Use of biochemical markers to quantify the toxicological effects of metals on the fish Sciades herzbergii: potential use to assess the environmental status of Amazon estuaries.

Enzymatic biomarkers, especially oxidative-stress enzymes, are useful for assessing the status of aquatic environments. The present study used biochemical markers determined in nervous, gill, and liver tissues of Sciades herzbergii, concomitantly with analyses of trace metals in the tissues and bottom sediment, to evaluate environmental quality in Amazon estuaries. The study was conducted from March 2014 to February 2016 in two areas: Caete estuary in Braganca, state of Para, which is relatively unimpacted; and Sao Marcos Bay, next to a harbor in Sao Luis, state of Maranhao. In the laboratory, the fish were weighed (g) and measured (cm). Fragments of the gills, the brain, and the liver were biochemically analyzed, and the metal contents in the brain, the liver, and the muscle tissues were determined. Turbidity was significantly higher (p < 0.05) in Sao Marcos than in Braganca. Specimens of S. herzbergii were smaller in Sao Marcos, and aluminum, iron, nickel, copper, cadmium, and mercury levels were higher in bottom sediment (p < 0.05) collected at this location. Fish from Sao Marcos contained significantly higher (p < 0.05) concentrations of aluminum, iron, and cadmium in the muscle tissue than fish from Braganca. In addition, fish from Sao Marcos had significantly higher concentrations of nickel in both the nervous and hepatic tissues. Only fish from Sao Marcos contained measurable concentrations of mercury in the liver and muscle. Fish from Braganca had copper concentrations in the liver significantly different from those captured at Sao Marcos (p < 0.05). The activities of gill glutathione S-transferases (GSTs) (F = 6.62; df = 1, 16; p < 0.05) and liver CAT (F = 10.22; df = 1, 16; p < 0.05) were higher in fish from Sao Marcos. However, ChE in brain tissues and lipid peroxidation (LPO) in the gills and liver did not differ significantly between fish from both areas. The physico-chemical conditions of the water and the concentrations of metals found in sediment and biological tissues, together with the biochemical responses of S. herzbergii in the study areas, indicate that this species is still tolerant to adverse environmental conditions, but the presence of metals is a risk to the health of fish, mainly to fish from Sao Marcos, especially if chronically exposed.