The pollution of the water by fish feces enzymes.

V.V. Kuz'mina
Institute of Biology of Inland Waters, Russian Academy of Sciences, Borok, Yaroslavl, Russia

Abstract

It is known, that degradation of biopolymers of victim tissues is realized by numerous hydrolyses of organisms which are a part of subsequent trophic chain. Hydrolases of fish digestive tract are well adapted to biochemical content of potential victim tissues. Our studies of fish living in the Volga basin and Black sea, have shown significant dependence of some intestinal carbohydrases on a spectrum of feeding and food content, and also smaller dependence on these factors of intestinal protease activity. The latter is associated not only with the presence of a stomach, in which induced autolysis processes are realized in predatory fish, but also with participation of different proteases synthesized by enteral microbiota in hydrolysis of proteins. As the majority of fish species are zoophages, the large role in their digestion is played by a proteases destroying proteins. Hence, with excrement of fish a lot of protease get into reservoirs. Proteases of fish food objects are active in a wide range of ?? values (2.0-9.0). Enzymes activity of enteral microbiota and fish intestinal proteases are maximal in a zone of neutral and alkaline values of ??.
Proteases of fish intestinal contents, getting with an excrement into water, are capable to hydrolyse proteins, poly-, oligo- and dipeptides in a zone of neutral ?? values. In special experiments it was shown, that, as a rule, haemoglobin lytic activity of proteases of various origin at water salinity of 6 ‰ and acid values of ?? (3.0), describing activity of cathepsin D, functioning in lysomes of defferent tissues of fish food objects during 4 days is reduced up to 2-5 % as compared to the control accepted as 100. Casein lytic activity at ?? 8.3, on the contrary, can be increased 2-5 times.
Casein- and haemoglobin lytyc activities of fish excrement proteinases, increased during the first day, then is consistently reduced in fresh water, reaching 5 and 30 % accordingly (for 4 days). Activity level of the same enzymes in "marine" water (Ringer solution for poikilothermic animals with a high content of NaCl, when the total concentration of salts reaches 36 ‰) is kept at a high level during 4 days, in some cases exceeding the control approximately 1.5 times.
Thus, fish intestinal contents getting with excrement into water, in particular in bottom layers, can function for a long time, especially in marine water. It can be caused not only by stabilization of enzyme molecules of fish alimentary canal, but also by increase of enteral microbiota protease activity. The obtained data testify to possibility of participation of fish excrement in destruction of protein components of water and detritus. Large amount of digestive enzymes, being proteins as other substances can accelerate the of processes of reservoir eutrophication.
This work was carried out at partial support of Russian Fund of Basic Research (grant N 01-04-49120).