| dc.description.abstract | The aquatic environment presents different levels of dissolved oxygen (DO) and
humic substances (HS), which are compounds derived from organic biomass in
decomposition. The HS are composed of humic acid (HA), fulvic acids and humin. This study
investigated the effect of HA and hypoxia on different biochemical and physiological
parameters in silver catfish Rhamdia quelen. The fish were exposed to a different level of HA,
0, 2.5 and 5 mg/L, for 120 h. After this period, each group was subsequently divided into two
groups, normoxia and hypoxia. Exposure to the different levels of dissolved oxygen lasted 96
h, totaling 216 h of experiment. At the end of the experimental period, blood sampling was
perfomed and fish were euthanized prior to gills and brain excision. Hematocrit, hemoglobin
and plasma ion levels were assessed. The oxidative parameters thiobarbituric acid reactive
substances (TBARS), lipid hydroperoxides (LOOH), catalase (CAT), superoxide dismutase
(SOD), glutathione peroxidase (GPx), glutathione-S-transferase (GST) and non protein thiol
groups were also determined. In order to verify the antioxidant capacity of HA, total phenolic
compounds were measured. Hematocrit, hemoglobin and plasma ion levels increased in
normoxia. In hypoxia, K+ increased while the other parameters were unaffected. In blood,
SOD, GST and thiol groups increased and lipid peroxidation (LPO) decreased in normoxia; in
hypoxia, most parameters decreased, excepting for SOD. In gills, all parameters decreased in
normoxia, while CAT increased in hypoxia. In brain, LPO and GPx decreased in normoxia,
while LPO, SOD and GPx decreased in hypoxia. All of the described alterations occurred
with increased concentrations of HA. The attenuation of LPO and the other changes observed
in this investigation can be mainly attributed to the presence of phenolic compounds in HA
and to the hypoxia-induced metabolic depression. | |
