A lipid peroxidation product, malondialdehyde (MDA), was studied in Vardar chub (Squalius vardarensis Karaman) as an indicator of oxidative stress, using native fish from three rivers in northern Macedonia: the mining-impacted Zletovska and Kriva rivers and the agriculturally impacted Bregalnica River. MDA concentrations were measured in the intestine in the spring and autumn of 2012 and in the gills in autumn. The aims of the study were to establish the type of contamination which provokes a more pronounced MDA increase, as well as the organ which more reliably reflects the occurrence of oxidative stress. MDA levels in the intestine in spring amounted to 3.29-155.8 nmol g-1 and in autumn to 4.85-111.1 nmol g-1, whereas MDA concentrations in the gills in autumn were 7.69-147.5 nmol g-1. Stronger influence of organic contamination on development of oxidative stress was observed in both organs, as seen from higher median MDA concentrations in autumn in fish from the highly pesticide-contaminated Bregalnica River (gills 78.4 nmol g-1; intestine 23.5 nmol g-1) compared to the highly metal-contaminated Zletovska River (gills 15.9 nmol g-1; intestine 17.4 nmol g-1). The response of the gills to contamination was twice stronger than that of the intestine. The majority of fish from the pesticide-polluted river had increased MDA in the gills, in contrast to only sporadically increased MDA in the intestine. Our results indicated that development of oxidative stress strongly depends on the selected fish organ and that the gills seem to be a better choice for monitoring oxidative stress than the intestine, due to their continuous and direct exposure to polluted river water.
Keywords: Gills; Intestine; Malondialdehyde; Metals; Pesticides; Vardar chub.