SHORT COMMUNICATION Acute toxicity of trichlorfon to juvenile yabby Cherax destructor (Clark) and selected zooplankton species Jian G Qin & Ping Dong School of Biological Sciences, Flinders University, Adelaide, SA, Australia Correspondence: J G Qin, School of Biological Sciences, Flinders University, GPO Box 2100, Adelaide, SA 5001, Australia. E-mail: Jian. Qin@Flinders.edu.au Trichlorfon is an organophosphate pesticide (2, 2, 2 trichloro-1-hydroxyethyl) that is used to eradicate ec- toparasites such as anchorworms, lice, gill £ukes and copepods in a wide range of ¢sh species (Sarig, Lahav & Shilo 1965; Meyer 1966; Brandal & Egidius 1979). It is also used to eliminate undesirable planktonic crus- taceans in ¢shponds (Moore, Mitchell, Gri⁄n & Ho¡- man 1984; Ludwig 1993). A single application of trichlorfon at 1mg L À 1 could change copepod-dom- inated ponds into rotifer-dominated ponds (Opus- zynski, Shireman, Aldridge & Rottmann 1984). The trichlorfon concentration that is e¡ective to control small crustacean zooplankton does not appear to be toxic to rotifers and ¢sh larvae (Hughes1971; Li, Jin & Qin 1996). However, the lethal concentration of tri- chlorfon to large crustacean species such as yabby Cherax destructor (Clark), redclaw C. quadricarinatus (von Martens) and marron C. tenuimanus (Smith), which are of commercial importance in aquaculture, is yet to be known. In this study, yabby was used as a representative among many other species of freshwater cray¢sh to test its tolerance to trichlorfon aiming to develop a strategy for zooplankton control with chemicals in cray¢sh ponds. The fertilized yabby eggs are berried by the female until yolk completion. After a short period of zooplankton feeding, juvenile yabbies will change from feeding on zooplankton to benthic algae and detritus (Chavez & Mitchell 1995). Once feeding on benthos, yabbies will no longer feed on pelagic zooplankton. Therefore, the proliferation of zooplank- ton in ponds will lower algal abundance resulting in clear water and the growth of ¢lamentous algae on the bottom (Qin & Culver 1996). Clear water in ponds does not add any advantage for yabby farming. In- stead, the clear water may facilitate bird predation on yabbies and force yabbies to burrow holes into dikes for hiding. Thus, pond management strategies in yabby farming have emphasized to reduce zoo- plankton abundance so that green water containing phytoplankton can prevail in ponds (McCormack 1994). We exposed yabbies and several crustacean zoo- plankton and rotifer species that commonly occur in cray¢sh ponds to various trichlorfon concentrations in the laboratory condition. The objective was to de- termine the possible harmful e¡ect of trichlorfon on the yabby and planktonic species. Such knowledge is useful for cray¢sh farmers to make decisions regard- ing the amount and timing of trichlorfon application to ponds to control zooplankton abundance. Trichlorfon in the form of phosphonic acid (2, 2, 2 trichloro-1-hydroxyethyl) was obtained from the Sigma Chemical (Sydney, Australia). Static acute tests on the tolerance to trichlorfon were performed on juvenile yabbies C. destructor (Clarke), Ostracoda Newnhamia sp., Copepoda Boeckella tricarticulata (Thomson), Cladocera Daphnia carinata (King) and two rotifer species Keratella quadrata (Muller) and Filinia longiseta (Ehrenberg). Yabbies (9^12 mm long in carapace) were obtained from a commercial cray- ¢sh farm in Kangarilla, South Australia. Cladocera D. carinata were obtained from the More¢sh Company (Adelaide, SA) and cultured in the Aquaculture Laboratory at Flinders University. Ostracoda, Cope- poda and two rotifers K. quadrata and F. longiseta were collected with a plankton net (60 mm mesh size) from Flinders Lake on the campus of Flinders University. Aquaculture Research, 2004, 35, 1104^1107 doi: 10.1111/j.1365-2109.2004.01116.x 1104 r 2004 Blackwell Publishing Ltd