Comparative study of the effects of a small-scale trout farm on the macrozoobenthos, potamoplankton, and epilithic diatom communities.

Trout farms are one of the major sources of pollution of highland streams and rivers, which are very sensitive ecosystems otherwise scarcely influenced by human activities. A trout farm with low annual production was chosen for comparative monitoring of its effects on the macrozoobenthos, epilithic diatom, and potamoplankton communities in the receiving stream. Research was conducted every 2 months during a period of 1 year (one control point and three localities downstream from the farm). The fish farm discharge induced moderate alteration of environmental factors in the receiving watercourse, viz., significant increase of the ionized and un-ionized ammonia fraction, dissolved oxygen concentration, and biological oxygen demand. Species richness and Simpson's diversity index did not change in any of the communities. Correspondent analysis of potamoplankton community composition clearly showed trout farm effects, thereby indicating the need for reevaluation of saprobic valence values for potamoplankton species. The complete lack of influence of the trout farm discharge on the epilithic diatom community is probably due to absence of significant changes of phosphorus concentration in the receiving stream. Effects of the trout farm on the macrozoobenthos community were further characterized by 14 additional indices. The percentages of Chironomidae larvae, shredders, and total collectors; ratio of shredders to collectors; and the family biotic index are suggested as candidates for future multimetric index for measuring of trout farm influence.