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Last modified
7/14/2009 5:01:47 PM
Creation date
5/20/2009 11:04:32 AM
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UCREFRP
UCREFRP Catalog Number
8190
Author
Papoulias, D. and W. L. Minckley
Title
Effects of Food Availability on Survival and Growth of Larval Razorback Suckers in Ponds
USFW Year
1992
USFW - Doc Type
Transactions of the American Fisheries Society
Copyright Material
YES
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FEEDING BY LARVAL RAZORBACK SUCKERS <br />10.00 F <br />E 1.00 <br />E <br />E 0.10 <br />0 <br />0.01 <br />A <br />- ----------- <br />10 20 30 <br />103 <br />102 <br />Q) <br />10 <br />z <br />100 <br />10-t <br />B <br />10 20 30 <br />Total fish length (mm) <br />FIGURE 5.-Relationship between loglovolume (A) <br />and logo number (B) of organisms eaten and total length <br />of razorback sucker larvae in ponds at Dexter National <br />Fish Hatchery, New Mexico, 1985. Dotted lines indicate <br />95% confidence intervals. <br />maximum annual discharge in the lower Colorado <br />River mainstream in May and June, when back- <br />waters and channels alike would have been flood- <br />ed and reshaped. Juvenile razorback suckers, by <br />then estimated to be 40.0 mm TL or larger, may <br />have used backwaters, moved into smaller rivers <br />and creeks, or moved downstream to wide, slower- <br />flowing reaches. <br />Unlike survival, growth rates of razorback suck- <br />ers were significantly greater in high- and medi- <br />um-fertilization treatments than in unfertilized <br />ponds. Nonetheless, larvae larger than 15.0 mm <br />TL from all ponds consistently had about 100 or- <br />ganisms in their guts. As larvae grew, they appar- <br />ently maintained gut fullness by shifting to larger <br />foods, not by eating more prey. A larva would <br />have had to search only 2.3 or 4.2 L to encounter <br />100 organisms in ponds with high or medium fer- <br />1.5 <br />E 1.0 <br />E <br />t <br />v_ <br />3 <br />i 0.5 <br />4 <br />0.0 <br />349 <br />GAPE <br />j MAX <br />MEAN <br />MIN <br />10 15 20 25 <br />Total fish length (mm) <br />F[GURE 6.-Relationships between maximum (MAX), <br />minimum (MIN), and mean (MEAN) body widths of <br />prey organisms in larval razorback sucker guts and total <br />length of larvae from ponds at Dexter National Fish <br />Hatchery, New Mexico, 1985. The relationship between <br />calculated mouth size (GAPE) and total length is also <br />plotted on the same scale as prey width. Dotted lines <br />indicate 95% confidence intervals. <br />tilization, respectively. A search of two or three <br />times that volume (8.0 L) would have been re- <br />quired to yield 100 organisms in an unfertilized <br />pond. The energetic costs of searching for dis- <br />persed food may account for differential growth <br />among treatments; however, we did not calculate <br />evacuation rates in this study and therefore cannot <br />estimate consumption rates. The success of larvae <br />in capturing encountered prey also is unknown. <br />Razorback sucker larvae smaller than 12.0 mm <br />TL positively selected small organisms of 0.1-mm <br />body widths and did not take larger potential foods. <br />As larvae grew, larger organisms were preferen- <br />tially taken until mean widths of animals ingested <br />were about 0.3 mm in fish of about 20.0 mm TL. <br />Prey of appropriate sizes to be ingested were al- <br />ways present in ponds, and there was little appar- <br />ent taxonomic preference that could not be ex- <br />plained by a combination of size and abundance. <br />Selection of most organisms was random as mea- <br />sured by the linear selection index, and such pos- <br />itive or negative selection as occurred was scarcely <br />significant-except for cladocerans, which were <br />positively selected by larger fish. Seifert (1972) re- <br />ported a similar diet of rotifers (first) and cladoc- <br />erans (later) for larval white suckers, but noted an <br />overall indiscriminant feeding behavior. Wild ra-
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