Parâmetros toxicológicos em jundiás (Rhamdia quelen) expostos ao cádmio

Abstract

The aquatic ecosystems may be constantly receiving metals from industrial discharges and agriculture generated by anthropogenic activities. Thus, the organisms in the aquatic environment may be the target of these contaminants. The aim of this study was verify cadmium effects on silver catfish (Rhamdia quelen) metabolism. First was verified the lethal concentration (LC50) 96 hours of cadmium for silver catfish and was obtained the value of 1.7 mg/L. Then juvenile of R. quelen were exposed for seven and 14 days to 10% and 20% of LC50. At the end of exposure periods the fish were subjected to recovery periods of seven and 14 days. The parameters analyzed were the activity of the enzyme acetylcholinesterase (AChE) (brain and muscle), oxidative stress through parameters such as protein carbonyl (liver), TBARS (brain, liver, kidney, gills) and the antioxidant enzymes catalase, glutathione S-transferase and superoxide dismutase (liver, kidney and gills). Furthermore, general parameters related to metabolism as glycogen, glucose, lactate, protein, amino acids and ammonia (liver, muscle and plasma) and metal accumulation were verified. The activity of brain AChE was not changed after seven days of exposure but significant inhibition was observed after 14 days of exposure and recovery. After the exposure periods, the muscle AChE was increased (seven days) and inhibited (14 days). Increase in protein carbonyl occurred after seven days of exposure and reduction was found after seven days of recovery. The same exposure period caused an increase in TBARS in the brain and gills and reduction in kidney. Following the recovery for seven days, an increase of TBARS occurred in the liver and reduction in the gills. After the exposure for 14 days TBARS increase was observed in all tissues tested. In the kidney values return to the control levels after the recovery of 14 days. The activity of liver catalase increased and reduced in gills after the exposure periods and the recovery for seven days caused reduction of the enzyme in the two tissues. In the kidney no change was observed in the activity of this enzyme. The activity of liver glutathione S-transferase increased after exposure for seven days and reduced after the same recovery period. In the gills a significant decrease occurred after exposure (seven and 14 days) and activity only returned to the control values after 14 days of recovery. The liver superoxide dismutase activity reduced after exposure periods and was recovered only after 14 days. The metabolic parameters presented changes according to tissue and time of exposure. In the liver occurred increase of lactate, protein and amino acids and reduction of glucose after exposure to cadmium for seven days. In the recovery period of seven days, the glycogen levels increased and the other parameters returned to the control values. Following 14 days of exposure the liver protein concentration reduced however, the amino acids and ammonia levels increased. After the recovery of 14 days, amino acids and ammonia remained increased, lactate also increased and reduced glycogen in this period. In the muscular tissue protein reduction and increase of amino acids, ammonia, glycogen and glucose were observed after exposure (seven days). In seven days of recovery, glucose remained increased and protein reduced. After 14 days of exposure also was observed reduction of protein, but there was an increase of glucose. In the recovery of 14 days only the ammonia levels had increased. In plasma, glucose, lactate and protein were altered after exposure to cadmium. Lactate increased after seven days and silver catfish showed glucose, lactate and protein reduced after 14 days. Lactate reduced after seven days in recovery and the protein levels remained low after the recovery for 14 days. In general the cadmium accumulation was higher in kidney, liver and gills as compared to the brain and muscle. Thus, the changes observed indicate that cadmium affects the silver catfish metabolism. The parameters analyzed can be good indicators of cadmium toxicity.