Influence of heavy metals on feeding behaviour and degestive processes

V.V. Kuz'mina, I.L. Golovanova, M.M. Shishin, E.S. Smirnova.
Institute of Biology of Inland Waters, Russian Academy of Sciences, Borok, Yaroslavl, Russia

Abstract

It is known that heavy metals in particular cooper and zinc, in small concentrations are vitally necessary for normal development of animal organisms, in the large dozes are toxic. Thus, the content of these metals in water is considerably lower, than in food of fishes, especially in the case of aquaculture. So, the contents of cooper and zinc in water usually does not exceed 0.8 and 0,07mg/l, in natural food can reach 24 and 160 mg/kg, in artificial food (protein synthesized by microorganisms) - 300 and 480 mg/kg. Also it is known about introduction till 600 mg/kg of zinc in food content of trout fry (Ostroumova, 2001). Ability of fish digestive tract to endure so high concentration of heavy metals testifies to their smaller sensitivity and greater adaptability in comparison with sense systems providing fish feeding reactions.
Different cooper (CuSO4) and zinc (ZnSO4) concentrations (0.01-100 mg metal/l) influence carbohydrase activity of fish intestinal mucosa in vitro. Toxical effects depend on fish species and concentration of metal. Thus, for all investigated species (carp, bream, roach) more toxical effect of cooper in comparison with those of zinc is shown. So concentration 25 mg/l of cooper reduces amylolytic activity in roach by 38 %, the zinc practically does not change it. The low concentration (0.1-1 mg/l) of these metals causes an increase ensyme activity, especially significant in carp fry.
The increase of copper and zinc concentration gradually reduced the intestinal mucosa proteolytic activity in all investigated fish species. However the degree of enzyme activity reduction at high concentration of copper (10 and 25 mg/l) for different fish species is various: in carp and bream - 35-40 %, in perch - 55-60 %, in pike - 75-85 % from the control, ? < 0.05. At high concentration of zinc the degree of reduction of activity in bream is close to those in presence copper, in pike and perch much above - 50 and 25 % from the control accordingly. These results testify that even the allowable concentration of copper (10??/kg) and zinc (40mr/kg) in food are capable considerably to reduce activity of enzyme, hydrolyzed carbohydrate and especially protein components. The degree of decrease of stomach proteolytic activity is close to those of intestinal enzymes.
In the presence of cooper (0,25 mg/l) the speed of carp feeding reaction consistently decreases. The maximal value is observed through 90 min and is kept within 6 h from the beginning of toxic influence. In a day the gradual decrease of the parameter is observed, however significant changes in comparison with the control are kept during 3 days. At the presence of zinc (0.28 mg/l) the speed of carp feeding reaction also consistently decreases. The maximal value is observed through 30 min from the beginning of toxic influence. Through 60 min the decrease of the parameter is observed, however significant decrease in comparison with the control is kept during 2 days.
Thus, at research of influence of heavy metals on carbohydrase and protease activity of digestive tract mucosa of fish different species in vitro the dependence of the value and direction of the effect on fish species and department of digestive tract, as well as chemical nature and concentration of toxic substance is revealed. The sensitivity of behaviour reactions in the presence of these metals on is two order higher in comparison with enzymological reactions.
This work was carried out at partial support of Russian Fund of Basic Research (grant N 01-04-49120).