PHYTOPLANKTON COMPOSITION AT THE FISH AND SHELLFISH FARM IN THE KALDONTA BAY (CRES ISLAND)

Uvala Kaldonta nalazi se na jugozapadnoj obali otoka Cresa u Lošinjskom kanalu na području bez većeg utjecaja opće morske struje. U uvali su postavljena 44 plutajuća kaveza veličine 5x10 metara u kojima se uspješno proizvodi oko 70 tona morske ribe: komarča (Sparus aurata), lubin (Dicentrarchus labrax), pic (Diplodus puntazzo) i zubatac (Dentex dentex). Uz neke fizikalnokemijske pokazatelje (temperatura mora, prozirnost, salinitet), posebna je pozornost posvećena kvalitativnom sastavu mrežnog fitoplanktona, a istraživanje je provedeno tijekom godine 2003. (svibanj, rujan, prosinac) i 2004. (veljača) na pet lokaliteta u uvali Kaldonta (Slika 1), na dubinama od 0,5 m, 5 m, 10 m, 20 m i 1 metar iznad dna. Prema fizikalnim i kemijskim pokazateljima, temperatura mora bila je pod utjecajem temperature okoliša, a prozirnost upućuje na oligotrofiju istraživanog akvatorija tijekom istraživanog razdoblja. U kvalitativnom sastavu mrežnog fitoplanktona, utvrđena je 161 vrsta mikrofita, a pripadale su sistematskim odjeljcima Cyanobacteria, Chrysophyta i Dinophyta (Tablica 1). Najbrojnija skupina alga bile su dijatomeje ili Bacillariophyceae (98 vrsta ili 61%) s relativnim učestalostima vrsta od 1 do 7. Taksonomski sastav dijatomeja upućuje na dominantnu zajednicu Chaetoceros –Rhizosolenia (Proboscia), a najviše dijatomejskih vrsta nađeno je u kasnojesenskom razdoblju (početak prosinca). Subdominantan brojnošću vrsta bio je odjel Dinophyta (55 vrsta ili 34,1%), s dominantnim vrstama rodova Ceratium i Protoperidinium. Tijekom istraživanja predstavnici spomenutog odjela nisu pokazivali veliku raznolikost vrsta u vodenom stupcu. Relativna učestalost vrsta bila je uglavnom 1, rjeđe 2 i 3, a najviše je dinofita nađeno u rujnu. Od Cyanobacteria (5 vrsta ili 3,1%) utvrđene su samo nitaste alge s relativnom frekvencijom od 1 do 3. Kvalitativni sastav mrežnog fitoplanktona upućuje na sličan sastav vrsta u vodenom stupcu na svim istraživanim lokalitetima. Prema dobivenim karakteristikama mrežnog fitoplanktona, istraživani lokaliteti čine stabilan ekosustav.The Kaldonta Bay is situated at the south–western coast of the Cres island in the Lošinj channel, rather protected from larger influence of general sea water current. In the Bay there are installed 44 floating cages of 5 by 10 m dimensions. The cages are used for the culture of about 70 tons of sea water fish: gilthead sea bream (Sparus aurata), sea bass (Dicentrarchus labrax), sharp–snouted sparus (Diplodus puntazzo) and dentex (Dentex dentex). Besides some physico–chemical parameters (sea water temperature, transparence and salinity), special attention has been paid to the qualitative composition of net phytoplankton. Investigations were performed in the period of May, September and December 2003 and February 2004 at five locations in the Kaldonta Bay (Figure 1) at the depths of 0.5 m, 5 m, 10 m and 1 m from the bottom. According to the physico–chemical parameters, sea water temperature was influenced by the temperature of the environment, and the transparence suggested to the oligotrophic situation in the investigated aquatorium. Qualitative composition of net phytoplankton comprised 161 microphytic species belonging to the systematic compartments of Cyanobacteria, Chrysophyta and Dinophyta (Table 1). The most numerous algal group were diatoms or Bacillarophyceae (98 species or 61%), with relative frequencies of species from 1 to 7. Taxonomic composition of diatoms showed Chaetoceros–Rhizosolenia (Proboscia) to be the dominant community. Diatom species was the most abundant in late autumn period (beginning of December). The second most important comparatment were Dinophyta (55 species or 34.1%), with the dominant genera Ceratium and Protoperidinium. During the investigation, the representatives of Dinophyta did not show large variety of species in the water column. Relative frequency of the species was 1, rarely 2 and 3. Dinophyts were the most abundant in September. From Cyanobacteria (5 species or 3.1%) only filamentous algae were determined, with relative frequency from 1 to 3. Qualitative composition of net phytoplankton suggests the similarity of species composition in the water column at all the investigated locations. From all characteristics of net phytoplankton that were obtained conclusion can be made that all the investigated locations represent stable ecosystems

PHYTOPLANKTON COMPOSITION AT THE FISH AND SHELLFISH FARM IN THE KALDONTA BAY (CRES ISLAND)

Uvala Kaldonta nalazi se na jugozapadnoj obali otoka Cresa u Lošinjskom kanalu na području bez većeg utjecaja opće morske struje. U uvali su postavljena 44 plutajuća kaveza veličine 5x10 metara u kojima se uspješno proizvodi oko 70 tona morske ribe: komarča (Sparus aurata), lubin (Dicentrarchus labrax), pic (Diplodus puntazzo) i zubatac (Dentex dentex). Uz neke fizikalnokemijske pokazatelje (temperatura mora, prozirnost, salinitet), posebna je pozornost posvećena kvalitativnom sastavu mrežnog fitoplanktona, a istraživanje je provedeno tijekom godine 2003. (svibanj, rujan, prosinac) i 2004. (veljača) na pet lokaliteta u uvali Kaldonta (Slika 1), na dubinama od 0,5 m, 5 m, 10 m, 20 m i 1 metar iznad dna. Prema fizikalnim i kemijskim pokazateljima, temperatura mora bila je pod utjecajem temperature okoliša, a prozirnost upućuje na oligotrofiju istraživanog akvatorija tijekom istraživanog razdoblja. U kvalitativnom sastavu mrežnog fitoplanktona, utvrđena je 161 vrsta mikrofita, a pripadale su sistematskim odjeljcima Cyanobacteria, Chrysophyta i Dinophyta (Tablica 1). Najbrojnija skupina alga bile su dijatomeje ili Bacillariophyceae (98 vrsta ili 61%) s relativnim učestalostima vrsta od 1 do 7. Taksonomski sastav dijatomeja upućuje na dominantnu zajednicu Chaetoceros –Rhizosolenia (Proboscia), a najviše dijatomejskih vrsta nađeno je u kasnojesenskom razdoblju (početak prosinca). Subdominantan brojnošću vrsta bio je odjel Dinophyta (55 vrsta ili 34,1%), s dominantnim vrstama rodova Ceratium i Protoperidinium. Tijekom istraživanja predstavnici spomenutog odjela nisu pokazivali veliku raznolikost vrsta u vodenom stupcu. Relativna učestalost vrsta bila je uglavnom 1, rjeđe 2 i 3, a najviše je dinofita nađeno u rujnu. Od Cyanobacteria (5 vrsta ili 3,1%) utvrđene su samo nitaste alge s relativnom frekvencijom od 1 do 3. Kvalitativni sastav mrežnog fitoplanktona upućuje na sličan sastav vrsta u vodenom stupcu na svim istraživanim lokalitetima. Prema dobivenim karakteristikama mrežnog fitoplanktona, istraživani lokaliteti čine stabilan ekosustav.The Kaldonta Bay is situated at the south–western coast of the Cres island in the Lošinj channel, rather protected from larger influence of general sea water current. In the Bay there are installed 44 floating cages of 5 by 10 m dimensions. The cages are used for the culture of about 70 tons of sea water fish: gilthead sea bream (Sparus aurata), sea bass (Dicentrarchus labrax), sharp–snouted sparus (Diplodus puntazzo) and dentex (Dentex dentex). Besides some physico–chemical parameters (sea water temperature, transparence and salinity), special attention has been paid to the qualitative composition of net phytoplankton. Investigations were performed in the period of May, September and December 2003 and February 2004 at five locations in the Kaldonta Bay (Figure 1) at the depths of 0.5 m, 5 m, 10 m and 1 m from the bottom. According to the physico–chemical parameters, sea water temperature was influenced by the temperature of the environment, and the transparence suggested to the oligotrophic situation in the investigated aquatorium. Qualitative composition of net phytoplankton comprised 161 microphytic species belonging to the systematic compartments of Cyanobacteria, Chrysophyta and Dinophyta (Table 1). The most numerous algal group were diatoms or Bacillarophyceae (98 species or 61%), with relative frequencies of species from 1 to 7. Taxonomic composition of diatoms showed Chaetoceros–Rhizosolenia (Proboscia) to be the dominant community. Diatom species was the most abundant in late autumn period (beginning of December). The second most important comparatment were Dinophyta (55 species or 34.1%), with the dominant genera Ceratium and Protoperidinium. During the investigation, the representatives of Dinophyta did not show large variety of species in the water column. Relative frequency of the species was 1, rarely 2 and 3. Dinophyts were the most abundant in September. From Cyanobacteria (5 species or 3.1%) only filamentous algae were determined, with relative frequency from 1 to 3. Qualitative composition of net phytoplankton suggests the similarity of species composition in the water column at all the investigated locations. From all characteristics of net phytoplankton that were obtained conclusion can be made that all the investigated locations represent stable ecosystems

PRELIMINARY PLANKTON INVESTIGATIONS IN THE GRAVEL PIT AND WINTERPONDS NEAR JAGODNO

Istraživanja planktonskih populacija provedena su na šljunčari i u dvama zimnjacima, smještenima kod mjesta Jagodnog (Novo Čiče) nedaleko od Velike Gorice. Svrha rada bila je istražiti sastav planktona šljunčare i zimnjaka, dvaju ekosustava sa specifičnim životnim uvjetima koji se mijenjaju u vremenu i prostoru. Istraživanje je provedeno tijekom lipnja godine 2007. Uzorci planktona sakupljani su u površinskome sloju na četirima lokalitetima. Na šljunčari su odabrana dva lokaliteta, a u svakom zimnjaku po jedan. Uz sakupljanje planktonskih uzoraka, mjereni su neki fizikalno–kemijski pokazatelji (temperatura vode, pH–vrijednost, količina otopljenog kisika u vodi). Temperatura vode na dvama lokalitetima u šljunčari i u dvama zimnjacima ovisila je o temperaturi okolnoga zraka, a kretala se od 22,5 do 23,6 ºC. pH–vrijednost imala je lužnatu ili alkaličnu reakciju od 8,23 do 9,02, a količina otopljenog kisika u šljunčari bila je oko 10 mg/O2, a u zimnjacima se kretala od 7,6 do 9,7 mg/O2 (Tablica 1). Na istraživanim lokalitetima šljunčare utvrđene su ukupno 32 fitoplanktonske vrste, a u zimnjacima je determinirano 37 mikrofita, dok je zooplankton u sastavu planktonske zajednice na četirima lokalitetima sudjelovao s 5 vrsta. Utvrđene fitoplanktonske vrste u uzorcima s dvaju lokaliteta iz šljunčare pripadale su sistematskim skupinama: Dinophyta, Chrysophyta i Chlorophyta, dok su u zimnjacima, uz spomenute skupine, sudjelovali i predstavnici skupina Cyanophyta/Cyanobacteria i Euglenophyta. Zooplanktonske vrste pripadale su skupinama Rotatoria, Cladocera i Copepoda (Tablica 2). Na istraživanim lokalitetima u šljunčari prevladavale su dijatomeje ili Bacillariophyceae, dok su u zimnjacima glavnu fitomasu činili predstavnici skupina Cyanophyta/Cyanobacteria i Euglenophyta. Kvalitativnim analizama planktona utvrđene su planktonske vrste koje su karakteristične za ciprinidne ribnjake. P–B indeks saprobnosti na istraživanim lokalitetima šljunčare imao je vrijednost 1,7 (kakvoća vode I. vrste), a na lokalitetima 3 i 4, imao je vrijednosti 2,0, odnosno 1,9 (II. vrsta). Na osnovi dobivenih rezultata, istraživani su lokaliteti pogodni za uzgoj ciprinidnih vrsta riba.Investigations of plankton populations have been performed in the gravel pit and two winterponds near the place Jagodno, Novo Čiće, in the vicinity of Velika Gorica. Our goal was to examine plankton composition of the gravel pit and winterponds, two ecosystems characterized by specific life–conditions which change with time and space. Investigations were conducted during June 2007. Plankton samples were collected from water surface layer at four locations (two locations in the gravel pit and one location in each of two winterponds). Along with plankton sample collecting, measurements were made of some physico–chemical parameters (water temperature, pH–values and dissolved oxygen content in water). Water temperature at two sampling locations in the gravel pit and one location at each of the winterponds depended on the surrounding air temperature, and ranged from 22.5ºC to 23.6ºC. pH–reaction was alkaline, ranging from 8. 23 to 9. 02. Dissolved oxygen content in the gravel pit was around 10 mg/O2; in winterponds it ranged from 7.6 to 9.7 mg/O2 (Table 1). At the gravel pit locations total number of 32 phytoplankton species were determined; in winterponds were determined 37 (microphytic species)? while zooplankton was represented in the phytoplankton community composition at the four locations with 5 species. Phytoplankton species determined in the samples from two gravel pit locations belonged to the system groups Dinophyta, Chrysophyta and Chlorophyta while in the samples from winterpond locations, along with the mentioned system groups, were found as well the representatives from the groups Cyanophyta/Cyanobacteria and Euglenophyta. Zooplankton species belonged to the groups Rotatoria, Cladocera and Copepoda (Table 2). In gravel pit locations dominated diatoms or Bacillarophyceae while in winterponds the majority of phytoplankton mass consisted of the representatives of the species Cyanophyta/Cyanobacteria and Euglenophyta. Qualitative analyses of plankton showed the presence of plankton species characteristic for ciprinid fishponds. At gravel pit locations, the saprobity value of P–B (saprobity — saprobicity)? index was 1.7 (characteristic for the first class water quality). At the locations 3 and 4 (winterpond locations) the P–B (saprobity — saprobicity)? index was 2.0 and 1.9, respectively (characteristic for the second class water quality). Based on the obtained results, the investigated locations are suitable for ciprinid fish culture

MICROPHYTOBENTHOS IN THE VRANA LAKE (CRES ISLAND)

Vransko jezero jedno je od najvećih slatkovodnih jezera na relativno malom i zatvorenom krškom otoku. Prema fizikalnim i kemijskim pokazateljima, to jezero je oligotrofno, monomiktičnog karaktera sa zimskom cirkulacijom i ljetnom termalnom stratifikacijom. Istraživanje mikrofitobentosa provedeno je u studenome 1995., te u veljači, svibnju, lipnju, kolovozu i studenome godine 1996. i 1997. Uzorci mikrofitobentosa sabirani su grabilom na pet lokaliteta (Slika 1): V1 (oko 13 m), V2 (oko 22 m), V3 (oko 33 m), V4 (oko 51 m) i V5 (oko 73 m). U kvalitativnom sastavu mikrofitobentosa, utvrđeno je 138 vrsta mikrofita koji su pripadali sistematskim skupinama: Cyanobacteria, Bacillariophyceae i Chlorophyceae (Tablice 1 i 2). Najbrojnija skupina bila je Bacillariophyceae (99 vrsta ili 71,7%) s relativnim učestalostima vrsta od 1 do 6. Najzastupljeniji u strukturi mikrofitobentosa bili su planktonski oblici Campylodiscus noricus i Cyclotella radiosa. Relativno malim brojem vrsta bile su zastupljene skupine Chlorophyceae (26 vrsta ili 18,8%) i Cyanobacteria (13 vrsta ili 9,5 %). Nazočnost pojedinih vrsta Chlorophyceae u strukturi mikrofitobentosa bila je pojedinačna s niskom relativnom učestalošću, uglavnom 1, osim vrste Mougeotia sp. koja je imala relativnu učestalost 3 na lokalitetima V1 i V2. Od Cyanobacteria prevladavale su nitaste alge roda Lyngbya i Phormidium s relativnom frekvencijom od 1 do 5. Od ukupnoga broja utvrđenih vrsta u mikrofitobentosu, 94 vrste ili 68% bile su indikatori saprobnosti. Najviše je bilo oligosaprobnih do betamesosaprobnih indikatora. Na osnovi indikatorskih vrijednosti nađenih vrsta u mikrofitobentosu tijekom istraživanja, P–B indeks saprobnosti kretao se od 1,3 do 1,7 (Tablica 3), što upućuje na dobru kakvoću jezerske vode.Lake Vrana represents one of the largest freshwater lakes on a relatively small and entirely karstified island. According to its physical and chemical factors, this lake is ologotrophic, monomictic, with winter circulation and thermal stratification in summer. Microphytobenthic investigations of the Lake were performed in November 1995, and in February, May, June, August and November of 1996 and 1997, respectively. During the investigations microphytobenthic samples have been collected at five locations (Figure 1): V1 (around 13 m depth), V2 (around 22 m depth), V3 (around 33 m depth), V4 (around 51 m depth) and V5 (around 73 m depth). Qualitative microphytobenthic composition consisted of 138 microphytic species belonging to: Cyanobacteria, Bacillariophyceae and Chlorophyceae (Tables 1, 2). Bacillariophyceae were the most numerous (99 species or 71.7 %), with relative frequency from 1 to 6. Planktonic forms Campylodiscus noricus and Cyclotella radiosa were the most represented species in microphytobenthic structure. The groups Chlorophyceae and Cyanobacteria were represented with relatively small number of species, the former with 26 species or 18.8% and the latter with 13 species or 9.5%. Particular species of Chlorophyceae were represented individually in microphytobenthic structure with low relative frequency, mostly 1, except in the case of Mougeotia sp. which had relative frequency 3 at the locations V1 and V2. The filamentous algae of the genera Lyngbya and Phormidium were dominant among Cyanobacteria, with relative freguency from 1 to 5. From the total number of microphytobenthic species determined, 94 species or 68% belonged to saprobic indicators. Most of them were oligosaprobic to betamesosaprobic indicators. Based on indicator values for the determined microphytobenthic species, P–B saprobity index was ranging between 1.3 and 1.7 (Table 3), which suggests good quality of lake waters

PHYSICAL-CHEMICAL AND BIOLOGICAL CHARACTHERISTICS OF CARP PONDS

Voda kao životni prostor djeluje na sva živa bića svojim fizikalnim i kemijskim osobitostima (abiotičkim pokazateljima) te biološkim karakteristikama (biotičkim pokazateljima). Promjenljivost pojedinih pokazatelja vodenoga staništa ima značajni učinak na organizme koji žive u vodi. Abiotički i biotički pokazatelji vrlo su važni za održavanje specifičnih ekosustava kao što su ribnjaci. Od mnogih ovih pokazatelja u radu su spomenuti samo neki, najosnovniji, može se reći i najvažniji. Od fizikalnih pokazatelja u ribnjacima važnu ulogu imaju temperatura, strujanje vode, svjetlost, prozirnost i boja, te gustoća vode, a od kemijskih čimbenika važni su kisik, odnosno količina otopljenog kisika u vodi, količina ugljičnog dioksida u vodi, koncentracija vodikovih iona, hranjive soli i tvrdoća vode. Biotički pokazatelji uključuju živi svijet, bilo planktonski bilo bentonsni, te više vodeno bilje u ribnjacima, koji upućuju na trofiju tih ekosustava. Svi ti pokazatelji utječu na produktivno st ribnjaka, odnosno na lošu ili dobru proizvodnju riba.As a habitat, water influences all the living creatures with its physical and chemical (non-biotic indicators) as well as biological characteristics (biotic indicators). The unsteadiness of particular indicators of the water environment has a significant effect on organisms living in water. The nonbiotic and biotic indicators are very important for maintenance of the specific ecosystems like fish ponds. Among many indicators this work mentions only a few basic and the most important ones. Regarding the physical indicators in the fish ponds temperature, water streaming, light, transparency, col our and water density have an important role, while as chemical factors oxygen, i. e. oxygen saturation level, carbon dioxide saturation level, concentration of the hydrogen ions, nutritious salts and water hardness are important. The biotic indicators include the living organisms, either planctonic or benthosic, and higher water plants in fish ponds, which indicate "the trophicness of these ecosystems. All these indicators influence the productivity of the fish ponds, i. e. good and bad fish production

MICROPHYTOBENTHOS IN THE VRANA LAKE (CRES ISLAND)

Vransko jezero jedno je od najvećih slatkovodnih jezera na relativno malom i zatvorenom krškom otoku. Prema fizikalnim i kemijskim pokazateljima, to jezero je oligotrofno, monomiktičnog karaktera sa zimskom cirkulacijom i ljetnom termalnom stratifikacijom. Istraživanje mikrofitobentosa provedeno je u studenome 1995., te u veljači, svibnju, lipnju, kolovozu i studenome godine 1996. i 1997. Uzorci mikrofitobentosa sabirani su grabilom na pet lokaliteta (Slika 1): V1 (oko 13 m), V2 (oko 22 m), V3 (oko 33 m), V4 (oko 51 m) i V5 (oko 73 m). U kvalitativnom sastavu mikrofitobentosa, utvrđeno je 138 vrsta mikrofita koji su pripadali sistematskim skupinama: Cyanobacteria, Bacillariophyceae i Chlorophyceae (Tablice 1 i 2). Najbrojnija skupina bila je Bacillariophyceae (99 vrsta ili 71,7%) s relativnim učestalostima vrsta od 1 do 6. Najzastupljeniji u strukturi mikrofitobentosa bili su planktonski oblici Campylodiscus noricus i Cyclotella radiosa. Relativno malim brojem vrsta bile su zastupljene skupine Chlorophyceae (26 vrsta ili 18,8%) i Cyanobacteria (13 vrsta ili 9,5 %). Nazočnost pojedinih vrsta Chlorophyceae u strukturi mikrofitobentosa bila je pojedinačna s niskom relativnom učestalošću, uglavnom 1, osim vrste Mougeotia sp. koja je imala relativnu učestalost 3 na lokalitetima V1 i V2. Od Cyanobacteria prevladavale su nitaste alge roda Lyngbya i Phormidium s relativnom frekvencijom od 1 do 5. Od ukupnoga broja utvrđenih vrsta u mikrofitobentosu, 94 vrste ili 68% bile su indikatori saprobnosti. Najviše je bilo oligosaprobnih do betamesosaprobnih indikatora. Na osnovi indikatorskih vrijednosti nađenih vrsta u mikrofitobentosu tijekom istraživanja, P–B indeks saprobnosti kretao se od 1,3 do 1,7 (Tablica 3), što upućuje na dobru kakvoću jezerske vode.Lake Vrana represents one of the largest freshwater lakes on a relatively small and entirely karstified island. According to its physical and chemical factors, this lake is ologotrophic, monomictic, with winter circulation and thermal stratification in summer. Microphytobenthic investigations of the Lake were performed in November 1995, and in February, May, June, August and November of 1996 and 1997, respectively. During the investigations microphytobenthic samples have been collected at five locations (Figure 1): V1 (around 13 m depth), V2 (around 22 m depth), V3 (around 33 m depth), V4 (around 51 m depth) and V5 (around 73 m depth). Qualitative microphytobenthic composition consisted of 138 microphytic species belonging to: Cyanobacteria, Bacillariophyceae and Chlorophyceae (Tables 1, 2). Bacillariophyceae were the most numerous (99 species or 71.7 %), with relative frequency from 1 to 6. Planktonic forms Campylodiscus noricus and Cyclotella radiosa were the most represented species in microphytobenthic structure. The groups Chlorophyceae and Cyanobacteria were represented with relatively small number of species, the former with 26 species or 18.8% and the latter with 13 species or 9.5%. Particular species of Chlorophyceae were represented individually in microphytobenthic structure with low relative frequency, mostly 1, except in the case of Mougeotia sp. which had relative frequency 3 at the locations V1 and V2. The filamentous algae of the genera Lyngbya and Phormidium were dominant among Cyanobacteria, with relative freguency from 1 to 5. From the total number of microphytobenthic species determined, 94 species or 68% belonged to saprobic indicators. Most of them were oligosaprobic to betamesosaprobic indicators. Based on indicator values for the determined microphytobenthic species, P–B saprobity index was ranging between 1.3 and 1.7 (Table 3), which suggests good quality of lake waters

PHYTOPLANKTON COMPOSITION IN FISH FARMS ALONG THE EASTERN ADRIATIC COAST

Investigations of net phytoplankton composition were performed at three fish farms situated at the northern, middle and southern part of the eastern Adriatic Sea coast, respectively. In the northern part investigations were conducted in the Limski kanal, in the middle part at the Ugljan island and in the southern part in the place Drače on the Pelješac peninsula (Figure 1). At all three localities fish culture included mostly two species: gilthead sea bream (Sparus aurata) and sea bass (Dicentrarchus labrax). Beside some physico–chemical parameters (sea water temperature, salinity) special attention was placed on the examination of qualitative net phytoplankton composition, which was conducted in the period of May and November 2004 and May and October 2005. Samples were collected at the depths of 0. 5 and 4 meters. According to the physico–chemical parameters, sea water temperature was influenced by the temperature of the environment. Qualitative net phytoplankton composition consisted of 153 microphytic species belonging to the systematic compartments of Cyanobacteria, Chrysophyta and Dinophyta (Table 1). The most numerous algal group were diatoms or Bacillarophyceae (84 species or 55%) with relative frequencies of species from 1 to 7. Taxonomic composition of diatoms showed the community Chaetoceros–Rhizosolenia (Proboscia) as the dominant one. The second numerically most dominant compartment were Dinophyta (62 species or 401%) with dominant the species of the genera Ceratium and Protoperidinium. Relative frequencies of species was ranging from 1 to 7 (mass presence of specimens in the water column). From Cyanobacteria (4 species or 3%), only filamentous algae were determined, with individual presence in net phytoplankton composition. Qualitative net phytoplankton composition suggests the similarity of species composition in the water column at all investigated fish farms. From the obtained characteristics of net phytoplankton composition conclusion can be made that all investigated localities constituted stable ecosystems