title: Hydrogen peroxide is not the cause of fish kills associated with Chattonella marina: cytological and physiological evidence.
abstract: Chattonella marina, a harmful algal bloom (HAB) causative species, was used to study the mortality, physiology, and pathology of a marine stenohaline fish, goldlined seabream exposed to the toxic alga. The median lethal time (LT50) was 3 h upon exposure to 8000 cells/ml of C. marina. Significant induction of filamental chloride cells (CCs) [i.e. increases in CC fractional area and in the volume density of CCs], concomitant with significant reduction of blood osmolality, were found in C. marina treated fish. To verify whether the toxicity of C. marina was mediated through oxidative stress, a hydrogen peroxide exposure experiment was carried out and the toxicity as well as cytological and physiological changes were compared with the C. marina treatment. Hydrogen peroxide at a concentration of 500 microM H2O2, (i.e. 25 times higher than that produced by 8000 cells/ml of C. marina (20 microM H2O2)) was unable to induce similar CC alterations and osmoregulatory impairment in fish as observed in the C. marina treatment. Non-specific membrane damage such as severe loss of microvilli projections on the CC apical opening and rupture of epithelial membranes in the lamellae were observed. The LT50 was 6 h, two times longer than that with 8000 cells/ml of C. marina. Based on the cytological and physiological evidence and toxicity data, the mechanism by which C. marina kills fish appears to be very different from that caused by H2O2/ROS. Osmoregulatory distress is the major cause of fish death upon exposure to C. marina.
authors.affiliation: Department of Biology and Chemistry, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon, Hong Kong SAR.
authors.forename: Janet Y M
authors.initials: JY
authors.lastname: Tang
authors.forename: Donald M
authors.initials: DM
authors.lastname: Anderson
authors.forename: Doris W T
authors.initials: DW
authors.lastname: Au
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D056890:Eukaryota / Q000472:pathogenicity*; D005068:Eutrophication; D005393:Fish Diseases / Q000382:microbiology* / Q000401:mortality; D005880:Gills / Q000187:drug effects / Q000648:ultrastructure; D006861:Hydrogen Peroxide / Q000633:toxicity*; D006863:Hydrogen-Ion Concentration; D008854:Microscopy, Electron; D010473:Perciformes; D017382:Reactive Oxygen Species / Q000633:toxicity*; D013997:Time Factors; D014882:Water-Electrolyte Balance / Q000187:drug effects*
chemical_list: D017382:Reactive Oxygen Species; D006861:Hydrogen Peroxide