4th CROATIAN CONGRESS OF MICROBIOLOGY WITH INTERNATIONAL PARTICIPATION

Od 24. do 27. rujna 2008. u hotelu Donat u Zadru održan je Četvrti hrvatski mikrobiološki kongres s međunarodnim sudjelovanjem. Kongresu je prethodila radionica »Adenoviruses — basic biology to gene therapy«, a organizator obaju skupova bilo je Hrvatsko mikrobiološko društvo

GENOTYPING OF ISOLATED VIRUSES FROM RAINBOW TROUT (ONCORHYNCHUS MYKISS) IN CROATIA

Infectious hematopoietic necrosis virus (IHNV) and infectious pancreatic necrosis virus (IPNV) are important pathogens in rainbow trout aquaculture. Detection of these viruses in Croatia initiated investigation of their genetic relatedness to the worldwide IHNV and IPNV isolates. For this purpose, determination of nucleotide sequences of G and NV genes for IHNV and VP2/NS region for IPNV was performed. Phylogenetic analyses revealed that Croatian IHNV isolate was clustering within European clade most closely related to the North American M genogroup. Croatian IPNV isolate appeared in the cluster of genogroup III, together with French, English, Danish and Norwegian isolates. These results are important for further epidemiological studies of IHNV and IPNV outbreaks in Croatia

ENVIRONMENTAL IMPACTS OF TUNA AQUACULTURE IN THE ADRIATIC SEA

Razvoj akvakulture, pa tako i tova tuna, u posljednjim je desetljećima, povećao zanimanje javnosti za moguće utjecaje na okoliš. Istraživanja utjecaja uzgoja gospodarski važnih ribljih vrsta su brojna, ali ne i u pogledu procjena mikrobioloških utjecaja, a napose ne u kontekstu tova tuna. Cilj ovog istraživanja bio je procijeniti utjecaj tova tuna (Thunnus thynnus) na okoliš na temelju praćenja mikrobioloških pokazatelja kakvoće morske vode na tovilištu tuna u srednjem Jadranu, te ostvarene rezultate usporediti s rezultatima istraživanja na tovilištu tuna u Mediteranu. Kakvoća morske vode analizirana je na dva lokaliteta, pri čemu je jedan lokalitet bio na tovilištu tuna, a drugi na udaljenosti oko 500m od tovilišta i poslužio je kao tzv. kontrolna točka. Uzorkovanje je provedeno u dvije sezone (proljeće/jesen), u 2007. i 2008. godini. Tijekom ovog istraživanja, analizirani su osnovni fizikalno-kemijski (temperatura, salinitet, prozirnost) i mikrobiološki parametri (ukupan broj bakterija, Vibrio, ukupni koliformi, Escherichia coli, fekalni koliformi, enterokoki) kakvoća morske vode. Za mikrobiološku analizu uzorci morske vode serijski su razrijeđeni s PBS otopinom (Merck). Za određivanje ukupnog broja heterotrofnih bakterija, uporabljene su metodom širenja razmaza dvije podloge, Marine agar (BBL) i Trypticase soy agar (BBL) s dodatkom 1% NaCl-a (Kemika), te supstrat metoda s uporabom SimPlate testa (IDEXX), sve u duplikatu. Za određivanje broja ukupnih koliforma i E. coli, odnosno enterokoka uporabljeni su supstrat testovi Colilert (IDEXX), odnosno Enterolert (IDEXX) u duplikatu. Utvrđene vrijednosti broja heterotrofnih bakterija, koje ukazuju na utjecaje tovilišta u vidu eutrofikacije mora, ukupno su manje od vrijednosti utvrđenih u istraživanjima poduzetim na tovilištima tuna u Mediteranu. Broj E. coli i enterokoka nije značajno različit između tovilišta i kontrolne točke, ali su te vrijednosti veće u odnosu na dosadašnja istraživanja na sličnim tovilištima u Mediteranu. Povećani broj enterokoka u uzorcima mora, i oko tovilišta, najvjerojatnija je indirektna posljedica nepravilne tehnologije hranidbe, koja privlači kolonije galebova. Ovi rezultati ukazuju da promjene kakvoće morske vode, a u svezi s tovom tuna, ovise o širem ekološkom kontekstu. Stoga, smještaj i procjenu utjecaja tova na okoliš valja razmatrati u sklopu šireg ekološkog konteksta područja.Aquaculture including tuna fattening, increased public interests in the possible impact on the environment in recent decades. Influences of cultivation of economically important fish species are numerous, but not in regard to assessment of microbial influences, particularly in the context of tuna. The aim of this study was to assess the effects of tuna fattening (Thunnus thynnus) in the sense of the environmental monitoring of microbial indicators of seawater quality at tuna farm in the central Adriatic, and to compare the achieved results with the results of research on a tuna farm in the Mediterranean. The quality of sea water was analyzed at two sites; one site was at the tuna farm, and the other at a distance of about 500m from the farm, the control point. Sampling was conducted in two seasons (spring / autumn), in 2007 and 2008. During this study, the basic physico-chemical (temperature, salinity, transparency) and microbiological parameters of seawater quality (total number of bacteria, Vibrio, total coliforms, Escherichia coli, faecal coliforms, enterococci) were analyzed. For microbiological analysis of seawater; samples were serially diluted with PBS solution (Merck). To determine the total number of heterotrophic bacteria, spread plate method was used on Marine agar (BBL) and Trypticase soy agar (BBL) supplemented with 1% NaCl-a (Kemika), as well as substrate method using SimPlate test (IDEXX), all in duplicate. To determinate total coliforms and E. coli, and enterococci substrate tests Colilert (IDEXX) and Enterolert (IDEXX) were used in duplicate. Number of heterotrophic bacteria, which indicate the effects of the farm on the eutrophication, was less than the number determined in similar study in the Mediterranean. Number of E. coli and enterococci were not significantly different between farm and control point, but these values are higher than those from research in the Mediterranean. Increased numbers of enterococci, on the farm and control point, were indirect consequence of improper nutrition technology, which attracted a colony of seagulls. These results suggest that changes in seawater quality in relation to tuna fattening, depend on the broader ecological context. Therefore, location and environmental impact of tuna fattening on the environment must be considered within the broader context of ecological areas

Effects of low and high irradiation levels on growth and PSII efficiency in Lemna minor L.

Plant growth and reproduction depend on light energy that drives photosynthesis. In the present study we compared growth characteristics, photosynthetic pigments content and photosystem II (PSII) performance in Lemna minor L. grown in two different irradiation regimes: low light (LL) – 50 μmolPHOTONS m-2 s-1 and high light (HL) – 500 μmolPHOTONS m-2 s-1. The main goal was to investigate the photosynthetic regulatory mechanisms that ensure adjustment to different light conditions and integrate these observations with the data on plant multiplication and biomass production. For this purpose, we measured chlorophyll (Chls) and carotenoid (Cars) contents and analyzed the energy fluxes through the PSII by saturation pulse method as well as by Chl a transient induction and JIP test. In a comparison of the effect of LL and HL on plant multiplication and fresh biomass, it was shown that the effect on growth was primarily attributed to the biomass reduction in LL while the effect on number of plants was much smaller. Total Chl and Cars contents were decreased in plants exposed to HL which indicated long-term acclimation response to the increased irradiance. Furthermore, the HL plants revealed better capability for the utilization of absorbed light in photosynthesis accompanied by photoprotective adjustment of certain number of PSII reaction centers from active to dissipative mode of functioning. In conclusion, our study showed that duckweed plants had great adjustment potential to different irradiation conditions, which might be of great importance not only under variable light availability but also when simultaneously challenged by some other environmental disturbance (e.g. different pollutants)

HEALTH STATUS OF CHUB (Squalius cephalus) IN RELATION TO WATER QUALITY OF SAVA RIVER

Voda kao životni okoliš organizama koji u njoj žive svojom kvalitetom utječe na njihovo zdravstveno stanje. U dostupnoj je literaturi malo podataka o pokazateljima zdravstvenoga stanja klena, osobito iz rijeke Save. Zbog toga je svrha ovog istraživanja bila procijeniti zdravstveno stanje klena kao pokazatelja kvalitete vode, te odrediti odnos histoloških i parazitoloških pokazatelja prema broju bakterija u vodi. Istraživanje je provedeno na ukupno 289 klenova s pet postaja od slovensko–hrvatske granice do utoka rijeke Une u Savu. Uzorci organa klena uzeti su za parazitološku i histološku pretragu. Istodobno je uzorkovana voda i određen broj heterotrofnih i koliformnih bakterija. Razlike u količini bakterija u vodi bile su izražene među pojedinim postajama. Najviša je vrijednost utvrđena na postaji Oborovo, a najniža na postaji Otok Samoborski. Intenzitet histoloških promjena bio je u korelaciji s mikrobiološkom kakvoćom vode. U svim uzorkovanim organima utvrđen je barem jedan histološki pokazatelj u visokoj korelaciji s mikrobiološkom kakvoćom vode. Od parazitarnih invazija samo su ihtioftirijaza i trihodinijaza pokazale visoku negativnu korelaciju s mikrobiološkom kvalitetom vode. U sklopu parazitološke pretrage primijenjivane su i molekularne metode u svrhu identifikacije crijevnih parazita iz grupe Acanthocephala.Water quality has infuence on the health status of the organisms living in it. In the available literature, there is only a few reports on the health status of chub, particularly in the Sava river. The aim of this study was to estimate health status of chub as indicator of water quality. Furthermore we aimed at relating fish histology and parasitology to the number of bacteria in the water. We sampled 289 chubs for parasitological and histological examination. Fish were sampled on five sites from slovenian–croatian border through to the inflow of river Una in Sava. At the same time, water was sampled for the counting of coliforms and heterotrophic bacteria. The difference in the number of bacteria in the water was pronounced at different locations, with Oborovo and Otok Samoborski having the highest and the lowest values respectively. The intensity of histological parameters was in correlation with the number of bacteria in water. At least one histological parameter highly correlating with the water quality was found in every organ. Regarding parasite invasions, only ichthyophthiriasis and trichodiniasis showed high negative correlation with microbiological quality of the water. As part of parasitological examination, molecular methods were used for the identification of Acanthocephala

Effects of water contamination with heavy metals on pigmented macrophages in spleen of Vardar chub (Squalius vardarensis Karaman) from three rivers in the North-Eastern region of North Macedonia

Background and purpose: Pigmented macrophage aggregates (PMAs) are a part of the immune system of fish and are considered as valuable biomarkers of the impact of water pollution on fish health.Materials and methods: Immunomodulatory effect of water contaminated with high levels of metals on spleen and splenic PMAs of Vardar chub (Squalius vardarensis) (n=129) was examined in two seasons, spring, and autumn 2012. For this purpose, three rivers were chosen: the Zletovska River, heavily contaminated with metals, the Kriva River, moderately contaminated with metals combined with high level of organic matter, and the Bregalnica River, without heavy metal contamination. Spleen masses and splenosomatic indices (SSI) were used for determining the general impact of water contamination on the immune system of Vardar chub. Moreover, volumes and numbers of PMAs within spleen tissue were determined stereologically.Results: The isolated effect of high exposure to metals caused the reduction of spleen mass and/or SSI in the fish from the Zletovska River. The combined effect of exposure to metals and high levels of nutrients in the fish from the Kriva River referred to stimulation of PMAs response, namely increased volumes of splenic PMAs. The existence of seasonally dependent differences was noted since the observed variability in PMAs between rivers occurred only in the autumn.Conclusions: Splenic PMAs in the Vardar chub can be used as an additional biomarker of metal pollution, but with caution, since enhancement of the volumes and numbers of MACs depends on the exposure level of heavy metals, on the presence of the other contaminants, as well as on the physiological condition of the fish

IMPACT OF SALMON FARMING ON WATER QUALITY

Rast akvakulturne proizvodnje potiče i povećano zanimanje i brigu za njezin utjecaj na okoliš. Tijekom salmonidne proizvodnje na ribogojilištu u vodu se unose određene količine organske tvari. Količina visokoproteinske hrane i metabolički riblji proizvodi utječu na kakvoću vode koja se koristi u uzgoju riba. Bakterije imaju ključnu ulogu u razgradnji organske tvari. Prekomjerno obogaćivanje nutrientima dovodi do osiromašenja kisikom kroz mikrobiološku oksidaciju organske tvari i takvi uvjeti nepovoljno utječu na ukupnu kakvoću vodenog ekosustava. Cilj ovih istraživanja bio je procijeniti utjecaj salmonidnog uzgajališta na kakvoću vode na osnovi praćenja dinamike bakterijske populacije i fitobentosa u odnosu na fizikalno-kemijske parametre vode (temperatura, kisik, pH itd.). Istraživanja su provedena na pastrvskom ribogojilištu s godišnjom proizvodnjom oko 100 t ribe, kod protoka vode od oko 300 L/s. Uzorci vode za mikrobiološku obradu i uzorci fitobentosa sakupljeni su na 8 lokaliteta uz istovremeno mjerenje fizikalno-kemijskih parametara elektrosondom. Lokaliteti uzorkovanja odabrani su tako da se obuhvate sve uzgojne faze salmonidnog ribnjaka: ulaz u ribnjak, 4 lokaliteta na ribnjaku po pojedinim fazama uzgoja, na izlazu iz ribnjaka, te uzvodno i nizvodno od ribnjaka. Za određivanje ukupnog broja bakterija (cfu) uzorci vode su serijski razrijeđeni sa sterilnom Ringerovom otopinom pH 6,0 (Pliva) i inokulirani metodom razlijevanja po podlozi na mediju za izolaciju sukladno EN ISO 6222:1999. Nakon inkubacije do 5 dana na 22°C, prebrojane su izrasle bakterijske kolonije i rezultati su izraženi za 1 ml vode (cfu/ml). Dobiveni uzorci bentosa stavljeni su u boce i konzervirani s 4 %-tnim formalinom. Mikroskopska obrada uzoraka obavljena je u laboratoriju, pomoću mikroskopa «Opton» povećanja 12,5 x10; 12,5 x 25 i 12,5 x 40. Relativna zastupljenost vrsta fitobentosa određena je po Knöpp-u, od 1 do 7, (1954), a saprobne vrijednosti indikatorskih vrsta po Wegl-u (1983). Indeks saprobnosti na osnovi indikatorskih biljnih vrsta određen je prema Pantle-Buck-u (1955), te na osnovi dobivenih vrijednosti pokazatelja kakvo_e vode, istraživani lokaliteti svrstani su u određenu vrstu, prema Uredbi o klasifikaciji voda (1998). Fizikalno-kemijske karakteristike vode na istraživanim lokalitetima ne pokazuju u pravilu značajnije razlike. Gustoća populacije aerobnih bakterija pokazuje progresivne promjene na lokacijama unutar uzgajališta, a sukladno očitovanju obogaćenja nutrijentima. Tijekom istraživanja u fitobentosu najbrojnija skupina bile su dijatomeje ili Bacillariophyceae, tipični oblici fitobentoske zajednice. Od ukupnog broja utvrđenih vrsta, više od 50% pripadalo je indikatorima saprobnosti. Indikatorske vrste pripadale su oligosaprobnom i betamesosaprobnom stupnju. Vrijednosti izračunatog indeksa saprobnosti bile su 1,7 na lokalitetima prije i nakon izlaska iz ribogojilišta, te 1,8 na izlazu iz bazena II i III, gdje se nalazi konzumna riba. Vrijednosti P-B indeksa saprobnosti upućuju na kakvoću vode istraživanih lokaliteta na I odnosno II vrstu. Ova mikrobiološka i fitocenološka istraživanja upućuju na zaključak da sam proces uzgoja riba nema većeg utjecaja na kakvoću vode. Utvrđeno je da je voda koja izlazi iz ribnjaka bolje kakvoće od vode recipijenta.Aquaculture production is undergoing a rapid expansion including an increasing interest and concern for their potential impact on the environment. Salmon fish farming releases a substantial amount of organic matter in to the water. High protein fish food and fish excretion affecting the quality of water used in fish farming. Bacteria play the major role in decomposition of the organic matter. Excessive enrichment of nutrients leads to oxygen depletion in the oxidation of the organic matter. Such conditions have negative effects on aquatic environment. The aim of this study was to estimate the impact of salmon farming on the water quality, on the basis of bacterial population and phytobenthos monitoring in relation to physico-chemical water characteristics (temperature, dissolved oxygen, pH etc.). The investigation was carried out on a rainbow trout fish farm with an annual trout production of 100 tons, and water flow of 300 l/s. Water samples for microbiological and phytobenthos analyses were collected at eight locations. Physico-chemical parameters were measured by an electrosonde at the same time. Sampling locations were determined to include all stages of salmon production: entry to the fish farm, four locations on the fish farm at different stages of salmon production, outflow from the fish farm, and locations upstream and down stream from the fish farm. Water samples for the heterotrophic bacteria enumeration (cfu) were serially diluted with Ringer solution pH 6.0 (Pliva) and inoculated by spread plate method on the solid medium according to EN ISO 6222:1999. After incubation at 22 °C for five days colonies were counted and results expressed for 1 ml of water (cfu/ml). Samples for benthos analysis were collected in the bottles and conserved with 4 % formaldehyde. Samples were examined under ‘’Opton’’ light microscope with magnifications 12.5x10; 12.5 x 25 and 12.5 x 40 in the laboratory. Relative phytobenthos assemblage determination from 1 to 7 was performed according to Knöpp (1954), and saprobity measures of indicators species according to Wegl (1983). Index of saprobity was determined according to Pantle-Buck (1955). Examined locations were classified according to ‘’Uredba o klasifikaciji voda’’ (1998) on the basis of the obtained water quality values. Physico-chemical water characteristics were without significant differences on examined locations. Density of the heterotrophic bacteria showed progressive changes on the locations within the fish farm which was consistent with nutrient enrichment. The most frequent species in the phytobenthos were diatoms and Bacillariophyceae, which are typical forms of phytobenthic community. More than 50 % of all determined species belonged to saprobity indicators. Indicator species were characteristic for oligosaprobic and betamesosaprobic water. Saprobity indexes were 1.7 at locations upstream and downstream of the fish farm. At the escit from 2nd and 3rd pool, with consumer fish, saprobity indexes were 1.8. These the values of P-B saprobity index indicate first and second degree water quality of the examined locations. The results of these microbiological and phytocenological examinations lead to the conclusion that fish production has insignificant local impact on the water quality

IMPACT OF SALMON FARMING ON WATER QUALITY

Rast akvakulturne proizvodnje potiče i povećano zanimanje i brigu za njezin utjecaj na okoliš. Tijekom salmonidne proizvodnje na ribogojilištu u vodu se unose određene količine organske tvari. Količina visokoproteinske hrane i metabolički riblji proizvodi utječu na kakvoću vode koja se koristi u uzgoju riba. Bakterije imaju ključnu ulogu u razgradnji organske tvari. Prekomjerno obogaćivanje nutrientima dovodi do osiromašenja kisikom kroz mikrobiološku oksidaciju organske tvari i takvi uvjeti nepovoljno utječu na ukupnu kakvoću vodenog ekosustava. Cilj ovih istraživanja bio je procijeniti utjecaj salmonidnog uzgajališta na kakvoću vode na osnovi praćenja dinamike bakterijske populacije i fitobentosa u odnosu na fizikalno-kemijske parametre vode (temperatura, kisik, pH itd.). Istraživanja su provedena na pastrvskom ribogojilištu s godišnjom proizvodnjom oko 100 t ribe, kod protoka vode od oko 300 L/s. Uzorci vode za mikrobiološku obradu i uzorci fitobentosa sakupljeni su na 8 lokaliteta uz istovremeno mjerenje fizikalno-kemijskih parametara elektrosondom. Lokaliteti uzorkovanja odabrani su tako da se obuhvate sve uzgojne faze salmonidnog ribnjaka: ulaz u ribnjak, 4 lokaliteta na ribnjaku po pojedinim fazama uzgoja, na izlazu iz ribnjaka, te uzvodno i nizvodno od ribnjaka. Za određivanje ukupnog broja bakterija (cfu) uzorci vode su serijski razrijeđeni sa sterilnom Ringerovom otopinom pH 6,0 (Pliva) i inokulirani metodom razlijevanja po podlozi na mediju za izolaciju sukladno EN ISO 6222:1999. Nakon inkubacije do 5 dana na 22°C, prebrojane su izrasle bakterijske kolonije i rezultati su izraženi za 1 ml vode (cfu/ml). Dobiveni uzorci bentosa stavljeni su u boce i konzervirani s 4 %-tnim formalinom. Mikroskopska obrada uzoraka obavljena je u laboratoriju, pomoću mikroskopa «Opton» povećanja 12,5 x10; 12,5 x 25 i 12,5 x 40. Relativna zastupljenost vrsta fitobentosa određena je po Knöpp-u, od 1 do 7, (1954), a saprobne vrijednosti indikatorskih vrsta po Wegl-u (1983). Indeks saprobnosti na osnovi indikatorskih biljnih vrsta određen je prema Pantle-Buck-u (1955), te na osnovi dobivenih vrijednosti pokazatelja kakvo_e vode, istraživani lokaliteti svrstani su u određenu vrstu, prema Uredbi o klasifikaciji voda (1998). Fizikalno-kemijske karakteristike vode na istraživanim lokalitetima ne pokazuju u pravilu značajnije razlike. Gustoća populacije aerobnih bakterija pokazuje progresivne promjene na lokacijama unutar uzgajališta, a sukladno očitovanju obogaćenja nutrijentima. Tijekom istraživanja u fitobentosu najbrojnija skupina bile su dijatomeje ili Bacillariophyceae, tipični oblici fitobentoske zajednice. Od ukupnog broja utvrđenih vrsta, više od 50% pripadalo je indikatorima saprobnosti. Indikatorske vrste pripadale su oligosaprobnom i betamesosaprobnom stupnju. Vrijednosti izračunatog indeksa saprobnosti bile su 1,7 na lokalitetima prije i nakon izlaska iz ribogojilišta, te 1,8 na izlazu iz bazena II i III, gdje se nalazi konzumna riba. Vrijednosti P-B indeksa saprobnosti upućuju na kakvoću vode istraživanih lokaliteta na I odnosno II vrstu. Ova mikrobiološka i fitocenološka istraživanja upućuju na zaključak da sam proces uzgoja riba nema većeg utjecaja na kakvoću vode. Utvrđeno je da je voda koja izlazi iz ribnjaka bolje kakvoće od vode recipijenta.Aquaculture production is undergoing a rapid expansion including an increasing interest and concern for their potential impact on the environment. Salmon fish farming releases a substantial amount of organic matter in to the water. High protein fish food and fish excretion affecting the quality of water used in fish farming. Bacteria play the major role in decomposition of the organic matter. Excessive enrichment of nutrients leads to oxygen depletion in the oxidation of the organic matter. Such conditions have negative effects on aquatic environment. The aim of this study was to estimate the impact of salmon farming on the water quality, on the basis of bacterial population and phytobenthos monitoring in relation to physico-chemical water characteristics (temperature, dissolved oxygen, pH etc.). The investigation was carried out on a rainbow trout fish farm with an annual trout production of 100 tons, and water flow of 300 l/s. Water samples for microbiological and phytobenthos analyses were collected at eight locations. Physico-chemical parameters were measured by an electrosonde at the same time. Sampling locations were determined to include all stages of salmon production: entry to the fish farm, four locations on the fish farm at different stages of salmon production, outflow from the fish farm, and locations upstream and down stream from the fish farm. Water samples for the heterotrophic bacteria enumeration (cfu) were serially diluted with Ringer solution pH 6.0 (Pliva) and inoculated by spread plate method on the solid medium according to EN ISO 6222:1999. After incubation at 22 °C for five days colonies were counted and results expressed for 1 ml of water (cfu/ml). Samples for benthos analysis were collected in the bottles and conserved with 4 % formaldehyde. Samples were examined under ‘’Opton’’ light microscope with magnifications 12.5x10; 12.5 x 25 and 12.5 x 40 in the laboratory. Relative phytobenthos assemblage determination from 1 to 7 was performed according to Knöpp (1954), and saprobity measures of indicators species according to Wegl (1983). Index of saprobity was determined according to Pantle-Buck (1955). Examined locations were classified according to ‘’Uredba o klasifikaciji voda’’ (1998) on the basis of the obtained water quality values. Physico-chemical water characteristics were without significant differences on examined locations. Density of the heterotrophic bacteria showed progressive changes on the locations within the fish farm which was consistent with nutrient enrichment. The most frequent species in the phytobenthos were diatoms and Bacillariophyceae, which are typical forms of phytobenthic community. More than 50 % of all determined species belonged to saprobity indicators. Indicator species were characteristic for oligosaprobic and betamesosaprobic water. Saprobity indexes were 1.7 at locations upstream and downstream of the fish farm. At the escit from 2nd and 3rd pool, with consumer fish, saprobity indexes were 1.8. These the values of P-B saprobity index indicate first and second degree water quality of the examined locations. The results of these microbiological and phytocenological examinations lead to the conclusion that fish production has insignificant local impact on the water quality