INTRODUCTION<\/h2>\n
Many river systems are heavily altered or damaged by human activity [1], such as inappropriate hydromorphological modifications and manipulations at\u00a0hydro-electric power stations [2, 3], introduction of invasive species, excessive input of nutrients, and pollution by hazardoussubstances [3]. These multi-stressors significantly affect entire aquatic ecosystems [1]. Water and its quality play an important role in terms of its usability as an irreplaceable raw material for countless sectors of human activity [4]. The same applies for the environment, to\u00a0which a large number of organisms are bound in part or through their entire life cycle. The use of aquatic organisms (biota) as an indicator of ecological status has a justified significance [5]. Their physiological tolerance and ecological preferences are closely related to the environmental conditions in which they live, and they are able to quickly reflect environmental changes [6,\u00a07]. Bioindicators are widely used to provide useful information about environmental changes or pollution and reflect long-term effects\/stressors that do not act on organisms separately, but simultaneously [8]. Assessment methods are mostly based on the taxonomic composition of the community, which provides information on\u00a0biological interactions, the internal formation of the community, as well as the functioning of the given ecosystem [9]. The\u00a0assemblage of juvenile fish (i.e.\u00a00+, where 0 means no experienced winter and + means an experienced vegetation season) therefore represents a suitable tool for monitoring the ecological status of watercourses, especially because most Bohemian and Moravian watercourses are stocked, i.e.\u00a0subadult and adult fish are released [6]. Juvenile fish (0+) immediately reflect reproductive success or failure in the\u00a0last spawning period and show a significantly faster response to changing environmental conditions than adult fish [6, 10]. In addition to the reproductive success of adult fish, the assemblage of juvenile fish (0+) is influenced by the survival of their early stages, which are very closely linked to the occurrence of suitable micro- to mesohabitats [11], such as shallow areas with sufficient food and shelter, so-called \u201cfish nurseries\u201d [10, 11]. The\u00a0assemblage of juvenile fish (0+) is also shaped by seasonal and inter-seasonal changes in habitats as well as hydrological [12] and temperature regimes, which have a\u00a0significant effect on the overall diversity and abundance of individual species [13, 14]. Environmental changes can be monitored through diversity on a\u00a0local scale, based on species in a given assemblage (\u03b1 diversity) or on a wider scale, between individual assemblages (\u03b2 diversity, [15, 16]). The aim of\u00a0this study was to assess the assemblage of juvenile fish (0+) and the ecological status of watercourses according to the Czech multi-metric index (CZI) within individual basins between 2019 and 2021 at 22 sites that represent closing profiles and important trunk streams in the Czech Republic.<\/span><\/p>\n The biological assessment of the monitored watercourses was carried out using the natural fish assemblage, i.e., juvenile fish (0+). The methodology was compiled in such a way that it was possible to use it to carry out the catch, basic processing and assessment of fish samples (0+) [17, 18]. The chosen methodology represents the current status of the watercourses [19] where only fish that are a maximum of few months old are sampled. The ichthyological survey took place at 22 sites (Fig. 1<\/span>), which were selected on the basis of previous findings from water quality monitoring carried out by the Czech Hydrometeorological Institute [19]. The monitored sites were located in the closing profiles and on the\u00a0trunk streams of the Czech Republic (Fig. 1<\/em>)<\/span>. Sampling sites for catching juvenile fish (0+) were located below municipalities and adjacent agglomerations due to possible influence by technical modifications, weir manipulations, discharge of waste water, and surface sources of pollution, especially in\u00a0important agricultural areas. Thanks to the given sampling design, it was possible to objectively determine the influence of human activity on the assemblage of juvenile fish (0+) between individual basins, as well as across the Czech\u00a0Republic.<\/span><\/p>\n Fish catches (0+) were carried out from the second half of August to the second half of September. Late summer is a suitable period to sample juvenile fish (0+) due to relatively low and stable flows. The abundance of juvenile fish\u00a0(0+) is\u00a0already relatively stable compared to the high mortality that occurs during the first weeks to months after hatching [10]. During this period, juvenile fish\u00a0(0+) still stay in the shallow sections along the banks and do not yet move to the deeper parts of the watercourses (to the wintering grounds), which usually happens during the autumn months [10]. In this period, juvenile fish (0+) are already sufficiently mature, their identification features are similar to adults, and their identification can be carried out directly in the field [17, 20].<\/span><\/p>\n Catching the fish was carried out along the banks of a watercourse (Fig.\u00a02)<\/span> with a battery-powered electric unit (type SEN and LENA from the Bedn\u00e1\u0159 company) with an output frequency of 50\u201395 Hz [10, 21]. The fish were caught using a direct pulsed current, which is not dangerous for the fish\u2019s health in the\u00a0given frequency range [17, 20]. The length of the fished section depended on the\u00a0amount of mesohabitats (shallow stream sections, dead wood, aquatic and flooded terrestrial vegetation, standing water) and ranged from 50\u00a0m to 200\u00a0m (median 100 m). The monitored section was divided into several sub-sections in order to capture a significant part of the environmental variability and the total assemblage of juvenile fish (0+). Following the catch, the fish were identified directly at a given site (Fig. 3<\/em>)<\/span>.<\/span><\/p>\n The ecological status assessment of the monitored watercourses was carried out using the Czech multi-metric index (CZI), which combines several metrics, whose results are combined into a multi-metric output and include several attributes of the assemblage. Metrics that describe and assess environmental conditions include altitude, watercourse order according to Strahler, sea-drainage area, watercourse type (A \u2013 mountain streams to G \u2013 lowland rivers), and typical taxa for a given type of watercourse, as well as non-native species, which significantly reduce the resulting index value [16]. The multi-metric index was calculated according to the following equation:<\/p>\n where<\/p>\n wi\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 is the weight of the metric when calculating CPI<\/p>\n TD\u00a0 \u00a0 \u00a0 \u00a0 number of typical taxa<\/p>\n AR\u00a0 \u00a0 \u00a0 \u00a0 abundance of rheophiles (current-loving species)<\/p>\n ND1\u00a0\u00a0\u00a0\u00a0\u00a0 presence of undesirable species<\/p>\n ND2\u00a0 \u00a0 \u2013 relative representation of undesirable species \u2013 takes on values from 0 to 1 (category CZI, 0\u20130.2 destroyed; > 0.2\u20130.4 damaged; > 0.4\u20130.6 medium; > 0.6\u20130.8 good and > 0.8\u20131 excellent). The upper and lower limits of the metric values are used to calculate the Ecological Quality Ratio (EQR), i.e., the ratio between the detected and expected (reference) values [16].<\/p>\n Differences in the juvenile fish assemblage were assessed in the R software program ver. 4.2.2 [21] through the PERMANOVA (Permutational Multivariate Analysis of Variance) method and displayed using multiple scaling \u2013 NMDS (Non-Metric Multidimensional Scaling). Visualization of the differences in the fish assemblage was shown through the code designation of individual species (AA \u2013 Alburnus alburnus, AB \u2013 Abramis brama, AN \u2013 Anguilla anguilla, AP \u2013 Alburnoides bipunctatus, AU \u2013 Leuciscus aspius, BB \u2013 Barbus barbus, BJ \u2013 Blicca bjoerkna, CA \u2013 Carassius gibelio, CG \u2013 Cottus gobio, CN \u2013 Chondrostoma nasus, CT\u00a0\u2013 Cobitis taenia, CY \u2013 Cyprinus carpio, EL \u2013 Esox lucius, GA \u2013 Gasterosteus aculeatus, GC \u2013 Gymnocephalus cernua, GG \u2013 Gobio gobio, GL \u2013 Romanogobio albipinnatus, LC \u2013 Squalius cephalus, LG \u2013 Lepomis gibbosus, LI \u2013 Leuciscus idus, LL\u00a0\u2013 Leuciscus Leuciscus, LT \u2013 Lota lota, NB \u2013 Barbatula barbatula, NM \u2013 Neogobius melanostomus, PF \u2013 Perca fluviatilis, PM \u2013 Proterorhinus semilunaris, PP \u2013 Phoxinus phoxinus, PR \u2013 Pseudorasbora parva, RR \u2013 Rutilus rutilus, RS \u2013 Rhodeus amarus, SE \u2013 Scardinius erythrophthalmus, SG \u2013 Silurus glanis, SL \u2013 Sander lucioperca, ST\u00a0\u2013 \u00a0Salmo trutta m. fario, TT \u2013 Tinca tinca, VV \u2013 Vimba vimba). Comparison of\u00a0differences in the juvenile fish assemblage between individual years (2019\u20132021) was\u00a0performed using the Euclidean distance (Jaccard index). The Cao index [22] was used to assess (beta) diversity of\u00a0the\u00a0assemblage between individual sites in the monitored period.<\/p>\n The assemblage of juvenile fish was relatively rich, with 36 species recorded at 22 sites. There were significant differences in the composition of the species community between individual sites; at least four species were recorded per site (Cidlina \u2013 S\u00e1ny in 2019); the most species (15) were caught in 2021 at the Labe\u00a0\u2013 Hradec Kr\u00e1lov\u00e9 site (the section was fished below the weir near the village of Vysok\u00e1 nad Labem). In the monitored period, an average of 9 species were caught at the sites (an average of 7.1 species per site was recorded in 2019, 8.7 in 2020, and 9.7 in 2021). Among the species with the highest abundance were European chub (Squalius cephalus<\/span> \u22116156 ind. [individuum], Fig. 4<\/span>, Tab. 1<\/span>), gudgeon (Gobio gobio<\/span> \u22112976 ind., Fig. 4<\/span><\/em>, Tab. 1<\/span><\/em>), European bitterling (Rhodeus amarus<\/span> \u22112518 ind., Fig. 4<\/span>, Tab. 1<\/span>), common bleak (Alburnus alburnus<\/span> \u22112447 ind., Fig. 4<\/span><\/em>, Tab.\u00a01<\/span><\/em>), common roach (Rutilus rutilus<\/span> \u22112007 ind., Fig. 4<\/span><\/em>, Tab. 1<\/span><\/em>), and barbel (Barbus barbus<\/span> \u22111434 ind., Fig. 4<\/span>, Tab. 1<\/span><\/em>). The Catch Per Unit Effort (CPUE) fluctuated significantly between individual years and sites; the minimum value o\u00a0CPUE was recorded in 2019 at the Berounka in Pilsen (Bukovec) \u2013 0.3 ind.m-1<\/sup> (Fig. 5<\/em>)<\/span>, and the maximum was 25.4 ind.m-1<\/sup> at Ol\u0161e in V\u011b\u0159\u0148ovice in 2021 (Fig. 5<\/em>)<\/span>.<\/span><\/p>\n The\u00a0average value of CPUE between sites and years was 3.3 ind.m-1<\/sup>. A medium and higher CPUE value was recorded in 23 cases during the monitored period\u00a0<\/span>(in 2019 at five sites, and in 2020 and 2021 at nine sites). Similar to CPUE, fish biomass showed high variability between years and sites. The lowest values of\u00a00.4\u00a0g.m-1<\/sup> were recorded in 2019 on the Vltava in Prague (Vran\u00e9, Fig. 6<\/span><\/em>), while the highest values of 5.0 g.m-1<\/sup> were recorded in 2021 on the Odra in Ostrava (Svinov, Fig. 6<\/span>). The average value of biomass between sites in the monitored period reached 1.8 g.m-1<\/sup>. The medium and higher value of biomass was recorded in\u00a027\u00a0cases (in 2019 it was found at seven sites, in 2020 at eight sites, and in 2021 at\u00a012 sites). The ecological status assessment according to the Czech multi-metric index (CZI) showed significant changes in the monitored sites that occurred during 2019\u20132021. Degradation of the status was recorded at four monitored sites compared to previous years (Labe \u2013 Hradec Kr\u00e1lov\u00e9, Plou\u010dnice\u00a0\u2013 D\u011b\u010d\u00edn\/B\u0159eziny, M\u017ee \u2013 Plze\u0148, Dyje \u2013 Podhrad\u00ed, Fig. 7<\/span>). The lowest CZI values, and thus the worst ecological status (i.e., destroyed and damaged), were recorded at\u00a0the following sites: Oh\u0159e \u2013 \u017delina (0.200, Fig. 7<\/span>), Dyje \u2013 Jevi\u0161ovka (0.295, Fig.\u00a07<\/span>), Cidlina \u2013 S\u00e1ny (0.305, Fig.\u00a07<\/span>), and Dyje \u2013 Podhrad\u00ed (0.344, Fig. 7<\/span>). At the Oh\u0159e in \u017delina, the population was mainly dominated by European perch (Perca fluviatilis<\/span>), with a\u00a0minor proportion of common roach and three-spined stickleback (Gasterosteus aculeatus<\/span>). In the community on the Dyje in Jevi\u0161ovka, the majority consisted of western tubenose goby (Proterorhinus semilunaris<\/span>), European bitterling, and common roach. On the Cidlina in S\u00e1ny, the majority share of the community was formed by European bitterling, gudgeon, common roach, and topmouth gudgeon (Pseudorasbora parva<\/span>). On the Dyje in Podhrad\u00ed, European chub, common roach, and European perch dominated the fish community. An\u00a0improvement in ecological status was detected in a total of nine sites (Fig. 7)<\/span>. The most significant improvement during the monitored period was recorded at four sites, i.e., on the Labe in Litom\u011b\u0159ice, Lu\u017enice in Vesel\u00ed nad Lu\u017enic\u00ed, Vltava in Prague (Vran\u00e9), and Dyje in P\u00edse\u010dn\u00e9. At the sites of the Orlice in Nepasice and the Ol\u0161e in V\u011b\u0159\u0148ovice, the ecological status reached first class (i.e., excellent). At the remaining sites, the situation was rather stable \u2013 there was neither significant improvement nor degradation (Fig. 7)<\/span>. Multivariate analyses showed significant differences in the juvenile fish assemblage in 2019\u20132021 (P = 0.011, Fig.\u00a08a<\/span>), but no differences in community diversity across the monitored sites were proven (P = 0.086, Fig. 8b<\/span><\/em>).<\/span><\/p>\n The study was conducted across the Czech Republic. Individual watercourses and sites differed significantly not only in terms of water bearing, geomorphology, but also in the technical modifications of the riverbed. At all 22 monitored sites, the assemblage of juvenile fish was very diverse. Species diversity varied across individual years and sites; a total of 36 species were recorded (a minimum of four and a maximum of 15 species per site). CPUE values showed a relatively high variability between sites and monitored years (Fig. 5). The lowest CPUE values (0.3 ind.m-1<\/sup>, Fig. 5) were recorded on the Berounka in Pilsen in 2019; however, in 2021, CPUE values of 6.8 ind.m-1<\/sup> were recorded (Fig. 5). The highest CPUE values were 25.4 ind.m-1<\/sup> in Ol\u0161e in V\u011b\u0159\u0148ovice in 2021; however, significantly lower abundances were recorded in previous years (4.5 and 2.1 ind.m-1<\/sup>, Fig. 5). Similarly, the biomass also showed great variability in the monitored period between sites and years; the lowest values were found on the Vltava in Prague (0.4 g.m-1<\/sup>, Fig. 6) in 2019, but in 2021 the biomass reached almost double the values (Fig. 6). The highest values of 5.0 g.m-1<\/sup> were in 2021 on the Odra in Ostrava (the Svinov district, Fig. 6); however, more than three times lower biomass values were recorded in previous years (Fig. 6). Significant differences in biomass and CPUE between individual years within the same site may be related to interannual differences, temperature fluctuations or water level fluctuations (floods, drought), which have a significant effect on the reproductive potential of fish and their entire community [6, 24, 25]. Differences in both abundance and biomass can also be influenced by interannual biological cycles, such as the sizes of individual cohorts entering breeding [6, 10], which can vary significantly between individual years. They can also be caused by the fluctuation of available food, i.e., a change in the community of micro and macrozoobenthos, which represents an important source of food for juvenile fish [24, 26, 27]. Among other things, even significant temperature fluctuations have a noticeable effect on fish reproduction [13, 28], because higher water temperatures can\u00a0contribute to an earlier spawning time, while a sudden drop can slow down or delay fish spawning [13, 29]. It can be assumed that a significant drop in temperature in the spring season can also cause the absence of a cohort, especially in fish with batch spawning, such as European chub and common nase. In 2020, February and March were significantly above average in temperature, while May was very cold (with a deviation of -2.1 \u00b0C from normal, [31]). In a number of\u00a0sites, a missing cohort was recorded in a number of sites this year during fish catches, or the size spectrum ranged only in two categories (about 20\u201330\u00a0mm and 40\u201350 mm of body length), and the middle category of 30\u201340 mm was almost absent (this mainly concerned European chub and common nase). Despite significant differences in the abundance of individual species (Fig. 4)<\/span> and significant variability in species diversity (Fig. 8a)<\/span>, and due to significant differences between a number of sites (Fig. 8b)<\/span>, no statistically significant differences were found in the assemblage of juvenile fish between the monitored sites (P = 0.086, Fig. 8b<\/span>); however, this value is quite close to the significance level (P = 0.05). In contract, significant differences in the assemblage were recorded in 2019\u20132021 (P = 0.011, Fig. 8a<\/span>), when the species variability changed noticeably during the monitored years (Fig. 8a)<\/span>. Inconclusive differences in the assemblage of juvenile fish between sites could be caused by a significant representation of eurytopic species, as the monitored sites are more probably to be found in the lower parts of watercourses, and therefore the communities between sites could be quite similar. In contrast, significant differences in the fish community between monitored years may point to fundamental changes that take place during individual years, or reflections of normal interannual fluctuations of an otherwise stable community may have been captured [25]. According to the Czech multi-metric index, two sites almost consistently showed the best composition of the juvenile fish assemblages, i.e. excellent ecological status (0.863\u20131.0 CZI, Fig. 7<\/span>). These were Orlice in Nepasice and Ol\u0161e in V\u011b\u0159\u0148ovice. The banks and riverbed were made of medium coarse gravel to sand. There was a considerable amount of mesohabitats that were suitable both for reproduction and for the growth and survival of the spawning community [32], i.e., river shallows with a low current speed and a significant amount of dead wood, which formed a suitable habitat with enough food and shelter [10, 33]. In\u00a0contrast, the lowest CZI values (0.200, 0.296, 0.305, 0.344, Fig. 7<\/span>), which represent the \u201cworst\u201d state (destroyed to damaged), were found on the Oh\u0159e in \u017delina, the\u00a0Dyje in Jevi\u0161ovka, the Cidlina in S\u00e1ny and the Dyje in Podhrad\u00ed. The\u00a0Oh\u0159e and Dyje were influenced by the adjacent water reservoirs (Nechranick\u00e1, Vranovsk\u00e1, and Novoml\u00fdnsk\u00e1 reservoirs), into which they form the main tributaries. Simultaneously, the reservoirs also influence the resulting assemblage of juvenile fish (e.g., by the height of the swelling and reproduction of part of the reservoir stock in tributaries). In the monitored sections, the riverbed was relatively shallow, stony to sandy and only in places overgrown with algal growths and aquatic macrophytes. On the Oh\u0159e, the species community was relatively poor, with the predominance of European perch in particular, with a smaller occurrence of common roach and three-spined stickleback. In\u00a0the spring, part of the stock travels from the dam to the tributaries, where it reproduces [34, 35]. In the early spring months, perch [35] and then roach [36] reproduce. European perch is able to actively hunt smaller juvenile fish at a size of 25\u201330 mm. It normally grows to this size during July and August [37\u201339]. Its great abundance, together with its enormous predatory potential, allows it to prevail in the assemblage of juvenile fish, where it subsequently forms a dominant share. The low values of the Czech multi-metric index on the Dyje in Podhrad\u00ed and Jevi\u0161ovka were caused by the relatively low abundance of rheophilic species, higher abundance of eurytopic species such as common roach and European bitterling, and especially the presence of non-native species such as western tubenose goby, topmouth gudgeon, and Prussian carp (Carassius gibelio). On the Cidlina in S\u00e1ny, the abundance of gudgeon decreased in the fish community in the given period, and common roach and topmouth gudgeon gradually began to dominate. The community was influenced by the\u00a0proximity of the \u017dehu\u0148sk\u00fd pond, which had an effect on the flow conditions and temperature regime and can also serve as a reservoir for non-native species, such as topmouth gudgeon. According to the CZI, the degradation of\u00a0the ecological status during the monitored three-year period was recorded at four sites (Labe \u2013 Hradec Kr\u00e1lov\u00e9, Plou\u010dnice \u2013 D\u011b\u010d\u00edn\/B\u0159eziny, M\u017ee \u2013 Plze\u0148, and Dyje\u00a0\u2013 Podhrad\u00ed, Fig. 4<\/span>). In the given period, no significant change of mesohabitats was recorded at the monitored sites (e.g., technical modifications of\u00a0the\u00a0riverbed or excessive overgrowth of the riverbed with macrophytes due to low flows). The\u00a0deterioration was mainly caused by the presence of non-native species, which significantly reduce the value of the CZI. These species already expand further from newly colonized areas or are intentionally or unintentionally expanded with fish stocks [40, 41], or escape from ponds and other water bodies (fish production, ornamental ponds and lakes), which are situated in the upper parts of the basin [42]. In contrast, an improvement in the status during 2019\u20132021 was recorded at four sites (Vltava \u2013 Hlubok\u00e1 nad Vltavou, Vltava\u00a0\u2013 Vran\u00e9 nad Vltavou, \u017delivka \u2013 Po\u0159\u00ed\u010d\u00ed, Dyje \u2013 P\u00edse\u010dn\u00e9, Fig. 4<\/span>). The improvement may be related to the creation of suitable mesohabitats for fingerling survival, which\u00a0<\/span>arose as a result of more significant hydrological events (i.e.,\u00a0increased water levels), which were recorded mainly in the spring and autumn months of 2020 (Czech Hydrometeorological Institute, unpublished data). Significant fluctuations in water levels can result in hydromorphological changes in riverbeds [43,\u00a044], especially cleaning of the riverbeds from fine inorganic and organic material (detritus), which can contribute to the creation of\u00a0a\u00a0number of mesohabitats [11]. These can subsequently be used for individual stages of juvenile fish (0+) [32, 45, 46].<\/span><\/p>\n The study results point to the fact that the assemblage of juvenile fish (0+) represents a suitable indicator of the ecological status of our watercourses and is directly and indirectly influenced by the natural conditions in a given year. The\u00a0improvement of the ecological status in many sites was probably caused primarily by increased water levels, which act as an important channel-forming element and which caused the removal of sediments and the creation of\u00a0suitable mesohabitats for the reproduction and subsequent survival of the first stages of juvenile fish (0+), especially in rheophilic species. However, degradation of the ecological status was not caused by a significant change in suitable habitats or their sudden decline, but mainly by the presence of non-native species, which significantly reduce the CZI index value. The conclusions of our survey point to the fact that significant changes in the assemblage of\u00a0juvenile fish can occur at the same site even in a very short period of time (one year). Interannual changes can be very significant, so it is important to carry out monitoring every year in order to be able to separate \u201cnormal\u201d fluctuations from fundamental changes taking place in the assemblage of juvenile fish (0+).<\/span><\/p>\n The Czech version of this article was peer-reviewed, the English version was translated from\u00a0the Czech original by Environmental Translation Ltd.<\/p>\n <\/p>\n","protected":false},"excerpt":{"rendered":" Aquatic organisms have a very good ability to reflect the conditions of the environment they live in and, therefore, they are often used to assess the ecological status of that particular environment. of juvenile fish assemblages (0+) represent an appropriate tool for monitoring the ecological status of watercourses as they show a very rapid response to changes in environmental conditions. The goal of this study was to assess assemblages of juvenile fish (0+) at 22 sites across the Czech Republic between 2019 and 2021.<\/p>\n","protected":false},"author":8,"featured_media":20097,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[86,93],"tags":[3173,3155,795,3172,1928],"coauthors":[3105,3104,3157,324],"class_list":["post-20412","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-hydraulics-hydrology-and-hydrogeology","category-two-articles","tag-assemblages","tag-biomonitoring","tag-ecological-status","tag-juvenile-fish","tag-water-temperature"],"acf":[],"_links":{"self":[{"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/posts\/20412","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/users\/8"}],"replies":[{"embeddable":true,"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/comments?post=20412"}],"version-history":[{"count":8,"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/posts\/20412\/revisions"}],"predecessor-version":[{"id":32078,"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/posts\/20412\/revisions\/32078"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/media\/20097"}],"wp:attachment":[{"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/media?parent=20412"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/categories?post=20412"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/tags?post=20412"},{"taxonomy":"author","embeddable":true,"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/coauthors?post=20412"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}METHODOLOGY<\/h2>\n
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Fig. 1. Monitored watercourses with marked profiles where juvenile fish (0+) were caught:\u00a01) <\/span>Labe \u2013 Hradec Kr\u00e1lov\u00e9, 2<\/span>) Orlice \u2013 Nepasice, 3<\/span>)\u00a0Cidlina \u2013 S\u00e1ny, 4<\/span>) Labe\u00a0\u2013 Litom\u011b\u0159ice, 5<\/span>)\u00a0Plou\u010dnice \u2013 D\u011b\u010d\u00edn (B\u0159eziny), 6<\/span>) Oh\u0159e \u2013 \u017delina, 7<\/span>) Mal\u0161e \u2013 Roudn\u00e9, 8<\/span>)\u00a0Vltava \u2013 Bor\u0161ov, 9<\/span>)\u00a0Vltava \u2013 Hlubok\u00e1 nad Vltavou, 10<\/span>) Lu\u017enice \u2013 Vesel\u00ed nad Lu\u017enic\u00ed, 11<\/span>) M\u017ee \u2013 Plze\u0148, 12<\/span>)\u00a0Berounka \u2013 Plze\u0148, 13<\/span>) S\u00e1zava \u2013 Zru\u010d nad S\u00e1zavou, 14<\/span>) Vltava \u2013 Praha (Vran\u00e9), 15<\/span>)\u00a0\u017delivka \u2013 Po\u0159\u00ed\u010d\u00ed, 16<\/span>) Ostravice \u2013 Ostrava, 17<\/span>) Odra \u2013 Ostrava (Svinov), 18<\/span>)\u00a0Ol\u0161e\u00a0\u2013\u00a0V\u011b\u0159\u0148ovice, 19<\/span>) Morava \u2013 Blatec, 20<\/span>) Moravsk\u00e1 Dyje \u2013 P\u00edse\u010dn\u00e9, 21<\/span>) Dyje \u2013 Podhrad\u00ed, 22<\/span>) Dyje \u2013 Jevi\u0161ovka<\/h6>\n
Catching the fish<\/h3>\n
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Fig 2. Juvenile fish assamblages sampling in shallow sections along the riverbank<\/h6>\n
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Fig. 3. The determination of juvenile fish<\/h6>\n
DATA PROCESSING<\/h2>\n
<\/a>\nRESULTS<\/h2>\n
<\/a>\nFig. 4. The results of juvenile fish survey, abundance of fish species between 2019\u20132021<\/h6>\n
<\/a>\nFig. 5. The results of catch per unit effort (CPUE) at monitored localities between 2019\u20132021<\/h6>\n
Tab 1. Summary of juvenile fish (0+) caught at monitored sites for the period 2019\u20132021<\/h5>\n
<\/a>\n<\/a>\nFig. 6. Biomass of juvenile fish at monitored localities between 2019\u20132021<\/h6>\n
<\/a>\nFig. 7. The evaluation of ecological status using the Czech multimetric index (CZI) at\u00a0monitored localities between 2019\u20132021<\/h6>\n
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<\/a>Fig. 8. Similarities between monitored localities based on juvenile fish assemblages, a) the results of nonmetric multidimensional scaling of juvenile fish assemblages between\u00a02019\u20132021, b) differences in juvenile fish assemblages between localities and across years 2019\u20132021<\/h6>\n<\/a>\nCatch of juvenile fish in a technically heavily modified river basin<\/h6>\n
<\/a>\nThe Oh\u0159e river near the \u017delinsk\u00fd meander<\/h6>\n
<\/a>\n\u00a0Selection of an appropriate flow section depending on the variability of the environment<\/h6>\n
<\/a>\n<\/a>\nAfter determination, the fish were gently released back into the river<\/h6>\n
DISCUSSION<\/h2>\n
CONCLUSION<\/h2>\n