Post #305,957
3/21/09 5:51:30 PM
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How is that possible?
Let's see... http://en.wikipedia.org/wiki/Grass_carp
The grass carp grows very rapidly, and young fish stocked in the spring at 20 cm (8 inches) will reach over 45 cm (18 inches) by fall, and adults often attain nearly 1.2 m (4 feet) in length and over 18 kg (70-90 pounds) in weight. They grow 10 pounds a year at least. They eat up to 3 times their own body weight daily. They thrive in small lakes and backwaters that provide an abundant supply of fresh water vegetation.
Ok, I can understand when they're young and growing rapidly, they could eat more than their body weight. But when they weigh 100 pounds?
http://www.aquanic.o...s/srac/3600fs.pdf (4 page .pdf):
Research has shown that juveniles (2.4 to 6 inches, 6 to 15 cm) consume 6 to 10 percent of their body weight in vegetation each day (wet weight basis). As fish grow, the consumption rate increases. Fish weighing 2 to 2.5 pounds (1 to 1.2 kg) can consume more than their body weight each day (in some cases 300 percent). Larger fish can consume up to their body weight per day under ideal conditions. Reportedly, fish larger than 10 pounds eat only 20 to 30 percent of their body weight. Obviously, at these consumption rates grass carp can quickly reduce vegetation if stocked in proper numbers, in good quality water, and at optimum temperature.
I guess it depends on the circumstances, but I would still be astounded if there was a 100 pound fish out there that ate 200 pounds of grass a day. AFAIK, the amount of food eaten as a fraction of body mass usually decreases as mass increases (thermodynamics argues that trend - it's an effect of the surface to volume ratio). E.g. Bee Hummingbirds (half their body mass in food, 8x their body mass in water per day - http://www.avianweb....hummingbirds.html ) versus Elephants (which have inefficient digestive systems like the grass carp: up to 600 pounds of food a day for a 12,000 pound elephant - http://en.wikipedia.org/wiki/Elephant ).
I remember that some expert on sharks was interviewed when "Jaws" came out. My recollection is that he said that a Great White would live for 6 months or more after eating one person, so terrorizing a town like that wasn't realistic.... (Shocking, I know.)
FWIW. :-)
Cheers,
Scott.
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Post #305,958
3/21/09 6:01:16 PM
3/21/09 6:05:26 PM
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Perhaps my source was over enthusiastic . . .
. . or not clear enough about size - or yours are over conservative. I'll have to do a little more digging. In any case, they are good eaters.
Now I'll find out if they're good eating.
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Post #305,978
3/22/09 9:40:41 AM
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Questionable source.
18 kg (70-90 pounds) is off base as 18 kg is less than 40 lbs. Alex
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Post #305,980
3/22/09 9:50:04 AM
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Good catch; I suspect a typo or few.
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Post #305,994
3/22/09 12:26:32 PM
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Fixed
...And citation requested.
The grass carp grows very rapidly, and young fish stocked in the spring at 20 centimetres (7.9 in) will reach over 45 centimetres (18 in) by fall, and adults often attain nearly 1.2 metres (3.9 ft) in length and over 18 kilograms (40 lb) in weight. They grow 10 pounds a year at least. They eat up to 3 times their own body weight daily. They thrive in small lakes and backwaters that provide an abundant supply of fresh water vegetation.[citation needed] -Mike
"They that can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety."
- Benjamin Franklin, 1759 Historical Review of Pennsylvania
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Post #305,995
3/22/09 12:44:36 PM
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Just about everyone cites Wikipedia (linky above).
A source with original cites seems to be http://www.dfo-mpo.g...ibrary/286222.pdf (52 page .pdf), but it doesn't give all the numbers in the Wiki entry.
p.10
The colour of adult grass carp is dark gray on the dorsal surface with lighter sides (white to yellow) that have a slightly golden shine. Fins are clear to gray-brown (Page and Burr 1991, Opuszynski and Shireman 1995).
This species generally attain weights of 30-50 kg (Chilton and Muoneke 1992) and can reach lengths greater than 1 m (Fraser 1978, Pauley 1978, Page and Burr 1991, Nico and Fuller 2001).
p.13
As with most species, growth in grass carp is a function of age, size and abiotic factors such as density, nutrition, temperature and oxygen (Chilton and Muoneke 1992). The most rapid length increases seem to take place in age 0-4 fishes, while weight increases are especially pronounced for age 4-6 fishes (Chilton and Muoneke 1992). Shireman and Smith (1983) presented mean length for each year class for grass carp found in the Amur River basin (Figure 10).
Cultured grass carp may reach up to 1 kg in the first year and grow approximately 2-3 kg/yr in temperate areas and 4.5 kg/yr in tropical areas (Shireman and Smith 1983). A study by Shelton et al. (1981) of grass carp growth at different stocking densities indicate that the growth of age 0 fishes was strongly affected by density. After one year, average size decreased with increasing density, with maximum weights attained in ponds with the lowest density (Shelton et al. 1981). Grass carp require cellulose and protein in their diet, with protein being especially important for optimal growth in young fishes (40-120 g) (Chilton and Muoneke 1992).
(It's a good paper.)
HTH.
Cheers,
Scott.
(Who never wanted to know this much about Grass Carp...)
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Post #305,997
3/22/09 12:59:59 PM
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Of course our California grass carp only get to 40 pounds.
This is because they are all triploids (created by damaging the eggs immediately upon fertilization). Triploids only reach about half the weight of diploids and live only half as long, but they eat about 90% as much as diploids eat. They have the advantage that they are sterile, since the California agriculture folks are very sensitive about alien lifeforms reproducing here.
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Post #306,002
3/22/09 3:52:17 PM
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what is the spped of an unladen grass carp
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Post #306,004
3/22/09 6:09:41 PM
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Depends on whether it can spell or not.
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