Abstract:Results of the investigation of the aquatic macroinvertebrate fauna along a 504 km stretch of the Danube River in Serbia are presented. A total of 74 macroinvertebrate taxa were observed during a 2001 survey. Oligochaeta and Mollusca were the principal components of the community with regard to species richness and abundance. Based on data on the qualitative composition of the macroinvertebrate fauna, a correspondence analysis divided the investigated stretch in three sectors -upper (Pannonian), Iron Gate sector and entrance sector to the Iron Gate stretch. The distribution patterns of certain species supported the division of sectors defined by correspondence analysis.

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The present work cites results of investigating aquatic macroinvertebrates of the Danube River on the sector upstream from the Iron Gate (KM 1083-1071). The investigated part is interesting from the hydrobiological standpoint above all due to differences of faunal composition in relation to higher sections that could be expected in view of differences in overall characteristics of the river. A rich macroinvertebrate community (84 taxa) was observed. The diversity of taxa is primarily a result of habitat diversity within the given stretch. Oligochaeta and Mollusca were the principal components

Detailed and relevant limnological investigations of Serbian waters were initiated in 1958 and have continued to the present. During the period 1971-2008 we monitored biological elements as a part of working studies/projects, including the distribution of the freshwater jellyfish Craspedacusta sowerbyi Lankester, 1880. We observed over 500 sampling sites in running and standing waters. Specimens of this hydro-medusa were found in five of them. Throughout the period of investigation, only the medusae stages were observed. Our purpose in this paper was to provide data of the records and distribution of this limnomedusa during the period 1958-2008 in inland waters of Serbia. These observations should contribute to knowledge on the limnofauna not only of the Balkan Peninsula but Europe as a whole

Recently, dispersion of invasive species became an important theme, since the man-aided outspread of the organisms was recognized as one of the major threats to the biodiversity. Aquatic biotopes are, due to its unique features, among the most disposed ecosystems to this kind of disturbance. Non-indigenous species of different origin were found among plants, vertebrates and invertebrates. Aquatic worm Branchiura sowerbyi (Beddard 1892) is obvious example of human induced dispersal of invertebrates. The aim of the study was to contribute to the cognition of the current distribution of this invasive species and to point up, once again, the risk of devastation of aquatic ecosystems caused by distribution of alien species. B. sowerbyi was for the first time observed in Serbia in 1972 in fish pond in Vojvodina.Since that time the worm spread its areal and now it could be found in a lot of ponds, channels, reservoirs and lowland rivers in Serbia. According to our results B. sowerbyi has been well adapted in artificial and modified water bodies in Serbia.