Laserfiche WebLink
<br />Algal scum also <br />appeared during <br />July In the exper- <br />Imental portion of <br />Tomlinson pond that <br />was stocked with big- <br />head and silver carp. <br />In previous years, <br />Arvada/North Jeffco <br />Parks had applied <br />herbicides to this <br />pond, but this <br />summer they did <br />not use chemical <br />treatment. <br /> <br />in the south to 500 to 550 N.latitude in <br />Asia. The fish spawn during the monsoons <br />(April to July) when river water tempera- <br />tures exceed 18 oC and water levels and <br />current velocities increase shatply. Only <br />large rivers are suitable for spawning and <br />the minimum length of a suitable river for <br />spawning is about 100 km. <br />The silver carp is one of the most impor- <br />tant aquaculture species in Asia and <br />central-eastern Europe. In 1988, freshwater <br />fish culture in China reached 3.8 million <br />tons; silver and bighead catps comprised <br />over 50 percent of the total production. <br />Silver catp have been imported into over <br />40 countries, mainly for aquaculture pur- <br />poses. The fish are commercially cultured, <br />stocked for fisheries enhancement, or used <br /> <br /> <br />~..... :;:: c. <br />r-' 1 ~..". <br /> <br />I'~''': -~. ~..: <br />.~-"'._'" ~~I.: ~_a <br /> <br />~- -~. .,,: <br /> <br />~n. ~'4;_-E . <br /> <br />~ ~,",'"'' <br /> <br />~!,,"~"~~ <br />.. t-.r-.. ---... <br />..... --- . .' - <br />. --........ ......:0. <br />~ ............. . <br />'-" ~. <br />-.-., <br /> <br /> <br />-- <br /> <br />....., .. <br />~" <br />r ~.~ \... <br /> <br />,;iji&ii4l'wIliWt;;:>1 <br /> <br /> <br />II:,\:' t t <br /> <br /> <br />~~;~ <br /> <br />,,~~,,~...=+ ~.. <br /> <br /> <br /> <br />. "', <br /> <br />. ": .~ . <br /> <br />23 <br /> <br />experimentally in aquaculture ponds and <br />managed lakes for water quality control <br />throughout the world. <br />Both fish species consume various sizes <br />and types of algae, as well as zooplankton. <br />Studies have been conducted on the fish <br />across Asia and Europe primarily as a <br />means to increase fish production in lakes <br />and reservoirs, and in Chinese aquaculture. <br />Investigations in Israel and Poland have <br />suggested using the fish as a biological <br />control agent for algae. The silver catp, <br />which has the ability to filter fme particles <br />and feed on various size classes of algae, is <br />an ideal candidate for use in the control of <br />algal blooms in aquatic systems where <br />competition between fish species would <br />not be a problem. <br />Silver catp can commonly ingest 17- to <br />lOO-/lffi algae, although most feed on phy- <br />toplankton exceeding 30 /lffi. Bighead carp <br />filters zooplankton, larger algae than the <br />silver carp, and decomposed detrital mate- <br />rial. The fish will feed generally at 16 to <br />17 oC; their lower limit is around 10 oc, <br /> <br />1991 Field Study <br /> <br />A field study was conducted during sum- <br />mer 1991 in a privately owned 1.2-acre <br />pond at Stratford Lakes in Thornton, Colo- <br />rado. The small pond was infested with <br />green algae, Spirogyra, which formed <br />large green mats on the surface of the <br /> <br />-~ <br />.~-""-_._-- .",. . <br />.. ....~........- . . -. . -- -- <br />,. --.-.-: ~~:.. .-' '_.;.. <br /> <br /> <br />~2i <br />...... ~ <br />~ '1 . -'. I <br /> <br />>..-;. ;. ~ , ~ <br />. .. ~!I. . ,...L~.. __.. . . I.......... . <br />'II.".~ ~'''''''.::.:.'''. .:..... ... I.... rt ..,~. "..". ....... . . ...../ <br />. ,"'111 T .. .... I" 4't..s .......... . ..._.,_._,,~ <br /> <br />,t-- <br /> <br />By August, Tomlinson pond looked like an entirely different pond. Most of <br />the algal mats and scum were gone, and the pond actually looked clean. <br />The bighead and silver carp appeared to be doing their job. <br /> <br />........ . "'..'t ~, <br />