Spatiotemporal Variation in Fish Assemblage Structure in Tropical Floodplain Creeks

Biotic assemblages of aquatic floodplain systems have great potential to randomly reshuffle during annual flood periods, and have been described both as stochastically and deterministically assembled. However, only a limited number of studies have been conducted in relatively few habitat types. To evaluate large-bodied fish assemblage structure of floodplain creeks, we used experimental gill nets to sample fishes at sites spaced at even intervals within three creeks in consecutive dry seasons. A total of 60 species were collected, 41 of which were collected both years. The most frequently collected species were piscivores and algivores/detritivores. Multivariate analysis suggested non-random patterns of assemblage structure in both years. Correspondence analysis (CA) of the species abundance-by-site matrix for 2001 suggests species assemblages were most similar among sites within the same creek regardless of depth or longitudinal position. Discriminant function analysis (DFA) correctly predicted 100% of samples based on creek identity, and species ordination scores revealed creek-specific species subsets. In 2002, CA and DFA did not distinguish creeks based on species assemblages. Instead, we observed a significant positive relationship between assemblage composition and site depth and position along the creek longitudinal gradient. Assemblages were most similar among sites of comparable depth and longitudinal position, regardless of creek identity. Predators occurred almost exclusively at mouth and mid-reach sites. Flood duration prior to our 2002 sampling period was prolonged due to abnormally heavy rainfall in November and December 2001 (typically the falling-water period), and may account for the observed inter-annual variation in fish assemblage structure.     

长江中游草鱼天然种群的生化遗传结构及变异

采用淀粉或聚丙烯酰胺凝胶电泳方法分析了长江中游武汉江段草鱼天然种群(n=81)中10种同工酶约28个基因座位的遗传变异型。该种群的多态座位比例为16.7%,平均杂合度为0.0739。而Utter和Folmar(1978)曾报道美国的5个草鱼人工繁殖种群的多态座位比例及平均杂合度分别为6%和0.021。比较结果表明,近交很可能是导致草鱼人工繁殖种群中遗传变异性降低的主要原因。我们认为生产上采用数量大、来源广的亲鱼进行人工繁殖,并定期用天然种群更换或补充繁殖用亲鱼很可能是保持或增加鱼类人工繁殖种群遗传变异性的一种有效手段。     

Alien Fishes in Natural Streams: Fish Distribution, Assemblage Structure, and Conservation in the Cosumnes River, California, U.S.A.

The Cosumnes River is the largest stream without a major dam on its mainstem in the Sacramento–San Joaquin drainage, central California, U.S.A. We studied its fishes over a 3-year period to answer the following questions: (1) Was the native fish fauna still present? (2) Why were alien fishes so abundant in a river system with a 'natural' flow regime, which elsewhere has been shown to favor native fishes? (3) Were there assemblages of fishes that reflected environmental differences created by the underlying geology? (4) Were there features of the watershed that consistently favored native fishes or that could be managed to favor native fishes? Of the 25 species collected, 17 were alien species; 14 species (five native) were abundant or widely distributed enough to use in detailed analyses. Of the native species, only rainbow trout, Oncorhynchus mykiss, still occupied much of its native range in headwater streams. Other native species have been extirpated or persisted mainly above barriers to alien invasions. The most widely distributed alien species was redeye bass, Micropterus coosae, previously unknown from the river, whose abundance was associated with low-numbers of native species. Other aliens were found primarily in low-land habitats on the valley floor or foothills. Canonical Correspondence Analysis indicated that both native and alien species located on environmental gradients determined largely by elevation, temperature, flow, and emergent vegetation, but the associations with these variables were not strong. While most alien fishes were found in lowland sections of river flowing through agricultural regions, the general relationships between species abundance and landscape-level variables were weak. Assemblages of fishes were poorly defined mixtures of native and alien species. The strikingly distinct geological regions of the basin no longer supported distinct fish assemblages. Species distributions were highly individualistic, reflecting dynamic patterns of introductions, invasions, and local extinctions, as well as physiological tolerances and life history patterns. Most native fishes are likely to persist in the Cosumnes River only if summer flows are increased and if populations above natural barriers are protected from further invasions by alien species, especially redeye bass. General conclusions from this study include: (1) altered habitats can support native species under some circumstances; (2) new fish assemblages with characteristics of 'natural' communities are likely to develop in invaded systems; (3) restoring flow regimes to favor native fishes may require restoring minimum summer flows as well as high channel-forming flows. However, reversing or even reducing, the impact of the predatory redeye bass, pre-adapted for California streams, is probably not possible.     

Stability of the Wabash River fish assemblages from 1974 to 1998

1. We measured temporal variability of the fish assemblage in the Wabash River using a 25‐year electrofishing dataset through a combination of a time‐lag analysis and multivariate analysis. 2. The fish assemblage had substantial year‐to‐year variation, but the overall abundance pattern did not change. Based on time‐lag analyses and ordinations, there was only weak predictable directional change at individual sites. At the scale of the entire reach, however, the overall combined data had a statistically significant directionality with the time‐lag analysis. 3. These results support the hypothesis that the middle Wabash River stream fish assemblage has undergone change over a time period of 25 years, although at the scale of individual sites this change was not detectable.     

Development and Application of a Predictive Model of Freshwater Fish Assemblage Composition to Evaluate River Health in Eastern Australia

Multivariate predictive models are widely used tools for assessment of aquatic ecosystem health and models have been successfully developed for the prediction and assessment of aquatic macroinvertebrates, diatoms, local stream habitat features and fish. We evaluated the ability of a modelling method based on the River InVertebrate Prediction and Classification System (RIVPACS) to accurately predict freshwater fish assemblage composition and assess aquatic ecosystem health in rivers and streams of south-eastern Queensland, Australia. The predictive model was developed, validated and tested in a region of comparatively high environmental variability due to the unpredictable nature of rainfall and river discharge. The model was concluded to provide sufficiently accurate and precise predictions of species composition and was sensitive enough to distinguish test sites impacted by several common types of human disturbance (particularly impacts associated with catchment land use and associated local riparian, in-stream habitat and water quality degradation). The total number of fish species available for prediction was low in comparison to similar applications of multivariate predictive models based on other indicator groups, yet the accuracy and precision of our model was comparable to outcomes from such studies. In addition, our model developed for sites sampled on one occasion and in one season only (winter), was able to accurately predict fish assemblage composition at sites sampled during other seasons and years, provided that they were not subject to unusually extreme environmental conditions (e.g. extended periods of low flow that restricted fish movement or resulted in habitat desiccation and local fish extinctions).     

Taxonomic Composition and Trophic Structure of the Continental Bony Fish Assemblage from the Early Late Cretaceous of Southeastern Morocco

The mid-Cretaceous vertebrate assemblage from south-eastern Morocco is one of the most diversified continental vertebrate assemblages of this time worldwide. The bony fish component (coelacanths, lungfishes and ray-finned fishes) is represented by relatively complete specimens and, mostly, by fragmentary elements scattered along 250 kilometres of outcrops. Here we revisit the bony fish assemblage by studying both isolated remains collected during several fieldtrips and more complete material kept in public collections. The assemblage comprises several lungfish taxa, with the first mention of the occurrence of Arganodus tiguidiensis, and possibly two mawsoniid coelacanths. A large bichir cf. Bawitius, is recorded and corresponds to cranial elements initially referred to ‘Stromerichthys’ from coeval deposits in Egypt. The ginglymodians were diversified with a large ‘Lepidotes’ plus two obaichthyids and a gar. We confirm here that this gar belongs to a genus distinctive from Recent gars, contrary to what was suggested recently. Teleosteans comprise a poorly known ichthyodectiform, a notopterid, a probable osteoglossomorph and a large tselfatiiform, whose cranial anatomy is detailed. The body size and trophic level for each taxon are estimated on the basis of comparison with extant closely related taxa. We plotted the average body size versus average trophic level for the Kem Kem assemblage, together with extant marine and freshwater assemblages. The Kem Kem assemblage is characterized by taxa of proportionally large body size, and by a higher average trophic level than the trophic level of the extant compared freshwater ecosystems, but lower than for the extant marine ecosystems. These results should be regarded with caution because they rest on a reconstructed assemblage known mostly by fragmentary remains. They reinforce, however, the ecological oddities already noticed for this mid-Cretaceous vertebrate ecosystem in North Africa.     

The Influence of Selected Environmental Variables on Fish Assemblage Structure in a Range of Southeast African Estuaries

This study compared the ichthyofaunal assemblages in 10 Eastern Cape Province, South Africa, estuaries to identify whether there were any structural variations between the assemblages and to determine the environmental and physical factors linked to these variations. Species belonging to both the marine migrant and estuarine resident groups, by consistent representation within each estuary grouping, were responsible for the separation of fish assemblage structures between the different types of systems. The data further revealed that fish assemblages in the three main types of estuaries investigated were distinct, linked primarily to estuary mouth status and estuary size.     

大川河鱼类区系及其群落生态结构的研究

鱼类区系及其群落生态结构,在理论和实践上都有十分重要的意义。但是,关于鱼类区系的生态结构问题,还未见详细报道。本文通过对大川河鱼类区系及其群落生态结构的分析,探讨鱼类区系及其群落生态结构的规律。     

Effects of harvest and length limits on shovelnose sturgeon in the upper Wabash River, Indiana

Shovelnose sturgeon Scaphirhynchus platorynchus are one of the few sturgeon species that currently support sustainable commercial harvest. However, harvest closures for many Eurasian sturgeons have resulted in increased exploitation of this fishery, thereby raising concerns about the sustainability of shovelnose sturgeon resources. As a result, the maintenance of self‐sustaining shovelnose sturgeon populations will require the estimation of appropriate harvest levels. This study used an age‐structured population model to examine the effects of harvest (u = 0.15–0.75) and length restrictions on population abundance, mean length‐at‐harvest, biomass, yield, and reproductive potential of female shovelnose sturgeon in the upper Wabash River, Indiana. Model simulations for four hypothetical length‐restriction scenarios (610‐ to 813‐mm reverse slot limit, and a 610‐, 635‐, and 660‐mm minimum length limit) were compared to outputs with no restriction. All population parameters within each length‐restriction scenario declined with increases in harvest level. For each harvest level, all population parameters increased as length limits became more restrictive. The reverse slot limit and 610‐mm minimum length limit provided adequate protection to allow population parameters to increase through an annual harvest level of 0.55. However, these length restrictions were not sufficiently conservative to warrant implementation due to their similarity to length‐at‐maturity of female shovelnose sturgeon. The implementation of a 635‐mm minimum length limit would protect female shovelnose sturgeon from harvest rates >0.75, allow 92% of the females to remain available for harvest, and minimize short‐term (<30 years) declines in yield. Further, sensitivity and robustness analyses suggested that the 635‐mm minimum length limit would allow population parameters to increase even at the worst‐case scenario. As a result, the 635‐mm minimum length limit was recommended as the most appropriate regulation to promote conservation and sustainable harvest of shovelnose sturgeon in the upper Wabash River.     

Influence of Approach Velocity and Mesh Size on the Entrainment and Contact of a Lowland River Fish Assemblage at a Screened Irrigation Pump

Fish screens can help prevent the entrainment or injury of fish at irrigation diversions, but only when designed appropriately. Design criteria cannot simply be transferred between sites or pump systems and need to be developed using an evidence-based approach with the needs of local species in mind. Laboratory testing is typically used to quantify fish responses at intake screens, but often limits the number of species that can studied and creates artificial conditions not directly applicable to screens in the wild. In this study a field-based approach was used to assess the appropriateness of different screen design attributes for the protection of a lowland river fish assemblage at an experimental irrigation pump. Direct netting of entrained fish was used along with sonar technology to quantify the probability of screen contact for a Murray-Darling Basin (Australia) fish species. Two approach velocities (0.1 and 0.5 m.sec⁻¹) and different sizes of woven mesh (5, 10 and 20 mm) were evaluated. Smaller fish (<150 mm) in the assemblage were significantly more susceptible to entrainment and screen contact, especially at higher approach velocities. Mesh size appeared to have little impact on screen contact and entrainment, suggesting that approach velocity rather than mesh size is likely to be the primary consideration when developing screens. Until the effects of screen contacts on injury and survival of these species are better understood, it is recommended that approach velocities not exceed 0.1 m.sec⁻¹ when the desire is to protect the largest range of species and size classes for lowland river fish assemblages in the Murray-Darling Basin. The field method tested proved to be a useful approach that could compliment laboratory studies to refine fish screen design and facilitate field validation.     

Strain Variation in Mycobacteriummarinum Fish Isolates

A molecular characterization of two Mycobacterium marinum genes, 16S rRNA and hsp65, was carried out with a total of 21 isolates from various species of fish from both marine and freshwater environments of Israel, Europe, and the Far East. The nucleotide sequences of both genes revealed that all M. marinum isolates from fish in Israel belonged to two different strains, one infecting marine (cultured and wild) fish and the other infecting freshwater (cultured) fish. A restriction enzyme map based on the nucleotide sequences of both genes confirmed the divergence of the Israeli marine isolates from the freshwater isolates and differentiated the Israeli isolates from the foreign isolates, with the exception of one of three Greek isolates from marine fish which was identical to the Israeli marine isolates. The second isolate from Greece exhibited a single base alteration in the 16S rRNA sequence, whereas the third isolate was most likely a new Mycobacterium species. Isolates from Denmark and Thailand shared high sequence homology to complete identity with reference strain ATCC 927. Combined analysis of the two gene sequences increased the detection of intraspecific variations and was thus of importance in studying the taxonomy and epidemiology of this aquatic pathogen. Whether the Israeli M. marinum strain infecting marine fish is endemic to the Red Sea and found extremely susceptible hosts in the exotic species imported for aquaculture or rather was accidentally introduced with occasional imports of fingerlings from the Mediterranean Sea could not be determined.     

Temporal and spatial variation in an index of biological integrity for the middle Wabash River, Indiana

Few studies have addressed within-year temporal variation of IBI scores. We compared index of biotic integrity (IBI) scores for two summer sampling events from a large river during 25 annual periods. The results indicated that IBI scores calculated from June samples were not significantly different from July samples. Spatial autocorrelation was present, such that sites that were closer together produced similar IBI scores and could not be considered independent. Temporal autocorrelation was present, but was not strong. Lower quality sites (low IBI score) did not have higher variation than higher quality sites. Our results show that a single sample of fishes by boat electrofisher during the summer in a large river such as the Wabash River can produce a repeatable estimate of IBI score. Thus, repeated or additional sampling within the summer season to improve the quality of the evaluation is not warranted. Handling editor: J. Trexler     

Invasive Silver Carp movement patterns in the predominantly free-flowing Wabash River (Indiana,USA)

Many organisms must move among habitats to fulfill life history requirements. Fish movements have been widely studied and tend to be either fine-scale (i.e., routine) and governed by factors such as food availability and cover, or broad-scale and associated with spawning migrations. However, movements of invasive fishes in non-native ecosystems are comparatively poorly understood despite the often critical importance of fish movement and dispersal for invasion success. We examined invasive Silver Carp (Hypophthalmichthys molitrix) movements using acoustic telemetry to monitor the timing, distance, and direction of fish movements and assessed movements in relation to seasonal, annual, environmental, and individual factors in the Wabash River (Indiana, USA), a largely unregulated Midwestern river. Silver Carp exhibited highly variable movements that could be rapid and large in magnitude; however, tagged individuals remained stationary most of the time. Despite high variability, several trends emerged, indicating the importance of backwater habitats, avoidance of small tributaries, and tendencies of tagged fish to exhibit directed spring and fall broad-scale movements. Summer movements were smaller in magnitude, characterized by lower movement rates, and evenly split between upstream and downstream directions, although tagged Silver Carp moved more frequently during summer months. Our results indicate that specific seasons (i.e., spring and early fall) and locations (i.e., backwaters) are likely targets for Silver Carp control in the Wabash River and should also be useful targets for early detection and control in other largely unconstrained rivers over a broad geographic range (e.g., Great Lakes tributaries and upper Mississippi River mainstem and tributaries).     

Food Webs in Relation to Variation in the Environment and Species Assemblage: A Multivariate Approach

The abiotic environment has strong influences on the growth, survival, behavior, and ecology of aquatic organisms. Biotic interactions and species life histories interact with abiotic factors to structure the food web. One measure of food-web structure is food-chain length. Several hypotheses predict a linear relationship between one environmental variable (e.g., disturbance or ecosystem size) and food-chain length. However, many abiotic and biotic variables interact in diverse ways to structure a community, and may affect other measures of food web structure besides food-chain length. This study took a multivariate approach to test the influence of several important environmental variables on four food-web characteristics measured in nine ponds along a hydroperiod gradient over two years. This approach allowed for testing the ecosystem size and dynamic constraints hypotheses while in context of other possibly interacting environmental variables. The relationship between amphibian and invertebrate communities and pond habitat variables was assessed to understand the underlying food-web structure. Hydroperiod and pond area had a strong influence on amphibian and invertebrate communities, trophic diversity and δ¹⁵N range. The range in δ¹³C values responded strongly to dissolved oxygen. Food-chain length responded to multiple environmental variables. Invertebrate and amphibian communities were structured by pond hydroperiod which in turn influenced the trophic diversity of the food web. The results of this study suggest food-chain length is influenced by environmental variation and species assemblage and that a multivariate approach may allow us to better understand the dynamics within and across aquatic food webs.     

金沙江中游圆口铜鱼早期资源现状

2010年6月至7月在金沙江中游攀枝花格里坪金沙滩(26°35°28.96″N,101°31°52.01″E)设置同定采样断面,开展了金沙江中游圆口铜鱼早期资源现状的调查.结果表明,金沙江中游有金安桥、朵美、皮拉海、灰拉古、观音岩5个圆口铜鱼产卵场,产卵总量为3078.2万粒.圆口铜鱼的产卵行为和产卵量受江水的温度、流量、涨落水持续时间等多个因素的影响.调查期间圆口铜鱼的产卵初始时间为6月7日,盛期在6月下旬至7月上旬.近几年来,圆口铜鱼的产卵规模呈现出逐年下降的趋势,产卵场的位置也有所改变.通过了解金沙江中游江段圆口铜鱼早期资源分布状况,为金沙江中游圆口铜鱼资源保护提供了基础资料.     

长江中下游褶纹冠蚌10个群体CO I基因序列变异分析

以线粒体CO I基因为分子标记,对长江中下游褶纹冠蚌(Cristaria plicata)10个群体共200个个体的遗传多样性进行了研究.获得了620 bp的同源序列,A+T的平均含量为60.1%,明显高于G+C含量(39.9%),有105个核苷酸变异位点,占全部碱基数的17%,转换和颠换之比达到8.7,检测到了58个单倍型(GenBank登录号:EU698893～EU698950),Hap-5是主体单倍型,占总个体数的41%.褶纹冠蚌鄱阳湖群体(PY)平均核苷酸差异数和核苷酸多样性指数均最高,分别为25.426和0.041 01,太湖群体(TH)和衢州群体(QZ)遗传多样性参数较低.基于群体间遗传距离构建的NJ系统树中,洪泽湖内的3个群体与巢湖群体首先聚为一支,然后与由钱塘江群体、太湖群体、衙州群体和洪湖群体聚成的分支聚在一起,而后与洞庭湖群体聚在一起,最外侧一支为鄱阳湖群体.分子方差分析(AMOVA)得出群体间的遗传分化指数(Fst)为0.208 1(P<0.001),说明我国褶纹冠蚌不同群体间存在一定的遗传分化.     

Characteristics of the Summer Hydrological Regimen and Chlorophyll Distribution in the Volga River Reservoirs

Field observations on chlorophyll content and hydrological parameters such as temperature, dissolved oxygen and conductivity profiles, Secchi disk transparency and water color were carried out at 5 reservoirs of the Mid and Lower Volga River during August 1990 and 1991. Principal Component Analysis distinguished four classes from 46 sampling points based on the hydrological regimen and phytoplankton development.     

Intraindividual and Interspecies Variation in the 5S rDNA of Coregonid Fish

This study was designed to characterize further the nontranscribed intergenic spacers (NTSs) of the 5S rRNA genes of fish and evaluate this marker as a tool for comparative studies. Two members of the closely related North American Great Lakes cisco species complex (Coregonus artedi and C. zenithicus) were chosen for comparison. Fluorescence in situ hybridization found the ciscoes to have a single multicopy 5S locus located in a C band-positive region of the largest submetacentric chromosome. The entire NTS was amplified from the two species by polymerase chain reaction with oligonucleotide primers anchored in the conserved 5S coding region. Complete sequences were determined for 25 clones from four individuals representing two discrete NTS length variants. Sequence analysis found the length variants to result from presence of a 130-bp direct repeat. No two sequences from a single fish were identical. Examination of sequence from the coding region revealed two types of 5S genes in addition to pseudogenes. This suggests the presence of both somatic and germline (oocyte) forms of the 5S gene in the genome of Coregonus. The amount of variation present among NTS sequences indicates that accumulation of variation (mutation) is greater in this multicopy gene than is gene conversion (homogenization). The high level of sequence variation makes the 5S NTS an inappropriate DNA sequence for comparisons of closely related taxa. Received: 22 August 1997 / Accepted: 31 October 1997