A model for including fish communities in biotic indices and its role in assessing the water quality and ecological status of lotic systems

Poznavanje distribucije vrsta kao i uspešnost predviđanja njihovog prisustva, od posebnog je značaja za upravljanje akvatičnim biodiverzitetom i procenu intenziteta antropogenog uticaja na vodene ekosisteme. Poslednjih decenija, potreba za restauracijom i očuvanjem akvatičnih ekositema, dovela je do razvoja efikasnih ekoloških pristupa, baziranih na biološkim podacima, za procenu ekološkog statusa u mnogim zemljama sveta. Prema Evropskoj Okvirnoj Direktivi o Vodama (WFD) fauna riba se smatra neizostavnom grupom akvatičnih organizama u proceni ekološkog statusa tekućih voda. Zbog toga, biotički indeksi zasnovani na zajednici riba bivaju u sve češćoj primeni u proceni i monitoringu ekološkog statusa akvatičnih ekosistema. Ciljevi ovog istraživanja bili su: analiza prostorne dinamike zajednice riba, procena značaja sredinskih faktora u strukturiranju zajednice i testiranje ekološke relevantnosti a priori klacifikacije staništa pomoću sredinskih varijabli korišćenjem ihtiofaune kao biotičke komponente. Konačno, kao poseban cilj ističe se definisanje vrsta indikatora kvaliteta vode i staništa, kao i formulacija novog pristupa za procenu kvaliteta i ekološkog statusa tekućih voda, korišćenjem riba kao bioindikatora, koji odražava regionalne specifičnosti Srbije. Uzorci su sakupljeni u periodu od 2003. do 2011. godine, na 124 lokaliteta raspoređenih duž slivova Velike Morave i Drine (Crnomorski sliv), i 7 lokaliteta na rekama koje pripadaju Egejskom slivu. Za grupisanje uzoraka korišćena je metoda Veštačkih neuro mreža, Kohoneove samoorganizujuće mape (eng. self-organizing map (SOM)), koja se, prema dosadašnjim studijama, pokazala veoma pouzdanom za primenu u ekološkim studijama. Za definisanje prostorne organizacije ribljih zajednica posmatrani su lokaliteti sa slivnog područja Velike Morave. Tom prilikom, SOM analiza je, na osnovu biomase ribljih vrsta, ukazala na prisustvo dve grupe uzoraka, X i Y. Grupa Y se sastoji od lokaliteta smeštenih na donjim tokovima reka, dok je grupa X dalje podeljena na podgrupe X1 (srednji tokovi reka) i X2 (gornji tokovi reka). Rezultati su pokazali da klasifikacija ribljih zajednica u velikom stepenu odgovara a priori klasifikaciji na osnovu sredinskih promenljivih. Pojedina odstupanja posledica su intenzivnog delovanja antropogenog faktora. Klasifikaciona snaga (CS) ima veće vrednosti kada se radi o grupama lokaliteta podeljenih na osnovu SOM analize u odnosu na a priori definisane grupe. Sredinski parametri, nadmorska visina i dominantni supstrat, pokazali su se kao faktori od posebnog značaja za strukturiranje zajednice. Takođe, SOM analiza je u ovom radu primenjena je i sa ciljem grupisanja lokaliteta u karakteristične ekološke entitete, tipove reka, u zavisnosti od tipa staništa. Dobijeni tipovi reka su tokom dalje obrade podataka, uz pomoć k- means klaster analize, grupisani u četiri grupe, pri čemu svaka grupa odovara određenom ekološkom stanju. Indikatorske vrste su definisane za svaku grupu na osnovu njihove konstantnosti i dominantnosti. Gradijent na SOM mreži je praćen za jedanaest metričkih osobina. Od ukunog broja posmatranih metričkih osobina, pokazalo se da devet pokazuje jasan gradijent na SOM mapi, dok su Kruskall–Wallis ANOVA i Mann–Whitney test ukazali da se samo tri metričke osobine statistički značajno razlikuju između svih grupa. Rezultati ovog istraživanja prikazuju prostornu organizaciju ribljih zajednica što značajno može doprineti njihovoj implementaciji u programe bioprocene. Na osnovu odabranih metričkih osobina i indikatorskih vrsta, dat je model, zasnovan na zajednici riba, za procenu ekološkog statusa tekućih voda Srbije (fBNBI). Značaj ovog rada leži u činjenici da je fBNBI prvi pokušaj prilagođavanja IBI-a (Indeksa Biotičkog Integriteta) regionalnoim specifičnostima Srbije, koji bi omogućio procenu ekološkog statusa tekućih voda Srbije i detekciju vodotokova koji zahtevaju zaštitu i restauraciju. Konačno, kako bi se postigla pouzdana i sveobuhvatna procena ekološkog stanja, BNBI i fBNBI bi trebalo primenjivati istovremeno.Knowledge of a species’ distribution and the capacity to predict its occurrence are considered essential for managing aquatic biodiversity and assessing the anthropogenic alterations in river environments. In the last decades, the necessity of the restoration and maintenance of healthy aquatic ecosystems has led to the development of practical and effective ecological tools based on biological data in many countries. According to the European Water Framework Directive (WFD), fish fauna is considered as a mandatory group of aquatic biota in the evaluation of the ecological status of running waters. Therefore, fish biotic indices have become common tools for measuring and monitoring the ecological status of aquatic ecosystems. The aim of the study was to analyze spatial variation in the fish assemblages, to investigate the importance in environmental factors in structuring the community and to test the ecological relevance of the a priori landscape classification using fish as biological data. Finally, our specific goal was to define indicator species for each group of water and habitat quality class and to develop the first fish-based model for stream quality assessment in Serbia taking into account the regional specificity of the country. Fish samples were collected between 2003. and 2011. at 124 sampling sites, distributed along the Great Morava and Drina river basins (Black sea drainage basin) and 7 sites belonging to Aegean Sea drainage basin. The fish samples were patterned using an Artificial Neural Network (ANN) technique, the Kohonen self-organizing map (SOM), which is considered to be efficient tool in determining patterns of aquatic ecological assemblages. То explore spatial variaion of fish assemblages, only sites belonging to Great Morava river basin are considered and were patterned using the self-organizing map (SOM) based on fish biomass data. The SOM analysis distinguished two main clusters of samples collected on the Great Morava river basin, X and Y. The Y concerns the downstream areas, while the X was subdivided to the sub-clusters X1 (midstream areas) and X2 (upstream areas). Generally, the classification of the fish assemblages derived by SOM is in accordance with the a priori landscape classification to a greater extent. The significant anthropogenic influence is responsible for the misclassification of some particular sites. The classification strength (CS), derived from the fish community classification obtained by SOM, was higher than for a priori defined groups. Environmental parameters, which the landscape classification is based on, such as altitude and dominant substrate, are found to be very important for community structure. Also, the selforganizing map (SOM) was employed in order to group samples into their characteristic ecological entities (river types) depending on the character of the habitat they came from. Then, the k-means cluster analysis classified samples into four groups, each describing a particular ecological condition. The indicator species were presented for each group based on their constancy and dominance. Gradients over the SOM map were sought for eleven fish community metrics. Out of the total number of tested metrics, nine showed a clear gradient over the SOM map, but the Kruskall–Wallis ANOVA and Mann–Whitney tests pointed out that only three significantly differ among all groups. The results of this study reveal the spatial organization of fish communities which could help their implementation in rapid bioassessment programs. On the basis of the fish community metrics and selected indicator species, we proposed a fish-based index for the assessment of the ecological status of running waters in Serbia (fBNBI). The significance of our work lies on the fact that fBNBI is the first attempt regarding IBI (Index of Biotic Integrity) adjustment to the regional-specificity of Serbian running waters. It would be a clear benchmark to judge the ecological quality of lotic systems in Serbia and to identify waters most in need of protection or restoration. Finally, to assure the reliable and comprehensive assessment of ecological condition we feel that the BNBI and fBNBI should be employed simultaneousl

Community concordance in lotic ecosystems: How to establish unbiased congruence between macroinvertebrate and fish communities

Community concordance within aquatic biota could provide useful information for improving the methods used in bioassessment and biodiversity conservation management. The main goal of the study was to investigate the mechanism of community concordance between macroinvertebrates and fish in a single river basin (South Morava river Basin, Serbia). In order to achieve this, a Self organizing map (SOM) ordinated and classified sampling sites based on the community structures of five different taxa groups (macroinveretbrates (MIB), fish (FSH), Chironomidae (CHI), Macroinvertebrates without Chironomidae (MWC) and the Ephemeroptera Plecoptera Trichioptera group (EPT)). SOM also revealed 6 environmental gradients along the groups tested that significantly changed their community structures. Using the results of the SOM analysis as the input, the Mantel test quantified the highest community concordance between FSH and MIB (r = 0.42) followed by FSH and CHI (r = 0.29). The lowest concordance was recorded between FSH and EPT (r = 0.14). The indicator species analysis (IndVal) revealed 39 species to be responsible for the community patterns obtained. The Geo-SOM visualized the spatial distribution of the IndVal taxa, revealing the generators of community concordance. The strength of community concordance depends on the variability of the data on the aquatic biota. Thus, having an appropriate sampling and statistical design as well as high taxonomic resolution, as some of the factors which increase the variability in the data set, could present community concordance between fish and macroinvertebrates in an unbiased way.Ecological Indicators (2017), 83: 474-48

Predicting Retention Effects of a Riparian Zone in An Agricultural Landscape: Implication for Eutrophication Control of the Tisza River, Serbia

We explored the long-term influence of land use in the riparian zone on the water quality of the Tisza River, as a model of a non-wadeable lowland river located in a temperate, predominantly agricultural landscape. The analysis was based on a comparison of water quality variables between three river sites having contrasting, but constant land use patterns (in 500 m upstream radius) during the study period (2006-2019). While the first river site was characterized primarily by forests, the second and the third were dominated by urban and agricultural areas respectively. The variables which showed a significant difference between the pairs of sampling sites were oxygen saturation, nitrite nitrogen, total nitrogen, and orthophosphates. In contrast to urban and agricultural land, riparian forests showed a positive long-term influence on the river water quality. Natural and seminatural forests and shrubs had a favorable long-term influence on nutrient concentrations and oxygen regime of the Tisza River. However, the retention effects of orthophosphates and nitrite/nitrate content here were relatively low, demonstrating the limited performance of riparian buffers as a main or only management option in the Pannonian landscape, as the agricultural hotspot of Central and Eastern Europe. In conclusion, the riparian buffer assessment design applied in this study may be successfully used in pre-restoration monitoring, prior to the construction of buffer strips

A model for including fish communities in biotic indices and its role in assessing the water quality and ecological status of lotic systems

Poznavanje distribucije vrsta kao i uspešnost predviđanja njihovog prisustva, od posebnog je značaja za upravljanje akvatičnim biodiverzitetom i procenu intenziteta antropogenog uticaja na vodene ekosisteme. Poslednjih decenija, potreba za restauracijom i očuvanjem akvatičnih ekositema, dovela je do razvoja efikasnih ekoloških pristupa, baziranih na biološkim podacima, za procenu ekološkog statusa u mnogim zemljama sveta. Prema Evropskoj Okvirnoj Direktivi o Vodama (WFD) fauna riba se smatra neizostavnom grupom akvatičnih organizama u proceni ekološkog statusa tekućih voda. Zbog toga, biotički indeksi zasnovani na zajednici riba bivaju u sve češćoj primeni u proceni i monitoringu ekološkog statusa akvatičnih ekosistema. Ciljevi ovog istraživanja bili su: analiza prostorne dinamike zajednice riba, procena značaja sredinskih faktora u strukturiranju zajednice i testiranje ekološke relevantnosti a priori klacifikacije staništa pomoću sredinskih varijabli korišćenjem ihtiofaune kao biotičke komponente. Konačno, kao poseban cilj ističe se definisanje vrsta indikatora kvaliteta vode i staništa, kao i formulacija novog pristupa za procenu kvaliteta i ekološkog statusa tekućih voda, korišćenjem riba kao bioindikatora, koji odražava regionalne specifičnosti Srbije. Uzorci su sakupljeni u periodu od 2003. do 2011. godine, na 124 lokaliteta raspoređenih duž slivova Velike Morave i Drine (Crnomorski sliv), i 7 lokaliteta na rekama koje pripadaju Egejskom slivu. Za grupisanje uzoraka korišćena je metoda Veštačkih neuro mreža, Kohoneove samoorganizujuće mape (eng. self-organizing map (SOM)), koja se, prema dosadašnjim studijama, pokazala veoma pouzdanom za primenu u ekološkim studijama. Za definisanje prostorne organizacije ribljih zajednica posmatrani su lokaliteti sa slivnog područja Velike Morave. Tom prilikom, SOM analiza je, na osnovu biomase ribljih vrsta, ukazala na prisustvo dve grupe uzoraka, X i Y. Grupa Y se sastoji od lokaliteta smeštenih na donjim tokovima reka, dok je grupa X dalje podeljena na podgrupe X1 (srednji tokovi reka) i X2 (gornji tokovi reka). Rezultati su pokazali da klasifikacija ribljih zajednica u velikom stepenu odgovara a priori klasifikaciji na osnovu sredinskih promenljivih. Pojedina odstupanja posledica su intenzivnog delovanja antropogenog faktora. Klasifikaciona snaga (CS) ima veće vrednosti kada se radi o grupama lokaliteta podeljenih na osnovu SOM analize u odnosu na a priori definisane grupe. Sredinski parametri, nadmorska visina i dominantni supstrat, pokazali su se kao faktori od posebnog značaja za strukturiranje zajednice. Takođe, SOM analiza je u ovom radu primenjena je i sa ciljem grupisanja lokaliteta u karakteristične ekološke entitete, tipove reka, u zavisnosti od tipa staništa. Dobijeni tipovi reka su tokom dalje obrade podataka, uz pomoć k- means klaster analize, grupisani u četiri grupe, pri čemu svaka grupa odovara određenom ekološkom stanju. Indikatorske vrste su definisane za svaku grupu na osnovu njihove konstantnosti i dominantnosti. Gradijent na SOM mreži je praćen za jedanaest metričkih osobina. Od ukunog broja posmatranih metričkih osobina, pokazalo se da devet pokazuje jasan gradijent na SOM mapi, dok su Kruskall–Wallis ANOVA i Mann–Whitney test ukazali da se samo tri metričke osobine statistički značajno razlikuju između svih grupa. Rezultati ovog istraživanja prikazuju prostornu organizaciju ribljih zajednica što značajno može doprineti njihovoj implementaciji u programe bioprocene. Na osnovu odabranih metričkih osobina i indikatorskih vrsta, dat je model, zasnovan na zajednici riba, za procenu ekološkog statusa tekućih voda Srbije (fBNBI). Značaj ovog rada leži u činjenici da je fBNBI prvi pokušaj prilagođavanja IBI-a (Indeksa Biotičkog Integriteta) regionalnoim specifičnostima Srbije, koji bi omogućio procenu ekološkog statusa tekućih voda Srbije i detekciju vodotokova koji zahtevaju zaštitu i restauraciju. Konačno, kako bi se postigla pouzdana i sveobuhvatna procena ekološkog stanja, BNBI i fBNBI bi trebalo primenjivati istovremeno.Knowledge of a species’ distribution and the capacity to predict its occurrence are considered essential for managing aquatic biodiversity and assessing the anthropogenic alterations in river environments. In the last decades, the necessity of the restoration and maintenance of healthy aquatic ecosystems has led to the development of practical and effective ecological tools based on biological data in many countries. According to the European Water Framework Directive (WFD), fish fauna is considered as a mandatory group of aquatic biota in the evaluation of the ecological status of running waters. Therefore, fish biotic indices have become common tools for measuring and monitoring the ecological status of aquatic ecosystems. The aim of the study was to analyze spatial variation in the fish assemblages, to investigate the importance in environmental factors in structuring the community and to test the ecological relevance of the a priori landscape classification using fish as biological data. Finally, our specific goal was to define indicator species for each group of water and habitat quality class and to develop the first fish-based model for stream quality assessment in Serbia taking into account the regional specificity of the country. Fish samples were collected between 2003. and 2011. at 124 sampling sites, distributed along the Great Morava and Drina river basins (Black sea drainage basin) and 7 sites belonging to Aegean Sea drainage basin. The fish samples were patterned using an Artificial Neural Network (ANN) technique, the Kohonen self-organizing map (SOM), which is considered to be efficient tool in determining patterns of aquatic ecological assemblages. То explore spatial variaion of fish assemblages, only sites belonging to Great Morava river basin are considered and were patterned using the self-organizing map (SOM) based on fish biomass data. The SOM analysis distinguished two main clusters of samples collected on the Great Morava river basin, X and Y. The Y concerns the downstream areas, while the X was subdivided to the sub-clusters X1 (midstream areas) and X2 (upstream areas). Generally, the classification of the fish assemblages derived by SOM is in accordance with the a priori landscape classification to a greater extent. The significant anthropogenic influence is responsible for the misclassification of some particular sites. The classification strength (CS), derived from the fish community classification obtained by SOM, was higher than for a priori defined groups. Environmental parameters, which the landscape classification is based on, such as altitude and dominant substrate, are found to be very important for community structure. Also, the selforganizing map (SOM) was employed in order to group samples into their characteristic ecological entities (river types) depending on the character of the habitat they came from. Then, the k-means cluster analysis classified samples into four groups, each describing a particular ecological condition. The indicator species were presented for each group based on their constancy and dominance. Gradients over the SOM map were sought for eleven fish community metrics. Out of the total number of tested metrics, nine showed a clear gradient over the SOM map, but the Kruskall–Wallis ANOVA and Mann–Whitney tests pointed out that only three significantly differ among all groups. The results of this study reveal the spatial organization of fish communities which could help their implementation in rapid bioassessment programs. On the basis of the fish community metrics and selected indicator species, we proposed a fish-based index for the assessment of the ecological status of running waters in Serbia (fBNBI). The significance of our work lies on the fact that fBNBI is the first attempt regarding IBI (Index of Biotic Integrity) adjustment to the regional-specificity of Serbian running waters. It would be a clear benchmark to judge the ecological quality of lotic systems in Serbia and to identify waters most in need of protection or restoration. Finally, to assure the reliable and comprehensive assessment of ecological condition we feel that the BNBI and fBNBI should be employed simultaneousl

The Influence of Contracaecum larvae (Nematoda, Anisakidae) Parasitism on the Population of Prussian carp (Carassius gibelio) in Lake Sakadaš, Croatia

Contracaecum larvae are geographically widely distributed, utilizing many animal species as hosts; and fish represent an important paratenic host in their life cycle. Their presence in Prussian carp (Carassius gibelio) was studied in Lake Sakadaš (Croatia) in 2017 and 2018. Two gill nets of different sizes submerged during a 12-h period were used to collect the fish. Contracaecum larvae were recorded in the stomach, slightly coiled or elongated on the intestine serosa or encapsulated in a gut wall of 20 individuals. The effect of Contracaecum sp. on the health of their host was determined by estimating the effect of the parasites’ presence, number, and biomass on fish length, weight, and the Fulton’s condition factor (CF). Infected fish showed negative (b < 3; p < 0.05) and uninfected fish positive allometric growth (b > 3; p < 0.05). Fish weight and CF in infected individuals were significantly low in comparison to the uninfected ones (Mann–Whitney U test: U = 1078.00, U = 423.50, respectively; p < 0.004). These results emphasize the importance of evaluating parasitic nematode presence in economically important fish species. Even more, if this endoparasite has a detectable negative impact on a resilient species such as the Prussian carp, it is important to monitor its occurrence in other fish species

The response of chironomid taxonomy- and functional trait-based metrics to fish farm effluent pollution in lotic systems

The lotic habitats affected by trout farm waste are colonized with a particular invertebrate community of which chironomids are the most abundant group. However, there is little information available regarding how chironomid community structures respond to this type of pollution at the highest taxonomic resolution. Eight fish farms, together with their lotic systems as recipients, were used to test the variability of the chironomid community and its surrogates (taxonomic and functional metrics) across spatially arranged sampling sites to form a gradual decrease in the trout farm influence. The self organizing map (SOM) classified six different types of chironomid communities which were characteristic for both the control and affected habitats. The species indicator analyses listed 32 taxa as positive indicators of water pollution. The SOM and Kruskal-Wallis test revealed that the pattern of chironomid community structure obtained was mainly driven by six environmental parameters (Altitude, conductivity, distance from the outlet, hardness, HN4-N, NO3-N). Categorical principal components analysis (CATPCA) derived three models for each type of biotic metric, in which for diversity-, taxonomy- and functional feeding group-based metrics, the first two dimensions explained 55.2%, 58.3% and 55.4%, of the total variance respectively for 315 sampling sites. According to this analysis, the total number of taxa (S), abundance and the Shannon-Wiener index (H') (as a diversity metric), as well as the proportion of Tanypodinae (as taxonomic group) and grazers/scraper (GRA) and gatherer collector (GAT)(as FFG metrics), were related to the outlet distance gradient, thus showing great potential to be used in the multimetric approach in bioassessment

The application of uniform manifold approximation and projection (UMAP) for unconstrained ordination and classification of biological indicators in aquatic ecology

The analysis of community structure in studies of freshwater ecology often requires the application of dimensionality reduction to process multivariate data. A high number of dimensions (number of taxa/environmental parameters x number of samples), nonlinear relationships, outliers, and high variability usually hinder the visualization and interpretation of multivariate datasets. Here, we proposed a new statistical design using Uniform Manifold Approximation and Projection (UMAP), and community partitioning using Louvain algorithms, to ordinate and classify the structure of aquatic biota in two-dimensional space. We present this approach with a demonstration of five previously published datasets for diatoms, macrophytes, chironomids (larval and subfossil), and fish. Principal Component Analysis (PCA) and Ward's clustering were also used to assess the comparability of the UMAP approach compared to traditional approaches for ordination and classification. The ordination of sampling sites in 2-dimensional space showed a much denser, and easier to interpret, grouping using the UMAP approach in comparison to PCA. The classification of community structure using the Louvain algorithm in UMAP ordinal space showed a high classification strength for data with a high number of dimensions than the cluster patterns obtained with the use of a Ward's algorithm in PCA. Environmental gradients, presented via heat maps, were overlapped with the ordination patterns of aquatic communities, confirming that the ordinations obtained by UMAP were ecologically meaningful. This is the first study that applies UMAP and classification using Louvain algorithms on ecological datasets. We show that the performance of local and global structures, as well as the number of clusters determined by the algorithm, make this approach more powerful over the traditional ones.Peer reviewe

Toxic effects of a cyanobacterial strain on Chironomus riparius larvae in a multistress environment

Cyanobacteria and their toxic metabolites present a global threat to water habitats, but their impact on aquatic organisms in a multistress environment has been poorly investigated. Here we present the results of a survey on the effects of the toxic cyanobacterial strain Trichormus variabilis (heterotypic synonym Anabaena variabilis), and its toxic metabolite, cyanotoxin microcystin-LR, on Chironomus riparius larvae in a multistress environment. An environmentally relevant concentration of microcystin-LR (0.1 mg/L) caused an increase in larvae mortality in an acute toxicity test, which became greater in the presence of environmental stressors (NO3−, NH4+, PO43− and Cd2+), pointing to an additive effect of these agents. Chronic exposure of C. riparius larvae to the microcystin-LR producing strain of T. variabilis in a multistress environment led to a reduction in the larval mass and hemoglobin concentration, and it induced DNA damage in larval somatic cells. The results revealed the additive effect of microcystin-LR in combination with all three tested stressors (NO3−, NH4+, PO43−), and the deleterious effect of chronic exposure of C. riparius larvae to the microcystin-LR producing T. variabilis in a multistress environment. However, the present study further emphasizes the importance of investigating interactions between stressors and cyanotoxins, and their effect on aquatic organisms.This is a manuscript of an article published as Stanković, Nikola, Boris Jovanović, Ivana Kostić Kokić, Milica Stojković Piperac, Jelica Simeunović, Dimitar Jakimov, Ivica Dimkić, and Djuradj Milošević. "Toxic effects of a cyanobacterial strain on Chironomus riparius larvae in a multistress environment." Aquatic Toxicology (2022): 106321. doi:10.1016/j.aquatox.2022.106321. Posted with permission.This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 License

Diet seasonality and food overlap of Perca fluviatilis (Actinopterygii: Perciformes: Percidae) and Rutilus rutilus (Actinopterygii: Cypriniformes: Cyprinidae) juveniles: A case study on Bovan Reservoir, Serbia

European perch, Perca fluviatilis Linnaeus, 1758 and roach, Rutilus rutilus (Linnaeus, 1758) are the most common species present in mesotrophic and eutrophic lakes throughout Europe. Their biomass, especially in juvenile stages, contributes the most to the fish production of these ecosystems. In Bovan Reservoir, these two species constitute the bulk of the juvenile fish biomass. This study aimed to investigate the feeding composition of these two species in order to evaluate their niche overlap due to the availability of resources during different seasons. Traditional diet analysis indices and Kohonen artificial neural network (i.e., a self-organizing map, SOM) were used to investigate the diet of 158 individuals of both species and evaluate their food niche overlap. The indicator value (IndVal) was applied to identify indicator food categories based on which the contents of their alimentary tracts were grouped first into neurons and then into clusters on the SOM. Our results showed that juvenile fish used zooplankton and benthic prey in their diet. Roach often fed on nonanimal prey, while perch of age 0+ used fishes in the diet. Additionally, four clusters of neurons were isolated on the SOM output network. The distribution of perch and roach alimentary tracts in neurons indicated no high degree of competition between them. While diet analyses indices show which food category is generally important in specimensʼ diet, the SOM recognizes those specimens and arranges them together into the same or adjacent neurons based on dominant prey. Understanding fish feeding habits is critical for the development of conservation and management plans. Since Bovan is a eutrophic reservoir, our knowledge of fish feeding habits needs to be considered for stocking strategies in the future

The potential of chironomid larvae-based metrics in the bioassessment of non-wadeable rivers

The chironomid community in non-wadeable lotic systems was tested as a source of information in the construction of biological metrics which could be used into the bioassessment protocols of large rivers. In order to achieve this, we simultaneously patterned the chironomid community structure and environmental factors along the catchment of the Danube and Sava River. The Self organizing map (SOM) recognized and visualized three different structural types of chironomid community for different environmental properties, described by means of 7 significant abiotic factors (a multi-stressor gradient). Indicator species analysis revealed that the chironomid taxa most responsible for structural changes significantly varied in their abundance and frequency along the established environmental gradients. Out of 40 biological metrics based on the chironomid community, the multilayer perceptron (MLP), an supervised type of artificial neural network, derived 5 models in which the abundance of Paratrichocladius rufiventis, Orthocladiinae, Cricotopus spp., Cricotopus triannulatus agg. and Cricotopus/Orthocladius ratio achieved a significant relationship (the r Pearson's linear correlation coefficient > 0.7) with the multi stressor environment. The sensitivity analysis “partial derivatives” (PaD) method showed that all 5 biological metrics within the multi-stressor gradient were mostly influenced by dissolved organic carbon (DOC). Despite short and monotonous environmental gradients and the absence of reference conditions, the chironomid community structure and biological metrics predictably changed along the multistress range, showing a great potential for the bioassessment of large rivers