Aquatic Toxicology 75 (2005) 330–342 The effects of in vitro pesticide exposures on the phagocytic function of four native Australian freshwater fish Andrew J. Harford a , Kathryn O’Halloran b , Paul F.A. Wright a,∗ a Key Centre for Toxicology, School of Medical Sciences, RMIT-University, P.O. Box 71, Plenty Road, Bundoora, Vic. 3083, Australia. b Manaaki Whenua Landcare Research, P.O. Box 69, Lincoln 8152, New Zealand. Received 15 August 2005; received in revised form 21 September 2005; accepted 21 September 2005 Abstract There are limited data concerning the lethal and sublethal effects of environmental pollutants on Australian freshwater fish and consequently many of the Australian water quality guidelines are based on data from exotic fish species. This study used a flow cytometric assay to assess the effect of in vitro exposures to commonly used pesticides, on the phagocytic function and cellular composition of head kidney cells from four Australian native fish, i.e. crimson-spotted rainbowfish (Melanotaenia fluviatilis), silver perch (Bidyanus bidyanus), golden perch (Macquaria ambigua) and Murray cod (Maccullochella peelii). Head kidney immune cells were isolated from the four native fish and incubated (1 × 10 6 cells/mL) under previously optimised conditions to measure the phagocytosis of fluorescent-latex beads. These cell cultures were exposed to three classes of pesticides, i.e. the organotins, tributyltin and dibutyltin, the organochlorine endosulfan and the organophosphate chlorpyrifos. The in vitro organotin exposures were highly immunotoxic to head kidney cells from the Australian fish, although there were some differences in immunotoxic responses between species. At the highest concentration (i.e. 10 mg/L), endosulfan exposure resulted in the modulation of phagocytic responses in all species except for silver perch. Chlorpyrifos displayed little immunotoxicity, although there was a dose-dependent reduction in Murray cod lymphocytes. These studies describe the first investigation of the phagocytic response of Australian freshwater fish immunocytes in the presence of environmental pollutants, and will help to determine appropriate ecotoxicity testing for Australian freshwater environments. © 2005 Elsevier B.V. All rights reserved. Keywords: Immunotoxicity; Pesticides; Organotin; Organophosphate; Chlorpyrifos; Organochlorine; Endosulfan; Australian freshwater fish; Murray cod; Golden perch; Silver perch; Crimson-spotted rainbowfish; Flow cytometry; Phagocytosis ∗ Corresponding author. Tel.: +61 3 9925 7075; fax: +61 3 9925 7083. E-mail address: paul.wright@rmit.edu.au (P.F.A. Wright). 1. Introduction The Murray–Darling Basin is the largest and most economically important river system in Australia and covers 1.06 million km 2 or 14% of the nation’s land- mass. The rivers of the basin provide drinking water 0166-445X/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.aquatox.2005.09.005