Fish Collections Taken from a Small Agricultural Water Withdrawal Site on the Groot River,Gamtoos River System,South Africa

Summary

Periodic water releases from Beervlei Dam on the Groot River of the Gamtoos River System were planned to flush the riverine pools of brack water and replace the pools with better quality water which was used to flood irrigate lucerne lands. Fish collections were made in a small irrigation canal situated on the banks of the Groot River. Three fish species were collected. Results indicated that up to a total of 131 smallscale redfin minnows, Pseudobarbus asper, are removed from the system every five minutes at this one small water withdrawal site. Larger minnow specimens and carp, Cyprinus carpio, were entrained during high river flows. When the river flow was reduced there were higher catches of young of the year fish. The fish are carried with the pumped water, which is flood irrigated onto lucerne fields, resulting in stranding and eventual mortality. It is recommended that the use of suitable screens, such as wedge-wire screens, could reduce the number of fish removed from the system during these irrigation periods.     

Light,temperature and flow regimes of the Vaal River at Balkfontein,South Africa

A detailed investigation into light, temperature and flow regimes of the Vaal River was done for the first time. The Vaal River is ecologically and economically one of the most important rivers in South Africa. In a South African context, the Vaal River, with an average Secchi disk depth (Z _sd) of 0.41 m and an average euphotic zone depth (Z _eu) of 1.3 m, is a moderately turbid system. Red light (approx. 670 nm) penetrated Vaal River water to a greater degree than other components of the light spectrum. Water temperature in the Vaal River (min. = 10, max. = 27 °C at midday), closely followed seasonal changes in average atmospheric temperatures. The water-column shows little temperature stratification. The Vaal River is a highly regulated system with relatively high discharge rates at Balkfontein (average 112 m³ s^–1), but relatively low current velocity (approx. 0.35 m s^–1). Discharge was the most important variable to influence transparency of Vaal River water. Higher discharge resulted in higher total suspended solids (TSS) concentration and higher extinction coefficient (k) values as well as in higher turbidity and thus in lower Z _eu and Z _sd. From the mean TSS (141 mg l^–1) it was calculated that the Vaal River (mean annual run-off of 3532 million m³) transported 498016 tonnes of suspended solids per annum.     

Longitudinal movement of fish in response to a single-day flow pulse

We studied whether fish were displaced longitudinally downstream by a 1-day whitewater kayaking pulse flow release from Camino Dam on Silver Creek, a tributary of the South Fork American River, California. On 15 September 2004 flows were increased from a base flow of 0.48 m³·s^-1 to a peak of 18.48 m³·s^-1 by midday, and decreased back to base levels. Rainbow trout (Oncorhynchus mykiss) and brown trout (Salmo trutta) were observed in snorkel surveys before and after the pulse. Counts of young-of-the-year and juvenile trout were 26% and 9% lower after the pulse, respectively. Counts of adult trout were 12% higher. Six adult trout were radio-tagged and were observed in the reach before, during, and after the pulsed flow. Our results suggest that most trout were able to remain in the study reach during the pulse, but that smaller fish may be more likely to be displaced downstream.     

Metal contamination and human health risk associated with the consumption of Labeo rosae from the Olifants River system,South Africa

The Olifants River, a tributary of the Limpopo River system, is one of the most polluted rivers in South Africa. In May 2011 the concentrations of metals in fish muscle tissue from two impoundments, Loskop and Flag Boshielo dams, on the Olifants River were measured and a human health risk assessment conducted to investigate whether it was safe to consume Labeo rosae from these impoundments. Labeo rosae is one of the most common pan fish in these impoundments and is readily available to rural communities. Metals are accumulating in the muscle tissue of L. rosae even although the fish populations appear to be healthy. At Loskop Dam all L. rosae analysed exceeded the recommended hazard quotient (HQ) of 1 for antimony, and less than 50% exceeded that for lead. At Flag Boshielo Dam, the recommended HQ was exceeded for lead in less than 50% of L. rosae analysed, and more than 50% exceeded that for antimony. The weekly consumption of 150?g of L. rosae muscle tissue from these impoundments may pose an unacceptable health risk to rural communities.     

Influences of dams with different levels of river connectivity on the fish community structure along a tropical river in Southeastern Brazil

The influence of three types of dams with different degrees of river connectivity on the structure of fish communities along the Paraíba do Sul River was studied: total blockage (Dam 1); partial blockage allowed by a permanent lateral channel (Dam 2); and total blockage, but with a mechanism operating in the summer for fish passage (Dam 3). The tested hypothesis is that the degree of river connectivity influences the fish community. The largest differences in fish fauna were expected between the reservoir and downriver stretch in Dam 1 with total blockage; an intermediate difference in Dam 3 with total blockage but with a fish passage; and the least difference in Dam 2 with partial blockage. Fish were caught by gill nets between January and March 2010 and between January and February 2011 (wet seasons) in two zones: the reservoir and the downriver stretch from the dam. A total of 43 fish species was recorded, including eight non‐native and two marine species. The 13 most abundant species (n > 100; frequency of occurrence >20%) occurred in all three stretches of the river. The community structure changed significantly between the reservoir and associated downriver stretch, with higher richness downriver compared to the reservoir zone. A trend for higher occurrence of migratory fishes (e.g. Pimelodus maculatus, Pimelodus fur, Leporinus copelandii and Prochilodus lineatus) was found in the downriver zone, suggesting the influence of dams on their upriver migration. The predictions were not fully matched. Although the most significant difference in the fish community structure between the reservoir and the downriver was found for Dam 1, the partial blockage in Dam 2 showed broader differences in the fish fauna than the total blockage in Dam 3 with the fish ladder, which may indicate that the latter is not a guarantee that species and genetic flux will be interchanged, since the water velocity may be a constraint to upriver fish migration.     

Health and chemical burdens of fish species from polluted and hyper-eutrophic freshwater ecosystems in South Africa

Three aquatic ecosystems in South Africa, the Hartbeespoort, Klipvoor and Bospoort Dams, are classified as hyper-eutrophic, because of high nutrient loads and chemical pollution. Water and two fish species, Clarias gariepinus and Cyprinus carpio, were collected from these dams to assess the impact of eutrophication and chemical pollutants on their health status. Water and muscle samples were analysed for organic and inorganic chemicals. Condition factor was determined and a necropsy performed to note any macroscopic abnormalities. A histology-based fish health assessment was done on the liver, kidney, gills and gonads. A number of fish from the three dams exhibited livers with fatty change and focal discoloration, skin lesions and parasites within the visceral cavity. The prevalence and severity of histopathology in the liver resulted in higher liver index values than the index values for kidneys and gills. Aluminium, silicon and chromium were detected in the water and muscle tissue. The DDT metabolite p,p’-DDE was present in both species, as well as in fish from the reference site, Marico-Bosveld Dam. Only C. gariepinus from Hartbeespoort Dam had p,p’-DDD levels higher than 5 µg g^?1 per edible portion. Water from hyper-eutrophic dams adversely affects the health of freshwater fish.     

Bioaccumulation of selected metals in the gill,liver and muscle tissue of rednose labeo Labeo rosae from two impoundments on the Olifants River,Limpopo river system,South Africa

Metal concentrations in the gill, muscle and liver tissues of Labeo rosae from two impoundments, Loskop and Flag Boshielo dams on the Olifants River, were evaluated in 2011 to detect patterns in metal associations between tissues and impoundments. Elevated concentrations of Ba, Zn, B, Al, Si and Fe, relative to a pristine site in the catchment, were found in the muscle, liver and gill tissues at both impoundments. Molybdenum concentrations were exceptionally high in all tissues at Loskop Dam and in liver at Flag Boshielo Dam. No definite pattern in the ratio metal concentrations within, or between, fish tissues was identified. The expected trend, liver > gills > muscle, was found at both impoundments, but was less prominent at Loskop Dam. Metal concentrations in muscle of Loskop Dam fish were significantly higher than in those at Flag Boshielo Dam. The inverse was true for liver. The long-term impact of elevated metal concentrations on fish health at both impoundments raises concern.     

The effects of river barriers and range expansion of the population genetic structure and stability in Greenside Darter (Etheostoma blennioides) populations

The genetic structure of a stream-dwelling fish, the Greenside Darter, Etheostoma blennioides, is described from variation at nine microsatellite loci in 26 populations in the northern-most portions of the species’ range in southern Ontario, Canada in two sampling years. We found relatively high levels of genetic structure at the among- and within-watershed scales, with some watersheds and populations exhibiting very high divergence. The Ausable River populations were especially isolated, containing distinct populations of potential conservation concern. Temporal replicates at selected localities showed evidence of substantial temporal variation in genetic structure, perhaps resulting from movement among sites. We found strong evidence for an effect of river barriers (dams and weirs) on dispersal measured by genotype assignment techniques. However, we found no bias in upstream vs downstream dispersal. Significant isolation-by-distance relationships in both sample years indicate that river distance is an important factor regulating gene flow in these watersheds. The Canadian Greenside Darter populations are expanding their range into more northerly watersheds, but also show substantial within-watershed genetic structure despite substantial dispersal.     

Variation in the significant environmental factors affecting larval abundance of four major Chinese carp species: fish spawning response to the Three Gorges Dam

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Population structure and genetic diversity of trout (<Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>) above and below natural and man-made barriers in the Russian River,California

The effects of landscape features on gene flow in threatened and endangered species play an important role in influencing the genetic structure of populations. We examined genetic variation of trout in the species Oncorhynchus mykiss at 22 microsatellite loci from 20 sites in the Russian River basin in central California. We assessed relative patterns of genetic structure and variation in fish from above and below both natural (waterfalls) and man-made (dams) barriers. Additionally, we compared sites sampled in the Russian River with sites from 16 other coastal watersheds in California. Genetic variation among the 20 sites sampled within the Russian River was significantly partitioned into six groups above natural barriers and one group consisting of all below barrier and above dam sites. Although the below-barrier sites showed moderate gene flow, we found some support for sub-population differentiation of individual tributaries in the watershed. Genetic variation at all below-barrier sites was high compared to above-barrier sites. Fish above dams were similar to those from below-barrier sites and had similar levels of genetic diversity, indicating they have not been isolated very long from below-barrier populations. Population samples from above natural barriers were highly divergent, with large F _st values, and had significantly lower genetic diversity, indicating relatively small population sizes. The origins of populations above natural barriers could not be ascertained by comparing microsatellite diversity to other California rivers. Finally, below-barrier sites farther inland were more genetically differentiated from other watersheds than below-barrier sites nearer the river’s mouth.     

Phylogeography and the genetic structure of the land-locked freshwater prawn Macrobrachium asperulum (Crustacea: Decapoda: Palaemonidae) in Taiwan

Millions of fish ascend through fishways in South America every year, but there is no evidence that downstream passage is occurring in large dams. Based on this concern, this study monitored the fish ladder at Lajeado Dam, Tocantins River, a large Amazonian tributary. To investigate the extent of downstream movements through the fishway, ascending and descending movements were quantified between November 2007 and October 2008. Monitoring showed that the ladder is restrictive to many species in both directions, but downstream passage was much more limited: almost all fish captured in the ladder (99.5%) were ascending the facility. Consequently, the numerical ratio between ascending and descending fish (ind./m²) showed high positive values throughout the year (1508:1 on average); migratory species showed higher ratios. All results showed that downstream passage through the ladder is very limited, and that the facility allows only one-way movements (i.e., upstream). This is the first empirical evidence showing that a ladder is critically deficient for downstream passage of fishes in South America.     

Occurrence of oestrogenic pollutants and widespread feminisation of male tilapia in peri-urban dams in Bulawayo,Zimbabwe

Peri-urban water bodies are at risk from excessive pollution as they are direct sinks for urban effluents. The occurrence of oestrogenic and androgenic endocrine disrupting chemicals (EDCs) in effluents and water bodies around the city of Bulawayo, Zimbabwe, and their effects on wild fish was investigated in 2013. Effluent and water were sampled from sewage treatment plants, an urban stream, and effluent-polluted dams, and were compared with a ‘pristine’ dam upstream of Bulawayo. Organic pollutants were extracted by solid-phase extraction and tested for EDCs using a yeast oestrogen/androgen screen. Oestrogenic and androgenic potencies were expressed as 17β-oestradiol equivalent (EEq) or dihydrotestosterone equivalent (TEq). Tilapia and catfish from the dams were analysed for gonado-somatic indices and testis histopathology. Effluents from STPs, which directly flow into Umguza Dam, had EEq of 33 ng l^?1 and 55 ng l^?1, respectively. Umguza Dam, Khami Dam and Matsheumhlope Stream had EEqs of 237 ng l^–1, 9 ng l^?1 and 2 ng l^?1, respectively. Androgenic activity was detected in only one STP (TEq = 93 ng l^?1). Tilapia sampled from effluent-polluted dams had high incidences of testis-ova, but catfish had no signs of reproductive dysfunction. These findings underscore the need for greater attention to EDCs in developing countries where there is scant literature regarding their occurrence and impacts.     

Changes in abundance of larvae of the four domestic Chinese carps in the middle reach of the Yangtze River, China, before and after closing of the Three Gorges Dam

The four domestic Chinese carps, i.e. grass carp (Ctenopharyngodon idella), black carp (Mylopharyngodon piceus), silver carp (Hypophthalmichthys molitrix) and bighead carp (Hypophthalmichthys nobilis), cast their drifting eggs in the running water of the Yangtze River. In 1997 ~ 2005, a systematic study on the dynamics of the abundance the larvae of the four domestic Chinese carps was performed in the middle reach of the Yangtze River, close to Sanzhou city. It was calculated that in breeding seasons from early May to late June every year the abundance of fry drifting through the section of Sanzhou was 3.59 billion in 1997, 2.75 billion in 1998, 2.15 billion in 1999, 2.85 billion in 2000, 1.90 billion in 2001, 1.90 billion in 2002, 406 million in 2003, 339 million in 2004 and 105 million in 2005 respectively. Several environmental parameters related to the dynamics of larval abundance were also examined simultaneously. The construction of the Three Gorges Dam near Yichang between the upper and middle reaches of the Yangtze River has apparently had a drastic influence on the abundance of fish larvae.     

Biochemical genetic variation between four populations of Labeobarbus polylepis from three river systems in South Africa

The genetic variation within four Labeobarbus polylepis populations from both river and dam environments in the Limpopo, Incomati and Phongolo River systems was studied. Gene products of 22 enzyme-coding loci were resolved using horizontal starch gel electrophoresis. Fourteen (64%) of the 22 loci were monoallelic in all populations. Levels of polymorphism (P_0.95) ranged between 9.1% and 22.7%. The heterozygosity varied from 0.028 for the Westoe Dam population (Phongolo River system) to 0.093 in the Spekboom River population (Limpopo River system). The genetic distance, F_ST and N_EM values, as well as pair-wise contingency χ² analyses indicate a lack of gene flow between populations, as expected for isolated fish. Evidence of foreign genetic material in one population was also observed.     

Spatial extent of analysis influences observed patterns of population genetic structure in a widespread darter species (Percidae)

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Establishment of the non-native fish Metynnis lippincottianus (Cope 1870) (Characiformes: Serrasalmidae) in lower São Francisco River,northeastern Brazil

Alterations in the hydrologic regime downstream from hydroelectric dams create a high invasibility to non-native species. This study aims to analyze the establishment of non-native Metynnis lippincottianus downstream of the Xingó Dam, lower São Francisco River, Brazil. Adults in reproduction were found throughout the study. Gonadosomatic index was higher in the reproductive phases and the species produces a large number of small oocytes. Hydrometric level and water flow data after the construction of Xingó Dam showed decrease in both parameters, facilitating the establishment of M. lippincottianus. Management actions are suggested to reduce the threat on the native biota.     

小型水坝梯级开发对永宁河流域鱼类多样性的影响

永宁河是长江上游右岸的一级支流,其干、支流上共建有20余座小型水坝。为探究梯级水电站对鱼类多样性的影响,在永宁河流域设置共42个采样点,覆盖干支流及各个水坝,分别于2018年7月、10月和2019年1月、4月进行了四次鱼类资源调查。调查期间通过刺网、地笼、电捕等方法共采集到鱼类69种7332尾,隶属于4目13科54属,其中有长江上游特有鱼类13种,列入《中国脊椎动物红色名录》濒危和易危鱼类3种,国家二级重点保护鱼类岩原鲤(Procypris rabaudi)1种。Pinkas相对重要性指数(IRI)值较大主要为宽鳍鱲(Zacco platypus)、鲫(Carassius auratus)乐山小鳔鮈(Microphysogobio kiatingensis)等小型鱼类,29种鱼类的IRI值小于10;平均全长＜10cm的鱼类有24种3620尾,平均体重＜50g的鱼类有47种6493尾,鱼类规格较小,小型化严重。永宁河干流下游种类最多,多样性最高,干流中游鱼类数量最多。受自然环境以及水坝等的影响,永宁河的鱼类分布具有明显的空间差异。水坝类型对鱼类多样性有显著影响;而季节对鱼类多样性影响不显著。无水坝阻隔河段鱼类多样性著高于低头坝和高头坝阻隔河段;夏季的短距离洄游鱼类种数显著高于冬季和春季,但由于数量较少对鱼类多样性的季节性变化影响不明显。各种结果表明水坝阻隔对永宁河鱼类多样性和时空分布存在明显影响,为保护受小型水电站影响河流的鱼类多样性,有必要修复重要鱼类栖息地,适当拆除部分小型水坝,并科学开展增殖放流。     

The impact of small physical obstacles on upstream movements of six species of fish

In the course of the `Meuse Salmon 2000' programme, most weirs and dams (3–8 m in height) in the regulated River Meuse have been progressively equipped with new fishways in order to restore the free circulation of all amphibiotic fish species. Nevertheless, fish entering into major spawning tributaries are still confronted with various kinds of physical obstacles of which the overall impact on fish migration has never been investigated. In order to test their ability to negotiate physical obstacles, 128 individuals of fish (Salmo trutta, Thymallus thymallus, Salmo salar, Chondrostoma nasus, Barbus barbus and Esox lucius) were captured several weeks before their spawning migrations and tagged with radio-transmitters. They were tracked from 30 to 466 days in the River Ourthe and six spawning tributaries over the period October 1995 to June 2001. All obstacles recorded in this study have been classified according to their type and main characteristics (i.e. slope, length and height). Results indicated that most fish migrate during or outside the spawning period and that some small obstacles are not as insignificant as initially thought and can significantly disrupt and/or obstruct their upstream movements. There is a need to harmonize interests in the sustainable conservation of fish populations and the development of small-scale hydropower generation and tourism.     

Disturbance of the indigenous gene pool of the threatened brook lamprey Lethenteron sp. S by intraspecific introgression and habitat fragmentation

Artificial introduction and habitat fragmentation affect the indigenous gene pools of fluvial animals. To investigate the effect of human activities on the genetic population structure of vulnerable brook lamprey Lethenteron sp. S in a single river system, samples from 12 tributaries of the Jinzu River, Japan, were analyzed using mitochondrial and microsatellite DNA markers. Exogenous Lake Biwa (Japan) haplotypes and alleles were detected in lampreys from several Jinzu River tributaries. Since Lake Biwa is the source of the commercial ayu fish Plecoglossus altivelis that is introduced in the Jinzu River, the exogenous Lake Biwa lamprey genotypes in the Jinzu River probably originated from the Lake Biwa lampreys that were unintentionally introduced along with the ayu fish. Bayesian admixture and mitochondrial DNA analyses revealed various genetic disturbance phases of the exogenous genotypes in the Jinzu River, such as the six indigenous populations, four admixed populations with low frequencies (average admixture proportion = 0.02–0.04; exogenous haplotype proportion <0.01), one introgressed population (0.71 and 0.57) and one population almost displaced by exogenous genotypes (0.93 and 0.96). Samples from three tributaries with weirs were genetically differentiated from the others by using pairwise F _ST and Bayesian analyses; the results suggested isolation by the weirs. Reduced mitochondrial DNA diversity was observed in 1 of the 3 samples probably due to reduced population size. These findings indicate that the indigenous lamprey populations in the Jinzu River are seriously affected by introgression with exogenous genotypes via unintentional introduction and habitat fragmentation by weirs.     

大藤峡大坝蓄水对浔江鱼类群落的影响

2017年7月至2021年2月对浔江鱼类资源进行调查（每月调查一次）,以定制刺网、虾笼和钓钩为主要作业网具,结合相对重要性指数、鱼类丰度生物量比较（ABC）曲线、相似性分析、非度量多维尺度分析、生态网络和零模型等分析方法,探讨广西大藤峡大坝蓄水对浔江鱼类群落的影响。调查期间共采集鱼类77种,隶属7目19科63属。卷口鱼（Ptychidio jordani）、赤眼鳟（Squaliobarbus curriculus）、鲤（Cyprinus carpio）、粗唇鮠（Leiocassis crassilabris）的相对重要性指数（IRI）值为850.59-2347.23,表明它们是浔江优势种。大藤峡大坝蓄水后浔江鱼类群落发生了一系列变化：（1）鱼类群落相似性聚类分析显示,各年度间鱼类群落相似度均大于59.73%,总体呈现出时间相隔越远群落相似性越低的趋势。此外,鱼类种类数由69种下降为51种;（2）浔江鱼类群落受干扰程度随着时间的推移而增加,鱼类丰度生物量比较曲线（ABC曲线） W值由0.052降至-0.004。此外,基于浔江鱼类所构建的生态网络集散节点数不断减少,结构趋向于简单化,生态网络稳定性减弱;（3）基于时间生态位研究结果表明鱼类种间竞争加剧,时间生态位重叠增幅最大的种对是罗非鱼sp-东方墨头鱼以及卷口鱼-鲫等生态习性相近鱼类。（4）基于时间生态位重叠指数构建的零模型结果揭示了浔江鱼类群落构建取决于环境因素,大坝蓄水后浔江鱼类群落向竞争主导的随机分布发展格局转变。综上所述,大藤峡大坝蓄水对浔江鱼类群落产生较大的影响,亟需采取相应的保护措施。研究为后续浔江鱼类资源的保护和恢复工作以及大藤峡大坝运行的建议提供理论基础。