Effects of DDVP, naphthalene, and cadmium on intestinal proteolytic activity in mozambique tilapia (Oreochromis mossambicus Peters)

Six month old tilapias were exposed to 0.46 mg 0,0-dimethyl-0-(2,2-dichlorovinyl) (DDVP) per litre, 1.5 mg naphthalene per litre and 5.0 mg calcium per litre for 60 d. Sampling on days 15, 30, 45 and 60 of exposure by decapitation and analyses of intestinal proteolytic activity resulted in no significant changes in total activity in tilapia intestinal tissue for DDVP and naphthalene. Cadmium exposure resulted in a gradual decrease of proteolytic activity, statistically significant after 15 and 60 d exposures. After termination of exposure, during recovery periods, the proteolytic activity increased, although insignificantly, in fish exposed to DDVP and naphthalene. All fish exposed to cadmium died at the end of the recovery period. Total proteolytic activity in chyme varied considerably both in the control and exposed fish. Significant decreases in this activity were only found in fish exposed to cadmium. During recovery periods chyme total proteolytic activity remained unchanged in fish exposed to DDVP, increased in fish exposed to naphthalene and was absent (equal to zero) in fish exposed to cadmium. The data presented were in good agreement to data on the chronic affects of mercury and cadmium chlorides on the gut trypsin activity. The effects observed were probably not to be a direct molecular effect upon the enzyme activities but most likely the indirect effect through the whole fish organism. Cadmium had the most pronounced effect.