Avoidance of oxygen-poor zones by fish in the Elbe River

For three selected weeks in July, August, and October 1985, catches from anchor net vessels at ten stations along the tidal Elbe River (northern Germany) were analyzed and related to oxygen conditions in the river. The oxygen concentrations decreased from an average of 6.6 ml/L in the estuary to an average of 1.4 mg/L upstream. Fish were found to be concentrated downstream from the low-oxygen zone and at the entrance to a shallow side arm of the main stream. Highest catches of eel were made where oxygen levels were in the range of 1.2–3 mg/L, highest catches of flounder at 3–4 mg/L, and highest catches of juvenile and adult smelt in areas with more than 5 mgO₂/L. Such a situation enables fishermen to make extraordinarily high catches. It is concluded that despite high levels of toxicants, the tidal Elbe still offers living conditions adequate for the mass of fish species as long as there is a sufficient supply of oxygen.     

Larval fish production in the tidal River Elbe 1985–1986

In 1985 and 1986 ichthyoplankton composition was studied during seven sampling series at 37 stations along the tidal Elbe and its tributary rivers between Hamburg harbour and the North Sea. The highest larval density was observed in May and April. No, or very few, larvae occurred from late summer to early spring. Smelt (59% on average of all samples) and twaite shad (20%) dominate in the freshwater region. Herring/sprat (17%) dominate in the estuary. All major spawning grounds are located along the southern shore. Smelt spawn further upstream 1 month earlier than twaite shad. Three percent of all larvae found were flounder. Most of them occurred upstream from the estuary in the R. Este and in other tributary rivers. It is not clear whether flounders are able to spawn in freshwater. Attention is drawn to the fact that an unknown but probably very high percentage of the ichthyoplankton is entrained by local power plants.     

Sub-population structure of common fish species in the Elbe River estimated from DNA analysis

The aim of this study was to analyse the genetic structure of populations for seven common cyprinid fish species within a 120‐km‐long stretch of the lowland Elbe River, northern Germany. The results are needed for habitat modelling to estimate the proportion that environmentally based variance has of the total variances of home range, species distribution, habitat use and fish assemblage structure. Polymerase chain reaction (PCR)‐fingerprinting offers a rapid, efficient method for generating genetic markers and was therefore used to obtain an overview on population‐genetic structures of the following seven fish species: asp (Aspius aspius), bleak (Alburnus alburnus), blue bream (Abramis ballerus), common bream (Abramis brama), gudgeon (Gobio gobio), ide (Leuciscus idus) and roach (Rutilus rutilus). Of the 20 random primers, between eight (ide) and 18 (roach) produced polymorphic bands. The mean levels of genetic similarity between samples, estimated as bandsharing frequencies, varied between 76% in bleak and 98% in asp. The corresponding genetic distances among samples varied between 0.02 ± 0.01 in asp and 0.24 ± 0.09 in bleak. The genetic distances among samples were not significant in all of the pairwise comparisons, and correlated only weakly with the geographic distances among sampling sites. It was therefore concluded that the stretch of the Elbe surveyed was inhabited by single, panmictic populations of the species studied and thus that the observed habitat preferences, fish distribution, home range and ecological performance of species within this area will depend on stochastic environmental factors or result from biotic interactions.     

Distribution of fish in the Virgin River,a tributary of the lower Colorado River

Synopsis The Virgin River, a major tributary of the lower Colorado River, contains a unique, though impoverished, native ichthyofauna (six species) that is largely intact despite the introduction of exotic fishes (13 species) and alterations of the river. The main conclusions of the study are: (1) The longitudinal distribution pattern of the native species does not follow theoretical expectations of a downstream increase in species richness; (2) for the size of the basin (>15,000 km²), the native ichthyofauna is extremely depauperate; and (3) most of the exotic fish are not established in the river, but persist through repeated invasions from downstream reservoirs.     

Abundance and distribution of fish in the lower Mnembo River, Malawi-Mozambique

Endorheic Lake Chilwa is one of the most productive lakes for fisheries in Africa. High human population densities and agricultural practices in the Chilwa catchment have been linked to observed declines of the annual fish catch in the lake. The Mnembo River is a major inflow into Lake Chilwa which has received little scientific study to date. In 2003/2004, fish diversity, abundance and distribution were monitored monthly at three sites in the Mnembo River. Twelve fish species were collected, a subset of the fourteen fish species present in Lake Chilwa. Although Barbus spp. were the most abundant species sampled in the Mnembo, total biomass was higher for Labeo cylindricus (6709 and 10,434 g, respectively). Total biomass of Pareutropius longifilis (1741 g) and Brycinus imberi (1174 g) were also high in the river. Catches of Barbus and Labeo were highly correlated (r = 0.763). Compared with other inflows into Lake Chilwa (Likangala and Domasi), the Mnembo River appears to be less adversely influenced by human populations, with high abundance of Barbus and strong presence of the riverine species Labeo, Pareutropius and Brycinus.     

Karyological and gonadal sex of eels(Anguilla anguilla) from the German Bight and the lower River Elbe

Yellow eels(Anguilla anguilla) taken during summer from random commercial trapnet samples in the littoral area of Helgoland (n=116) and from a freshwater area of the River Elbe near Hamburg (n=109) were examined with regard to their karyological (i.e. existence of female sex chromosomes) and gonadal sex. In 47 % and 21 % of the two samples, respectively, chromosomes were unidentifiable because of insufficient numbers of mitotic plates. All eels from Helgoland, except one phenotypically undetermined fish, exhibited female gonads: 48 had female sex chromosomes and 13 were karyologically males. As found previously in the River Elbe, eels with male gonads predominated (n=55); 25 were undifferentiated. Of the gonadal males 26 were karyological males and 16 karyological females; the rest could not be identified by chromosome patterns. In contrast, all but one of the Elbe eels with female gonads (n=28) had female sex chromosomes. Some aspects of the sex reversal documented in the eel are considered.     

The ammonia-oxidizing nitrifying population of the River Elbe estuary

Abstract: The ammonia-oxidizing bacterial population of the tidal River Elbe was analysed. In the freshwater section of the river, abundance was generally at a magnitude of 10⁴ cells per g dry weight and 10³ cells per ml in sediments and in water samples, respectively. In the brackish water region, counts decreased drastically with the increase in salinity caused by the low level of abundance of ammonia-oxidizers in the seawater. The contribution of attached ammonia-oxidizers to the total number ranged between 50 and approximately 100%, depending on the respective load with suspended particulate matter (SPM) of the water. The presence of seven distinct species of the genus Nitrosomonas was established by DNA hybridizations. Based on 16S rRNA gene partial sequence analyses, four groups, comprising phylogenetically closely related species, were defined. Dependence of ammonia oxidation on the NH₄Cl concentration, tolerance against increasing salinity and the possession of urease activity were found to be useful ecophysiological characteristics, being in accordance with phylogenetic relationships among the species.     

Environmental factors as forces structuring the fish community of the Elbe Estuary

Smelt, flounder, eel, three-spined stickleback, twaite shad, ruffe and herring were the major species among 62 forming the fish community of the Elbe estuary. Species richness, species diversity, evenness and total fish biomass decreased in the upstream direction. Total abundance was greatest during summer. Salinity was the most significant physico-chemical factor affecting species richness and total fish biomass, whereas water temperature was the best predictor of total abundance. Marine fish species decreased with decreasing salinity, while the freshwater species roach and ide were absent at salinities > 15‰. Bream, blue bream, white bream, perch and pikeperch occurred more frequently in shallow marginal regions with lower current velocities, while herring and other marine species occurred closer to the deep central regions with high current velocities. Annual and seasonal variations of the community structure mainly reflected in population dynamics of smelt, flounder, twaite shad, three-spined stickleback and eel, especially those of 0-age smelt. Populations of smelt and ruffe and their importance in the fish community increased between 1989 and 1992, while those of twaite shad and eel decreased. At oxygen concentrations <3 mg I¹, smelt and flounder were rare, but eels were at their maximum at 3.5 mg I⁻¹. Changes of species composition and fish abundance were closely related to daytime and tidal cycle.     

Hydrological seasonality dictates fish fauna of the lower Araguaia River,Tocantins-Araguaia basin

Hydrological seasonality of flow dictates diversity in tropical aquatic ecosystems. Large tropical rivers and tributaries are typically more depth and shows increased flow velocity and area in flood than in dry season. A thorough analysis of seasonality effect on fish community structure can provide valuable information of major forces driving tropical communities. However, these types of analyses have been limited by poor knowledge of tropical diversity, human impacts on environment, and biased sampling methods. We used a pristine large tropical river (and tributaries) and five types (12 gill nets, beach seine nets, longlines, branch baited hooks, and cast nets) of fishing gears to present an evaluation of flow seasonality effect on fish community. We sampled fourteen sites in river channel and tributaries in the lower Araguaia River. Sampling was conducted in flood (March and May 2009) and dry (July and September 2009) seasons of a typical seasonal year. Species richness, Shannon Diversity and Evenness, mean similarity of binary data, and abundance (CPUE) were analyzed by PERMANOVA and PCoA. We also analyzed the species most correlated (by Spearman correlation rank) with flood and dry season. Features differed significantly between flood and dry seasons, but not between channel and tributaries. The composition and abundance of community, and the representative species of flood and dry changed quite along the year. Flood showed lotic-related species, and dry presented lentic-related species. Thus, we achieved an alternation of fish community between season, both for channel and tributaries.     

乌江下游干流鱼类物种多样性及其资源保护

为摸清乌江下游干流现有的鱼类种类组成和物种多样性状况, 探索水电开发对鱼类群落多样性的影响, 本研究于银盘电站蓄水前的2006-2008年和蓄水后的2011-2013年, 采用渔获物调查方法对乌江下游沿河至白马干流江段鱼类进行了调查。两次调查共采集鱼类105种, 其中2006-2008年采集到100种, 2011-2013年采集到62种; 两次调查相比, 广适性鱼类减少10.38%, 湖沼定居型鱼类减少0.98%, 喜流水性鱼类减少9.62%。两个时期的鱼类群落多样性分析显示: 各个调查江段Margalef丰富度指数(R)和Shannon-Wiener多样性指数(H)在2011-2013年均低于2006-2008年。渔获物分析结果表明: 大鳍鳠(Mystus macropterus)、中华倒刺鲃(Spinibarbus sinensis)、瓣结鱼(Tor (Folifer) brevifilis)等鱼类在渔获物中的重量比例从2006-2008年间的大于5%, 下降到2011-2013年间的不足2%, 而(Hemiculter leucisculus)、草鱼(Ctenopharyngodon idellus)、黄颡鱼(Pelteobagrus fulvidraco)等在2011-2013年渔获物中的重量比例有所上升, 成为调查区域的主要渔获对象。丰度生物量比较表明: 2006-2008年鱼类群落结构受到中等程度的干扰, 而2011-2013年受到严重程度的干扰。为保护乌江下游的鱼类生物多样性, 需采取现有栖息地修复、控制过度捕捞等多种资源保护方式。     

An assessment of the fish population of the lower reaches of the Sanyati River,Zimbabwe

The fish population of the lower reaches of the Sanyati River was studied using multifilament gillnets and monthly sampling was conducted over 13 consecutive months. A total of 15 fish species belonging to seven families were collected and variations in monthly catches and catch per unit effort and condition were observed. The five most common species exhibited a seasonal breeding pattern, with most breeding occurring in the rainy season. The exotic Nile tilapia Oreochromis niloticus was found to have established itself in the Sanyati River. The results of this study were compared with those of previous workers on Lake Kariba.     

Transport of Algal Cells in Hyporheic Sediments of the River Elbe (Germany)

The advective transport of algal cells into the interstices of the hyporheic zone of the River Elbe was spatially and temporally heterogenous. Even deep sediment layers were reached by large phytoplankton species. Therefore, it is suggested that (i) the advective interstitial transport patterns vary between different algal sizes and morphotypes and (ii) sediment characteristics, expressed by the permeability coefficient k_f of porous media, affect retention and retardation of surface water algae during subsurface transport. The transport behaviour of different green algae (Chlorella sp., Scenedesmus acuminatus, Desmodesmus communis, and Pediastrum duplex) and algal sized microspheres was tested in flow‐through column experiments with hyporheic sediments. The algal cell transport was directly related to the permeability of the column sediments. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Length-weight and length-length relationships of three fish species from the lower Yalong River,China

Length-weight relationships (LWRs) and length-length relationships (LLRs) were evaluated for three endemic fish species sampled from the lower Yalong River and its biggest tributary (the Anning River), in China. Specimens were captured using set gillnet (mesh size 4 cm) and backpack electro-fishing (power output 400 W, depth fished 1 m, area covered 3 m²) from June to July 2018. LWRs and LLRs are presented for the following species (Sinogastromyzon sichangensis, Micropercops swinhonis and Percocypris pingi).     

Metal-binding proteins in bream (Abramis brama L.) caught in the River Elbe

Metal-binding proteins were investigated in livers of bream caught in the River Elbe from Steti (Czech Republic) to Hamburg (Federal Republic of Germany). A major zinc and copper binding protein fraction with a low molecular weight of 10 000 to 12 000 Da and with properties similar to mammalian hepatic metallothionein was isolated from bream livers using gel filtration chromatography. Two protein isoforms could be separated by reversed phase-high performance liquid chromatography (RP-HPLC), however, mercury was associated with only one isoform. The possibility of different detoxification potentials of the isoforms is discussed. Maximal concentrations of metal-binding protein were detected in samples from Dresden. If metal-binding proteins are to be included in a biological monitoring study, further investigations are required.     

Observations of the Suspended Matter Distribution Dynamics in the Elbe Estuary from Time Series Aerial Photographs

Series of aerial photographs taken with an interval of 6 Minutes were used to study the dynamics of the suspended matter distribution in a 1 km section of the Elbe Estuary. The observations show heterogeneous distribution patterns which are different at each phase of the tidal cycle. The comparison with the bathymetry indicates that the distribution is mainly a function of the river bed topography, which modifies the local current structure. The surface distribution in the fairway region is especially determined by the ship traffic.     

Mineralization of 4-sulfophthalate by aPseudomonas strain isolated from the River Elbe

The bacteriumPseudomonas sp. strain RW31 isolated from the river Elbe utilized the ammonium salt of 4-sulfophthalate (4SPA) as sole source of carbon, sulfur, nitrogen, and energy and grew also with phthalate (PA) and several other aromatic compounds as sole carbon and energy source. The xenobiotic sulfo group of 4SPA was eliminated as sulfite, which transiently accumulated in the culture supernatant up to about 10 µM and was slowly oxidized to the stoichiometrical amount of sulfate. Biodegradation routes of 4SPA as well as of PA converged into the protocatechuate pathway and from found activities for the decarboxylation of 4,5-dihydroxyphthalate we deduce this compound the first rearomaticized intermediate after initial dioxygenation. Protocatechuate then underwentmeta-cleavage mediated by a protocatechuate 4,5-dioxygenase activity which was competitively inhibited by the structurally related compound 3,4,5-trihydroxybenzoate; protocatechuate accumulated in the medium up to an about 2 mM concentration. Indications for the presence of selective transport systems are presented.     

DNA barcoding reveals the temporal community composition of drifting fish eggs in the lower Hongshui River,China

Determining the temporal community composition of fish eggs in particular regions and understanding the reproductive times of regional fish taxa are key aspects of the management and regulation of regional fish stocks. However, it is extremely difficult to accurately identify fish eggs due to the absence of diagnostic morphological characters. We sampled fish eggs in the lower Hongshuihe River (an upper mainstem of the Pearl River) between May and September 2020. We then used DNA barcoding to determine the species composition of the egg pool and to predict the spawning periods of the identified species. A total of 641 eggs and 17 larvae were chosen for molecular identification; 397 eggs and 17 larvae yielded high‐quality barcoding sequences. The high failure rate (~38%) was most likely due to long‐term storage in low concentrations of ethanol prior to molecular analysis. We successfully classified 392 eggs into 10 species and 13 larvae into four species using public databases. Most of the species identified in the egg pool were small and/or benthic, and migratory species were rare. This may partially reflect the adverse effects of hydropower cascade development in this river section. We also found that spawning periods tended to be species‐specific. Our study provides a reference for the conservation and management of regional fishery stocks.     

Metal-binding proteins in bream (Abramis brama L.) caught in the River Elbe

Metal-binding proteins were investigated in livers of bream caught in the River Elbe from Steti (Czech Republic) to Hamburg (Federal Republic of Germany). A major zinc and copper binding protein fraction with a low molecular weight of 10 000 to 12 000 Da and with properties similar to mammalian hepatic metallothionein was isolated from bream livers using gel filtration chromatography. Two protein isoforms could be separated by reversed phase-high performance liquid chromatography (RP-HPLC), however, mercury was associated with only one isoform. The possibility of different detoxification potentials of the isoforms is discussed. Maximal concentrations of metal-binding protein were detected in samples from Dresden. If metal-binding proteins are to be included in a biological monitoring study, further investigations are required.     

长江下游近口段近岸鱼类群落多样性及潮汐强度的影响

为了解长江下游近口段近岸鱼类群落多样性及其潮汐的影响,于2016—2017年在靖江样点、2017—2018年在常熟样点分别进行连续4个季度的鱼类调查,同步收集潮汐强度数据。结果表明:靖江样点共监测到鱼类61种,隶属于9目18科47属,鲢(Hypophthalmichthys molitrix)、刀鲚(Coilia nasus)、贝氏?(Hemiculter bleekeri)、草鱼(Ctenopharyngodon idellus)、鳙(Aristichthys nobilis)为主要优势种;常熟样点共监测到鱼类41种,隶属于8目14科34属,鲢、中国花鲈(Lateolabrax maculatus)、鳙、鳊(Parabramis pekinensis)和鲫(Carassius auratus)为主要优势种;靖江样点Margalef指数、Shannon指数和Simpson指数均大于常熟样点,Pielou指数则小于常熟样点; SIMPER分析表明,靖江和常熟样点周年群落组成平均相似度分别为64.5%和64.7%,样点间平均相异度为61.1%;不同季节各潮汐周期内鱼类群落多样性相关分析结果...     

Changes of fish assemblages after construction of an estuary barrage in the lower Nakdong River,South Korea

In the Nakdong River, an estuary barrage was constructed in 1987, and it divided the freshwater and the seawater, resulting in a change in the ecosystem. To estimate the impact of barrage construction on fish assemblages, we evaluated 20 years of monitoring data before and after the construction of the estuary barrage, and evaluated the role of fishways. The barrage construction generated entire changes of fish assemblages. After construction, the number of fish species dropped sharply, and 36 species disappeared. Conversely, 18 species appeared at this site, including eight freshwater species, seven of which were exotic or translocated species. Barrage construction affected freshwater fish more severely than it did estuarine and marine species because of the existence of an estuarine environment below the barrage. We did not detect any evidence of recovery of fish assemblages. A total of 31 species were collected at fishways, and the number of individuals collected at each fishway was positively correlated with the amount of discharge from the estuary barrage, mean daily tide level, and water temperature. Migratory fish using a fishway had obvious occurrence periods. Therefore, the efficiency of fishway use can be increased if an appropriate management plan is prepared and implemented.