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U istraživanju provedenom na endemima tulara Plitvičkih jezera, pokušale su se utvrditi njihove ekološke značajke i brojnost te kolika je zaštita potrebna da bi se očuvale prisutne populacije na području Nacionalnog parka.

U studiji su obrađeni rezultati istraženih zajednica riba, makrozoobentosa, zooplanktona, fitoplanktona te fizikalno-kemijskih svojstava vode u akumulaciji Butoniga u 2006. godini. Na osnovu dobivenih rezultata preporučene su mjere za smanjenje trofije u akumulaciji.

This paper presents the results of a two-year study of the macrozoobenthos community in Drava River reservoirs, with special emphasis on the oligochaetes. Sampling was conducted seasonally at two stations on each of the reservoirs (Varaždin, Čakovec and Dubrava). Station 1 was positioned in shallower waters at the beginning of the reservoir while. Station 2 was positioned at the deepest part of the reservoir, near the dam. Oligochaetes constituted the bulk of the total macrozoobenthos in the investigated reservoirs. Larval insects (Diptera) were found with higher densities in the shallow parts of the Čakovec and Dubrava reservoirs. During the study period, 27 taxa of the oligochaetes were reported, belonging to the following families: Tubificidae, Naididae, Lumbriculidae, Lumbricidae and Enchytraeidae. The largest number of taxa was recorded within the families Naididae (13 taxa) and Tubificidae (10 taxa). With the exception of the Varaždin reservoir, the greatest diversity was recorded at Station 1, with lower diversity near the dams. Based on the abundance and diversity of oligochaetes, their share in the macrobenthos community and the share of the taxa Limnodrilus hoffmeisteri, it can be concluded that the Varaždin reservoir has a higher trophic level compared to the other two studies reservoirs. The Dubrava reservoir proved to the lowest trophic intensity.

Uz pomoć makrozoobentosa procjenjivalo se stvarno ekološko stanje Plitvičkih jezera na nekoliko različitih jezera u baražnom sustavu.

Istraživanje na tularima je bilo provedeno duž cijelog toka Cetine na mjesečnoj bazi u trajanju od godine dana. Obrađeno je 11 lokacija gdje su sakupljane i ličinke i odrasle jedinke te su mjereni svi fizikalno-kemijski parametri vode koji su korišteni u daljnim analizama.

The Croatian goby Knipowitschia croatica (Mrakovcic et al., 1994) (Gobiidae) is a critically endangered freshwater goby endemic to the lower Neretva River basin in Croatia. The objective of the study was to examine diet and feeding ecology, seasonally and by sex. Specimens were collected monthly over the course of one year (2006), and samples of macrobenthic organisms were collected in June and November. The results show that the Croatian goby feeds on 9 groups of aquatic macrobenthic invertebrates (Nematoda, Oligochaeta, Amphipoda, Isopoda, Ostracoda, Ephemeroptera, Trichoptera, Coleoptera, Diptera). No plant material was found in any of the digestive tracts. Diptera are present in the adult and larval stages and representated by the families Chironomidae and Ceratopogonidae. The dominant diet elements are amphipods, isopods and chironomid larvae, with a greater diversity (7 groups) recorded in summer than in autumn (3 groups). Differences in feeding habits by sex were established. Females consumed higher numbers of prey throughout the year, which relates to the territorial behaviour of the nesting male, who rarely leaves his nest and feeds only on prey that is readily available within the direct vicinity of the nest. Females feed mainly on chironomid larvae in spring and winter, while in summer and autumn they consumed more gammarids than any other prey. In the diet of males, amphipods were most abundant, representated by gammarids in all seasons except autumn, when the isopod Asellus aquaticus was the dominant prey.

U studiji su izneseni rezultati istraživanja zajednica riba, višeg bilja, makrozoobentosa, fitobentosa, zooplanktona te fitoplanktona. Istraživani su i fizikalno-kemijski parametri vode i mulja u jezerima Savica. Na temelju dobivenih rezultata preporučene su mjere za smanjenje onečišćenja u jezerima.

Tijekom 1995. i 1996. godine izvršena su istraživanja makrozooplanktona Visovačkog jezera. Ukupno je utvrđeno 7 vrsta. Makrozooplankton Visovačkog jezera obilježavaju makrofiltratori - Eudiaptomus hadzici (Copepoda-Calanoi-da), mikrofiltratori — Daphnia logispina i Daphnia cucullata (Cladocera), detritivori — Diaphanosoma brachyurum (Cladocera), omnivori — Mesocjclops leukarti i Cjclops abjssorum (Copepoda-Cyclopoida) i predatori — Leptodora kindtii (Cladocera). U planktonu Visovačkog jezera žive četiri vrste rakova rašljoticalaca (Cladocera). Budući da imaju slične zahtjeve za hranom, njihov je suživot djelomično omogućen prostornom i vremenskom odvojenošću niše. Posebno je zanimljiv odnos dvije vrste Daphnia: D. cucullata i D. longispina. Obje imaju iste potrebe za hranom, ali kada dolaze zajedno pojavljuju se u različitim slojevima vode: D. cucullata u epilimniju i metalimniju, a D. longispina u donjim dijelovima metalimnija i hipolimniju. Vrsta D. cucullata dominantna je tijekom ljeta, a brojnost vrste D. longispina veća je u hladnijem dijelu godine, tj. kada prethodne vrste nema u populaciji. Od abiotičkih čimbenika najveći utjecaj na formiranje makrozooplanktonske zajednice Visovačkog jezera imaju ukupni fosfor i temperatura. Mikrofiltratorski Cladocera pojavljuju se u velikom broju, što ukazuje na dobru &laquo ; top-down&raquo ; regulaciju, karakterističnu za oligotrofna jezera. Ipak, u Visovačkom jezeru ova je ravnoteža pomalo narušena, što se može vidjeti po većoj zastupljenosti detritivornih vrsta.

Zajednica makrozoobentosa istraživana je na četiri postaje uzduž transekta, u donjem bazenu Visovačkog jezera. Postaje su smještene, tako da su obuhvaćene sve dubinske zone jezera (litoralna, sublitoralna. iprofundalna zona). Li-toralna zona je po svom kvalitativnom sastavu najbogatija, dok je dubinska zona najsiromašnija. Brojnošću se ističu dvije skupine faune dna: Oligochaeta i Chironomidae. Brojčani udio hironomida progresivno opada s dubinom, za razliku odoligoheta čiji udio raste s dubinom. Biomasenipak udio obiju skupina raste spovećanjem dubine. Povećanjem dubine mijenjaju se osnovni fizikalno-kemijski uvjeti na staništu, te izvori dostupne hrane, što se odražava i na kvalitativnu i kvantitativnu strukturu faune dna. U litoralnoj zoni lanci ishrane polaze od primarnih producenata, dok je zajednica makrozoobentosa na većim dubinama ovisna o fitoplanktonu i količini organskih čestica u sedimentu. Fauna sakupljača-sabirača je najznačajnija funkcionalna skupina makrokonzumenata. Predstavnici usitnjivača i strugača važni su samo za zajednicu litoralne zone. Dominantna i najčešća vrsta je predstavnik Oligochaeta Pota-mothrix hammoniensis, koji najgušće populacije ima u području sublitorala i profundala.

The composition of caddis larvae assemblages in altered and man-made habitats of the hydro-electric power plant system in the Drava River was studied over two years. All sampled habitats (power plant reservoirs, drainage ditches, tailrace canals and old river flow) were greatly influenced by hydro-technical management. Altogether 31 Trichoptera taxa belonging to 12 families were collected. The highest taxa richness was recorded at site in the old river flow at the first power plant. Silo nigricornis had the highest population density and dominated the communities in drainage ditches due to specific environmental conditions. The trophic relationships of the collected taxa were identified and trophic structure of larval assemblages was analysed. The assemblage structure differed among investigated habitats with passive filter-feeders – predators – grazers, piercers, grazers – detritivores or predators – passive filter-feeders as dominant feeding groups. Through multidimensional scaling (MDS) analysis, differences in the composition of the assemblages between sampling sites and clustering of samples from particular habitat types were identified. The highest clustering of samples was observed for the sites in drainage ditches and the lowest in old river flow.

Fizikalno-kemijske, biološke i ihtiološke značajke voda hidroelektrana na Dravi.

Istraživanja i optimizacija ihtiocenoze u svrhu smanjenja trofije akumulacije Butoniga tijekom 2005. godine

Istraživanja bioloških značajki akumulacija koje pripadaju hidroenergetskom sustavu HE Vinodol.

Fizikalno-kemijske, biološke i ihtiološke značajke voda hidroelektrana na Dravi.

Istraživanja i optimizacija ihtiocenoze u svrhu smanjenja trofije akumulacije Butoniga tijekom 2004. godine

Physicochemical conditions and macroinvertebrate community structure were investigated during 2002/03 in Vrana Lake near Biograd, Croatia. Vrana Lake is the largest natural lake in Croatia. The area of the lake is 30.2 km2, and maximum depth is round 4 m. The lake stretches parallel with the seacoast and it is separated from the Adriatic Sea with an 800-2500 m wide limestone ridge. Salinity of the lake varied from 0.7-1.2 ‰ . Chironomidae and Oligochaeta dominated in the macrozoobenthos, but macroinvertebrate diversity and density were relatively low. During the investigated period, 12 chironomid species were recorded, and the most abundant and common species was Procladius (Holotanypus) sp. The only representative of Oligochaeta was Potamothrix heuscheri (Bretscher). This is the first record of P. heuscheri in lakes along the eastern Adriatic coast.

Elaborat se bavi procjenom kakvoće vode rijeke Une na temelju analize makrozoobentosa uzetog u nekoliko navrata duž toga rijeke Une i analiziranog u laboratoriju.

The macrozoobenthos and macrozooplankton communities of four shallow urban lakes in the centre of Zagreb were investigated from March to December 2003. The lakes are influenced by human activity because they are a part of a big recreational park Maksimir. All lakes share the same drainage area, but three of them are directly connected through the feeding stream Bliznec. Macrozooplankton was collected in each lake, at the deepest point with pulling the plankton net (80 µ ; ; m) in vertical haul from the bottom to the surface. Abundance and biomass were calculated from these quantitative samples. Quantitative samples of macrozoobenthos were collected at two stations in each lake using an Ekman grab (sampling area 0.01 m2). Physico-chemical parameters (dissolved oxygen, oxygen saturation, biological oxygen demand, temperature, pH, total dissolved solids, conductivity, nitrate, nitrite, ammonium, orthophosphate, chlorophyll a and transparency) were also measured. Bliznec stream flows through populated village and city area collecting untreated wastewater from the households. That makes Bliznec the main source of organic and inorganic pollution, which influence benthos and plankton community especially in two shallower lakes (max. depth app. 2 m). Species Bosmina longirostris and some small detritivorous cladocerans dominate macrozooplankton. They are most abundant during summer. Macrozoobenthos is at the same time characterized by large numbers of Tubificidae (70-90% of macroinvertebrate community) especially species Limnodrilus hoffmeisteri, Potamothrix bavaricus, and P. hammoniensis. The other two lakes are deeper (max. depth app. 5-7 m). Copepod Eudiaptomus gracilis and cladoceran Daphnia longispina dominate the plankton community. Portion of Tubificidae family in benthos community is reduced (35-50%). Diversity of Naididae family increased from one to six species, and dipteran families Chironomidae and Chaoboridae make a large part of macroinvertebrate community (28-40%). Chemical parameters especially nitrate and phosphate had high values in two shallower lakes confirming their higher trophic state. These lakes are surrounding the city ZOO, and large flocks of waterfowls are living there and feeding on food thrown from visitors. The other two, deeper lakes, are slightly isolated deeper in the park and surrounded by forest, as an additional source of organic matter.

Istraopživanja u svrhu optimizacije ihtiocenoze tijekom 2004. godine.

In the lotic aquatic biotopes on a tufa barrage in the Plitvice cascade lake system macroinvertebrate samples associated with a calcareous substrate covered with bryophytes and accumulated organic detritus were collected seasonally in four habitats with different current velocities. The aim was to investigate the interaction between the community features of macroinvertebrates and bryophyte cover associated with the selective retention and accumulation of particulate organic matter affected by different water flow conditions. In the tufa barrage habitats, depending on current velocity, bryophyte biomass varied seasonally from 55 g AFDW m-2 to 256 g AFDW m-2. Bryophyte biomass decreased in the tufa habitats exposed to higher current velocity. In the temporal succession from spring to autumn bryophyte biomass decreased, whereas in winter the biomass increased in all studied rheotopes. Regression analysis suggested that the bryophyte biomass significantly decreased linearly with an increase in current velocity. The bryophyte mats, which retained coarse (CPOM), fine (FPOM) and ultra fine (UPOM) benthic particulate organic matter as a food source for the detritial benthic macroconsumers, were significantly related to current velocity. CPOM and FPOM content of the bryophyte mats showed a tendency to increase in habitats with a lower current velocity. Conversely, UPOM content increased in bryophyte habitats with a higher current velocity. Regression analysis suggested that CPOM and FPOM increased whereas UPOM decreased significantly in habitats with a greater bryophyte biomass. In bryophyte habitats the community composition of macroinvertebrates was characterized by small forms of oligochaetes, dipterans and coleopterans constituting from 64.1% to 98.7% of the total number of macroinvertebrate individuals. Regression analysis suggested that macroinvertebrate density increased in faster water flow conditions associated with a decrease in bryophyte biomass, CPOM and FPOM, and an increase of UPOM. Macroinvertebrate community composition and species diversity showed significant differences among the four seasons and four water flow conditions associated with selective retention and accumulation of POM. In bryophyte habitats macroinvertebrate functional feeding composition was characterized by collector fauna increasing their density with faster water flow conditions. In spring and summer collector gatherers were dominant whereas collector-filterers dominated in autumn and scrapers showed a maximum in winter. Regression analysis, using the power model (y = axb), suggested that densities of collectors and predators showed a positive relationship with the quantity of their food sources.

Procjena mogućnosti odvodnja viška vode iz Vrgorskog polja

Shallow Mediterranean lake Jezero has been affected by eutrofication in last four decade. In 1970 the lake has been a subject of phosphorus reduction program with bio manipulation techniques to decrease lake primary production. In the 1974 and 1976 herbivorous and planktivorous fish (silver carp, grass carp) were introduced in the lake. We measured the abundance and biomass of filter-feeding micro crustacean zooplankton, their grazing impact on phytoplankton biomass, and compared it with the results of prebiomanipulation state. Although the species composition remained the same, we observed a shift in the portion of certain taxa in total abundance of crustacean plankton. Large daphnias and calanoid copepods became dominant, while cyclopoid copepods and Bosmina became scarce. Phosphorus reduction lowered phytoplankton biomass, but submerged vegetation was also limited by the lack of phosphorus. Our results indicate that the importance of zooplankton grazing may have minor importance for the maintenance of the clear water state in the lake.

In the paper the results of the longitudinal research of trophic features of the Butoniga reservoir, situated in the middle of the Istria peninsula, will be presented. The research started in 1987, i.e. when the reservoir was formed, and lasted till 200i. The reservoir served as a supplier of drink water and as a ban against floods. The reservoir has the following characteristics: a surtace is 2.3 km3, a volume is of 19*106 m3, a mean depth is 4.5 m, a maximum depth is 11 m and catchments area is 73 km2. It is supplied with water from 3 streams and by inflows what makes possible to change the whole amount of the water twice a year. It has to be pointed out that the water level oscillates more than 4 m. During the mentioned period of time physical-chemical characteristics (temperature, Secchi depth, dissolved oxygen, nutrient concentrations, chlorophyll a), the structure and abundances of zooplankton, phytoplankton, zoobenthos, macrophytes and fish populations were monitored. On the basis of the analyses it has been established that in the period 1987-1990 the reservoir was mild eutrophic, but after that the trophic level was kept on the mezotrophic level. It was mostly due to breakdown of organic materials after filling up of the reservoir. However, since 1998 monitored parameters has been showing the trend of increasing of the atrophic degree, as a consequence of the inflow of nutrients and sediment from a catchments area and uncontrolled introduction of fish of Cyprinidae family (a carp Cyprinus carpio and a prussian carp Carassius auratus gibelio). On the basis of the results of the researches the programme of measures to preserve and improve of water quality of the reservoir as a very important source of drink water has been proposed and accepted. Two types of measures were proposed: mechanical and biological. Among mechanical measures the following ones should be mentioned: resolving the inflow of nutrients and sediment from a catchments area by means of supplying streams, the outflow of lower levels of water at the end of summer and mechanical removal of submerge vegetation. Among biological measures the following was proposed: introducing of planktivorous fish, especially phytoplankton grazing fish (a silver carp Hipophthalmichthys molitrix and predatory fish species (a pikeperch Shiostedion lucioperca) and elimination previously mentioned undesirable fish species.

The diversity, species composition and structure of the fish community of Drava River were studied after impoundment in 1983. Over a period of eighteen years 23, 507 fish specimens were collected which includes 55 different fish species belonging to 16 families. The family Cobitidae is represented by two species: spined loach - Cobitis elongatoides and weather loach &#8211 ; ; ; Misgurnus fossilis, while the family Balitoridae is represented with stone loach - Barbatula barbatula. On eleven of seventeen investigated localities we recorded presence of Cobitidae family, while stone loach were found on six localities. In the studied fish community C. elongatoides is represented with 315 specimens (1.34 % of the total number of individuals), while B. barbatula is represented with 236 specimens (1.00 %). M. fossilis is a pretty rare species with just a seven individuals (0.03 %) caught in 18 years of study. While spined loach and stone loach were first caught in 1985, weather loach was first caught in 1996.

Fizikalno-kemijske, biološke i ihtiološke značajke voda hidroelektrana na Dravi.

The copepod communities of karstic lakes along the eastern Adriatic coast were studied. Lakes were divided in aeveral groups according to their morphology (deep, shallow, barrage and rescrvoirs), production (oligotrophic, mesotophic and eutrophic), and salinity of water: freshwater and brackish. Copidodioptorrtu.s steueri, Euc.vclops serrulotu.s and Macroc_vclop.s albidu.s belong to the group that inhabited most of the lakes under the study, regardless of lake type. The shallow karstic lakes are usually inhabited by Tl~ermoc.vclops dybowskii, T. oithonoides, Cvclops vicimt.s and Eudinptnmus padarws etru.scus in freshwater biotopes, and Cnlanipedicr ayuaedulci.s and Copidodiap tontu.s .steueri in brackish biotopes. The last two species can also be found in deep karstic lakes with brackish water (Bacina lakes in the Neretva River delta). Species like Cvclops abyssorum can be found in most deep freshwater lakes. Some Calanoida were recorded in only one lake, like Eudiaptomus transsvlvanicu.s in the deep Lake Vrana on the island of Cres, or Eudiaptomu.s had~ici in the barrage Lake Visovac. Production of the lakes, expressed as copepod biomass, depends on lake trophy, and in some lakes also on hydrology and salinity. Most of the meso eutrophic lakes in the study area had Calanoida dominating, while Cyclopoida dominated in some oligotrophic and eutrophic lakes as well.

The depth distribution of oligochaetes was studied in Visovac lake (Croatia) along a transect from 1 to a maximum of 24 metres. In the material collected, 21 oligochaete species belonging to 4 families were identified, all of them more or less common in European lakes. The greatest diversity of oligochaetes was found at a depth of 4-6 m (18 taxa). On silty-sands covered by reed decay at a depth of 1 m oligochaetes comprised only 2% of the total benthic biomass. Oligochaeta densities increased with depth and at a depth of 22-24 m they represented 59% of the total biomass. Depth and bottom type were the impor- tant variables in defining species distribution. Only three oligochaete species were found at all of the investigated depths: Potaraothrix hammoniensis, Psarrsrrdoryct,ides 6ar6ntus and Lirnnodrilus hoffraeisteri. Aulodridus plvriseta was distributed only in the area of submerged macrophytes. The remaining species occurred less frequently, and mainly with restricted distribution.

Istraživanja i vrednovanja bioloških značajki rijeke Cetine i njenog porječja

The phytoplankton community of the Čakovec reservoir (hydroelectric power plant on the Drava River) was investigated during 1998. The purpose was to establish the composition, floral similarity, and seasonal distribution of phytoplankton, as well as the saprobity degree of water on investigated profiles. During the investigations the total number of 80 algal taxa was recorded with Diatoms as the dominant group. The total number of cells ranged between 3.6 and 25.8 x 10'/1. The phytoplankton minimum was observed at all profiles during winter, while the maximal number of algae occurred in au- tumn. The most frequent species were Asterionella formosa HASS., Fragilaria crotonen- sis KITT., and Melosira varians AG. The index of similarity ranged between 72.8% and 85.2%. The index of saprobity, based on indicator species found in the phytoplankton community, varied from 1.9 to 2.2.

The length, weight, sex structure and reproduction of the spined loach were observed on spined loach from the delta of the Neretva River. Maximal TL for females was 100.4 mm and for males 63.5 mm. Lamina circularis was visible in specimens not smaller than 45.6 mm. The male : female sex structure was 1:4.4, and in some locations males were not found at all. Males died at the end of the 2+ year season, and females mostly at the end of the 3+ year season. A partial spawning with 4 categories of eggs was established (max 1.3 mm), the maximal number being about 2,500. Spawning occurs two or three times from April to the beginning of August, depending on the size and age of the females.

The description of the Cobitis taenia dalmatina - Dalmatian spined loach (Karaman, 1929) from the river Cetina is very brief and therefore the species can hardly be identified. Some of the authors (Vasiljeva 1988, Vasiljeva et al., 1989) consider that Cobitis taenia is distributed only in the Volga watershed, and in some rivers of the Baltic Sea watershed. The T-test between the females and males showed differences caused by the sexual dimorphism in lengths of the pectoral, ventral and anal fin, head length, head height (above eyes) and minimal height of body. The Dalmatian spined loach has a shorter caudal peduncul, longer pectoral and ventral fins in males, bigger distance between pectoral and ventral fins and smaller interorbital space in the relation of the values obtained by other authors. The number of lateral spots (4th Gambetta zone) is 11-18 and dorsal spots 10-17. The fin formula is D II 8, A (I) II 6(7), P I 8(9), V I 7, C 16. The number of vertebrae is 39-40 and pharyngeal teeth 11 (9-12). The maximal number of eggs was 3,300 in April and maximal egg size is 1.39 mm (in June). Partial spawning was established with four categories of eggs. It was found that the Dalmatian spined loach has two types of lamina circularis and suborbital spine. The shape of scales shows similarity with the Linnean type of the C. taenia (described by Nalbant 1993). The barbels of the Dalmatian spined loach are extremely long. Three types of the colour pattern (Gambetta zones) exist. The caudal fin base spot is brown, line-shaped and placed obliquely. In some specimens this spot is hardly visible or not present at all. Based on these results the Dalinatian spined loach, until now considered as subspecies of Cobitis taenia, should be raised on the species level.

In this paper the distribution of amphipods along two river system (Mura and Drava, northwestern Croatia) is described. Four amphipod species Gammarus fossarum Koch, 1835, G. roeseli Gervais, 1835, Niphargus valachicus Dobreanu & Manolache, 1933 and Synurella ambulans (F. Müller, 1846) were found in this region. In contrast to its oxbow lakes and surrounding fen region the amphipod biodiversity is low in the Mura and Drava River. G. fossarum is dominant and present only in the Mura River due to different environmental conditions in the various habitats and localities. G. roeseli is present in all types of researching habitats with the dominance in ditches. N. valachicus inhabits only eutrophic pools while S. ambulans is present in different kind of habitats viz. drainage ditch, tailrace canal and old river flow without its dominance in those habitats.

Croatian Adriatic river system consists of six rivers with their tributaries: Mirna, Rasa, Zrmanja, Krka, Cetina and Neretva. The presence of genus Cobitis has been recorded in only three of them: Zrmanja, Cetina and Neretva. There are some specimens of genus Cobitis from the river Zrmanja. This area was never studied systematically and therefore there are not enough records to analyse Zrmanja's fish fauna. In the river Cetina genus Cobitis is a rare genus. It lives in a community of five species and represents just a 2.9 percent in total number of fish individuals and 0.14 percent in total biomass (20 years old data). In river Neretva genus Cobitis is a common genus with just a 3.6 percent in total number of fish specimens and 0.38 percent in total biomass. If we compare percentage number of fish individuals for genus Cobitis in Neretva and Cetina, at first sight we would not see a great difference, but the fish community in river Neretva consists of 33 different fish species and genus Cobitis is a very important genus there. In this paper we compare present records of the fish community in the River Cetina with the old one. We also compare fish communities of Neretva and Cetina and analyse status of genus Cobitis in each of them.

From April 1995 to October 1996 the benthic ommunity of the karstic Lake Visovac was studied with special reference to chironomids. By origin, Lake Visovac is a travertine barrage lake and relates to solution lakes. Samples were taken along a transect from 1 to a maximum of 24 meters. Over the entire investigated period, 29 Chironomidae species were recorded. Five subfamilies of Chironomidae were represented: Chironominae (20 species), Tanypodinae (4 species), Orthocladiinae (3 species), Diamesinae (1 species) and Prodiamesinae (1 species). The chironomid community of shallower waters is generally much richer than that of bare mud (the profundal zone). Tanytarsini were the most numerous in the littoral zone, while in sublitoral and profundal zones Chironomini were most abundant. Depth and bottom type were the important variables in defining species distribution. Chironomus gr. plumosus preferred mostly deep waters, while Paratanytarsus lauterborni and species of the genus Tanytarsus favoured shallower waters with a bottom rich in decaying plant fragments. Procladius choreus was found in relatively high abundance at all sampling depths due to its ability to feed on a wide range of food items.

22 fish species were caught in a right lateral channel of the Dubrava Dam on the Drava River as a result of an eleven-year research of fish. Water temperature in this lateral channel is low (13 - 15°C), the flow is quite fast and the amount of oxygen is 4.32-4.42 mgO2/l (41.2 - 44.5 % saturated). In the first year after the Dubrava Dam was built on location 4D fish fauna was similar to that of common European slow-flowing rivers. In the next year fish fauna of slow-flowing rivers turned into fish fauna similar to upper reaches of the river. Common fish species on this location are: the burbot (20.11 %), schneider (17.72%), bullhead (15.61%), trout (10.85%) and chub (7.67%). Shannon-Wiener index of species diversity is 3.44 of the possible maximum 4.46.