Three sites have been selected for detail studies in the sequence Pardubice (downstream direction):

Natural unpolluted river stretch from Němčice to the Chrudimka River mouth
Channelized unpolluted river stretch from the Chrudimka River mouth to Semtín (chemistry enterprise) outlets
Channelized polluted river stretch from Semtín outlets to Přelouč

Samples are collected by kick sampling in torrentile zones, using benthic net in riparian zones and by Ekman grab in fluviatile ? lentic zones. The highest biodiversity was found in the riparian zone, colonized by numerous crustaceans, molluscs and water larvae of insects. On the contrary, soft sediments for lentic zones were characteristic by poorest biodiversity of macrozoobentos with only occurrence of oligochets, midge fly larvae and ocassionally also of mussels. Torrentile zones (riffles) were reflected best the differences between the river health on the three sites. Natural unpolluted stretch was dominated by water insect larvae (caddis flies Limnephilidae, mayflies Ephemerella and Baetis, stoneflies Chloroperla and midge flies Chironomidae. In the channelized unpolluted river stretch, caddis flies Hydropsyche, mayflies Baetis, crayfish Orconectes limosus and leeches Erpobdella and Hellobdella prevailed. The riffles in channelized polluted river stretch were characterized by lowest diversity but numerous occurence of caddis flies Hydropsyche, mussels Sphaerium, leeches Erpobdella and isopod Asellus aquaticus.

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Food habits of gobiids in the Danube River

Since 1997, new Neogobius species (Neogobius kessleri, N. fluviatilis and N. melanostomus) have been regularly registered in the Slovak part of the Danube River, formerly inhabited only by one native gobiid species (Proterorhinus marmoratus). The study of their food habits proved that the amphipod Corophium curvispinum, chironomid larvae and pupae, caddis fly larvae (Hydropsyche sp.) and mayfly nymphs (Ephoron virgo, Potamanthus luteus) were the most important items indicating the food similarity (competition) between the each species. Its extent depended predominantly upon the food resources available. Fish (0+ Zingel zingel and Sander lucioperca) appeared in the diet of N.kessleri only. The competition between N.fluviatilis and N.kessleri was very high at the Danube River sampling site, whilst being quite low in the Hron River. The main items attributed to diet overlapping between the two species were Corophium curvispinum and Hydropsyche sp. Chironomid larvae and pupae were the main point of N.fluviatilis competition with respect to N.melanostomus and to Proterorhinus marmoratus.

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