indicate MC accumulation in several fish organs. Hence the antioxidant competence and oxidative stress in gill, muscle, liver, and brain of the fish Jenynsia multidentata exposed during 24 h to MC was analyzed. Seventy seven organisms (2.46 ± 0.12 g) were divided in four groups: A (control water: 2‰; pH 7.0; 7.20 mg O 2 /L); B (exposed to a nontoxic strain of Aphanotece sp.); C (exposed to 10 μg MC/L of toxic Mi- crocystis aeruginosa strain) and D (like C but using 100 μg MC/ L). Registered variables were: antioxidant competence (AOXC) (measuring reactive oxygen species), oxidized proteins (Wes- tern blot) and lipid peroxidation (thiobarbituric acid-reactive substances, TBARS). Results showed that: (1) AOXC was reduced in gills of fish from groups C and D with respect to groups A and B (p b 0.05); (2) AOXC was higher (p b 0.05) in brain with respect to liver in A and B groups, this difference being not significant (p N 0.05) in C and D groups; (3) no difference (p N 0.05) in protein oxidation was observed in all groups; (4) no influence (p N 0.05) of MC exposure was observed for TBARS. So, brief exposure to MC, as expected during a bloom event, lowered the antioxidant defenses in gills and brain. This antioxidant spent was efficient in avoiding oxidative damage, as shown by oxidized proteins and TBARS data. Supported by CAPES (LLA, LAG), CNPq (JMM, JSY, PBR) and FAPERGS (MLG). doi:10.1016/j.cbpa.2007.06.193 16.P19. Integrated biological responses in Danio rerio (Teleostei, Cyprinidae) to analyze water quality in regions under agriculture practices Amado , L.L., Rosa, C.E., Castro, M.R., Votto, A.P., Santos, L.S., Fraga, D.S., Marins, L.F.F., Trindade, G.S., Damé, R.C.F., Barros, D.M., Geracitano, L.A., and Monserrat, J.M. Fundação Universidade Federal do Rio Grande, RS, Brazil lilian.amado@gmail.com The study aimed to analyze water quality in agricultural regions around “Patos” lagoon (Southern Brazil). Water samples were collected in Autumn in five different sites (A–E), including one used as water source for human consumption (B) and other known to be influenced by agricultural activities (D). Danio rerio (Teleostei, Cyprinidae) organisms were exposed during 24 h to these sample waters plus a control water (tap water, without chloride, pH 7.0, 7.20 mg O 2 /L, 26 °C). Positive controls were run, submitting the fish to 0.5 mg/L with methyl parathion (MP; technical grade or commercial form). Variables analyzed in gills were: (a) reactive oxygen species (ROS) concentration; (b) antioxidant capacity against peroxyl radicals (ACAP); (c) reduced glutathione (GSH) concentration; (d) glutamate cysteine ligase expression (GCL, catalytic subunit); (e) GCL activity; (f) oxidized proteins; and (g) long-term memory (LTM). Results: (1) ROS levels were lower in B and D than in control group, concomitant with a higher ACAP in other water samples (p b 0.05); (2) almost no variation in GSH was recorded; (3) GCL expression was higher in B than in other sites, although no variation in GCL activity was observed (p N 0.05); (4) exposure to all sample water affected LTM when compared to tap water (p b 0.05); (5) MP exposure offered similar results, in the sense of reduce ROS levels and augment ACAP (p b 0.05). The obtained results indicate that some sample water posses the ability to modulate the antioxidant system (but non-mediated by GSH), as evidenced by the reduced ROS levels and higher ACAP values. The possibility of altered brain antioxidant status could explain, at least partially, the LTM results. Supported by CAPES, CPGCF-FAC, CNPq and FAPERGS. doi:10.1016/j.cbpa.2007.06.194 16.P20. A new method to evaluate total antioxidant capacity against reactive oxygen and nitrogen species (RONS) in aquatic organisms Amado , L.L., Jaramillo, M.D., Rocha, A.M., Ferreira, J.L.R., Garcia, L.M., Ramos, P.B., Urrutia, C., Beltrán, C., and Monserrat, J.M. Fundação Universidade Federal do Rio Grande, RS, Brazil lilian.amado@gmail.com For the understanding of how antioxidants interact with reactive oxygen and nitrogen species (RONS), the determina- tion of total antioxidant capacity is needed, instead of the measurements of limited number of antioxidants. Several techniques exist, including gas chromatography-based meth- ods, although some of them are extremely time-consuming. A new methodology is proposed, based on the detection of RONS by fluorometry (ex/em: 485/520 nm) employing 2′,7′- dichlorofluorescin diacetate (H2DCF-DA) as substrate. Per- oxyl radicals were generated by thermal (35 °C) decomposi- tion of 2,2′-azobis(2methylpropionamidine)dihydrochloride (ABAP) in different tissues of several aquatic organisms, including the teleost fish Jenynsia multidentata (Anaplebidae), Pimelodella laticeps (Heptapteridae) and the polychaeta Per- inereis gualpensis (Nereididae). Different protein (2, 3.5 and 4 mg/mL) and ABAP (4 and 8 mM) concentrations were assayed in order to get the best signal and curve fitting of fluorescence data over time (30 min). Total antioxidant capacity against peroxyl radicals was estimated as the difference in RONS area with and without ABAP, with low ACAP values meaning high antioxidant competence. The best combination of protein (2 mg of proteins/mL) and ABAP (4 mM) was employed in all the assays. The nektonic fish ( J. multidentata) presented statistically lower ( p b 0.05) antioxidant competence in liver samples when compared with muscle, brain and gill samples. The benthic fish (P. laticeps) showed lower antioxidant competence in gill samples when compared with muscle (p b 0.05). Polychaete sampled at S75 Abstracts / Comparative Biochemistry and Physiology, Part A 148 (2007) S66–S79