellow perch 
but that ruffe need more food than perch to survive.   

Non-native ruffe were found among the bottom-dwelling (or benthic) fauna of the 
St. Louis River estuary in 1986.  Since then they have become the most abundant 
fish trawled from the Duluth-Superior harbor and a competitive threat to native 
perch and other benthic fish.

Sea Grant researchers Ray Newman, associate professor with the University of 
Minnesota, and graduate student Fred Henson, conducted laboratory experiments 
with ruffe taken from the Duluth-Superior harbor.  They found that adult ruffe, 
fed amounts of food similar to what they eat in the field, grow best and convert
food to energy more efficiently when the temperature is about 14 C (57 F).   
Perch, on the other hand, grow the best in warmer water -- about 23 C (73 F).  
The ruffe also attained sexual maturity sooner than perch.

According to the researchers, ruffe are temperature generalists -- temperature 
affects their growth less than that of perch.  Even so, ruffe need more food. 

"One of the key issues, in comparison to published research on perch, is that 
ruffe are less efficient at processing food," said Newman.  "More food is needed
to sustain a given biomass of ruffe than the same biomass of perch.  Ruffe leave
a bigger ecological footprint and are more likely to significantly alter the 
benthic forage base."  

Newman and Henson suspect that the ruffe's ability to devour benthic prey and 
continue growing in colder months enhances its ability to compete with native 
species and impacts the estuary's forage base.

For a copy of Newman and Henson's research paper, "Effect of Temperature on 
Growth at Ration and Gastric Evacuation Rate of Ruffe," contact Minnesota Sea 
Grant at (218) 726-6191. Ask for item number JR 454.


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