Freshwater Areas Research Articles

Point sampling the abundance of European eel (Anguilla anguilla) in freshwater areas

The European eel population is in decline. Urgent management actions are required. To monitor their effect, we developed a fast sampling method, applicable in shallow rivers and tributaries. We compared the Carle & Strub estimator from 35 double pass electric fishing samples with Point Abundance Sampling by Electrofishing or PASE (24 point samples on average by section) which we adapted for the eel. The correlation between both methods was highly significant (r2=94%, p<0.001) for densities lower than 150 eels .100 m-2. PASE, being a cheaper sampling method, thus constitutes an efficient and cost-effective method for evaluating management actions and further biological studies.

Taura syndrome virus (TSV) in Thailand and its relationship to TSV in China and the Americas

The cultivation of exotic Penaeus vannamei in Thailand began on a very limited scale in the late 1990s, but a Thai government ban on the cultivation of P. monodon in freshwater areas in 2000 led many Thai shrimp farmers to shift to cultivation of P. vannamei. Alarmed by the possibility of Taura syndrome virus (TSV) introduction, the Thai Department of Fisheries required that imported stocks of P. vannamei be certified free of TSV by RT-PCR (Reverse Trasciption Polymerase Chain Reaction) testing. During the interval of allowed importation, over 150,000 broodstock shrimp were imported, 67% of these from China and Taiwan. Despite the safeguards, TSV outbreaks occurred and we confirmed the first outbreak by RT-PCR in early 2003. This resulted in a governmental ban on all shrimp broodstock imports from February 2003, but TSV outbreaks have continued, possibly due to original introductions or to the continued illegal importation of stocks. To determine the origin of the TSV in Thailand, the viral coat protein gene VP1 was amplified by RT-PCR from several shrimp specimens found positive for TSV by RT-PCR from January to November 2003. These included 7 samples from P. vannamei disease outbreaks in Thailand, 3 other non-diseased shrimp samples from Thailand and Burma and 6 samples including P. vannamei and P. japonicus from China. Comparison revealed that the Thai, Burmese and Chinese TSV types formed a clade distinct from a clade of TSV types from the Americas.

Instream distributions and feeding habits of two species of sleeper, Eleotris acanthopoma and Eleotris fusca, in the Teima River, Okinawa Island

The instream distributions and feeding habits of two species of sleeper, Eleotris acanthopoma and E. fusca, were studied in the Teima River on Okinawa Island, southern Japan. Both adult fishes inhabited the river, but their distribution patterns were found to be different. The distribution of E. acanthopoma was from the tidally influenced area to the lower part of the freshwater area, whereas E. fusca was distributed almost entirely in the freshwater area. They were found to coexist at the upper limit of the tidally influenced area and the lower part of the freshwater area. Their feeding habits were clearly different, although both species were carnivorous. Eleotris acanthopoma fed mainly on crabs in the tidally influenced area and on aquatic snails in the freshwater area, where they coexist with E. fusca. In contrast, E. fusca fed mainly on shrimps in the freshwater area. Their coexistence may result from the difference in their feeding habits.

SETTLEMENT AND UPSTREAM MIGRATION FOR JAPANESE MITTEN CRAB AND FUNCTION OF SESERAGI-FISHWAY IN NAGARA ESTUARY BARRAGE

Settlement and upstream migration in the Japanese mitten crab (Eriocheir japonica) was investigated in the Seseragi-fishway in the Nagara estuary barrage. Megalopa larvae settled and metamorphosed to crab stage in the upper tidal zone in the Seseragi-fishway. The youngest crabs were nearly two millimeters in carapace width. After attaining a minimum of four millimeters, the crabs began to migrate upstream and reach the freshwater area. Settlement of megalopa larvae occurred mainly in early summer (June) and early winter (December). Their upstream migration to the freshwater area began in July and August. The majority of larvae that settled in winter did not survive and metamorphose to the crab stage due to low water temperatures. Thus, the growth and upstream migration of the Japanese mitten crab seemed to be strongly influenced by water temperature in the estuary. This mode of settlement with two peaks in summer and early winter reflected the temporal pattern of reproduction observed in the sea. In this study, it is clarified that the Seseragi-fishway have a function of settlement and upstream migration for supplement of decreased estuary zone. With respect to engineering works in estuaries such as the Seseragi-fishway, it is recommended that we take into account the processes of settlement and migration of young crabs.

Cytogenetic Characterization of &lt;I&gt;Anopheles sundaicus&lt;/I&gt; (Diptera: Culicidae) Population from Car Nicobar Island, India

In India, Anopheles sundaicus is now found abundantly and widely only in the Andaman and Nicobar islands, where this species is the sole malaria vector. Recent studies in Thailand and Indonesia have established An. sundaicus as a complex of three isomorphic species (species A, B, and C) identifiable on the basis of cytological variations together with enzyme polymorphism analysis. A study was conducted to examine cytologically An. sundaicus from Car Nicobar island, district Nicobar, India. More than 300 samples screened for ovarian polytene chromosomes had X chromosome of Xa type as reported in case of species A and chromosome arm (2b) similar to that in species C. This combination suggests the existence of a new cytogenetic variant, i.e., cytotype D, in the Indian subcontinent that has not been reported so far. Examination of male and female mitotic karyotypes further substantiated these results. Only cytotype D was prevalent in the fresh water and brackish water areas of the island, indicating wider adaptability of this form to different habitats.

Survival rate and growth performance of Cyprinus carpio L. in intensively cultivated rice fields

In the freshwater area of Vietnam's Mekong Delta, Barbodes gonionotus (Bleeker), Cyprinus carpio L. and Oreochromis niloticus (L.) are often reared together in rice fields. The survival rate and specific growth rate (SGR) of C. carpio showed a large variance. To understand the underlying reasons for this variation, we used multiple regressions for the variables SGR and survival rate, using the results of eight experiments in such polycultures at the Co Do rice–fish experimental station. The SGR of C. carpio declined with increasing rice density. Interspecific competition with O. niloticus also had a negative effect on C. carpio SGR. When fertilizer or manure is added to the trench of the rice–fish field or when extra food can be given to the fish, O. niloticus seems more appropriate than C. carpio. The survival rate of C. carpio depended on season, C. carpio stocking weight and density and the biomass of wild fish species. To obtain higher survival rates, one should stock fewer fish but of a larger size, after thorough eradication of wild fish species.

Demographic attributes of yellow-phase American eels (Anguilla rostrata) in the Hudson River estuary

Management of American eels (Anguilla rostrata) requires an understanding of how demographic attributes vary within large estuaries. Yellow-phase American eel length and age structure, growth, dispersal, nematode infestation rates, loss rate (natural mortality and emigration), and production were measured at six sites throughout the tidal portion of the Hudson River. Short-term dispersal was low, with &gt;70% of eels at all sites captured &lt;1 km from their original tagging area. Length was similar among sites (total length = 45.7 ± 0.3 cm), whereas age was substantially lower for brackish-water sites (8 ± 4 years) than for freshwater sites (17 ± 4 years). Growth was higher for brackish-water sites than for freshwater sites (8.0 cm·year–1 and 3.4 cm·year–1, respectively). From 1997 to 2000, infestation by the exotic nematode Anguillicola crassus increased dramatically in mean intensity as well as prevalence. Annual loss rates measured for the six sites varied between 9% and 24%, with no statistical difference between freshwater and brackish-water sites. Estimated eel production was higher in a brackish-water habitat (1.10–1.77 kg·ha–1·year–1) than in a freshwater location (0.21–0.58 kg·ha–1·year–1). The results of this study support a recent proposal to establish freshwater areas as exploitation reserves.

Vegetation ecology of the pans (playas) of Soetdoring Nature Reserve, Free State Province

A comparison of the vegetation of two pans (playas) inside Soetdoring Nature Reserve, a freshwater and a brackish pan, is presented. These ephemeral pan communities are also compared to the vegetation of the hot spring and two permanently inundated earth dams inside the brackish pan's basin. The vegetation of the freshwater communities differs significantly from that of the brackish pan itself. The freshwater pan was classified as a Mixed Grass Pan and the brackish pan as an Open Diplachne Pan. The Mixed Grass Pan is characterised by a Cynodon transvaalensis – Gnaphalium declinatum community, associated with the following sub- communities: Selago dinteri – Cynodon transvaalensis , Panicum schinzii – Cynodon transvaalensis and Portulaca oleracea – Cynodon dactylon subcommunity. Cynodon transvaalensis is the dominant species in this pan. The Open Diplachne Pan is characterised by a Diplachne fusca – Eragrostis bicolor community with a Diplachne fusca subcommunity and an Eragrostis bicolor – Diplachne fusca subcommunity associated with it. Diplachne fusca is dominant in the pan basin. A TWINSPAN classification, refined by Braun-Blanquet procedures, revealed five distinct plant communities for the pan basins and freshwater areas inside the basin collectively. This information is important since very few published analyses are available for pans in the Free State Province, as well as in South Africa as a whole.

From Rio via The Hague to Johannesburg: the role of multi-stakeholder dialogues

The Stakeholder Forum will contribute a number of partnership initiatives in the areas of food security, freshwater, energy and health. These will demonstrate that stakeholders, working in partnership, can play their roles and meet their responsibilities in delivering sustainable development agreements.

Timing and Location of Wing Molt in Horned, Red-necked and Western Grebes in North America

Abstract We document timing and location of wing molt in the Horned Grebe (Podiceps auritus), Red-necked Grebe (Podiceps grisegena), and Western Grebe (Aechmophorus occidentalis). Horned Grebes left breeding ponds in late May to August and were observed on large ponds and lakes (near breeding locations) where they replaced remiges before progressing to wintering areas in September and October. Red-necked Grebes moved to much larger bodies of water such as the Great Lakes and the coast following breeding and prior to molt. On the Pacific Coast, Boundary Bay, British Columbia was identified as a major molt site. Freshwater molting areas were identified around Manitoulin Island in northern Lake Huron. On the Atlantic coast, molt sites were located in the Gulf of St. Lawrence. Western Grebes were found in wing molt at both large freshwater lakes and coastal locations (including Boundary Bay, British Columbia). Like the Great Crested Grebe (P. cristatus) and Eared Grebe (P. nigricollis), Horned, Red-necked and...

Characteristics of Na +-dependent respiratory chain in Vibrio anguillarum, a fish pathogen, in comparison with other marine Vibrios

The activity of membrane-bound NADH oxidase of Vibrio anguillarum M93 (serotype J-O-1), which causes vibriosis in freshwater area was activated by Na + in the same manner as other marine Vibrios. However, in addition to Na +, K + was also found to positively enhance the NADH oxidase activity of strain M93. This tendency has not been recognized in other marine Vibrios. Furthermore, the Na +-dependent NADH oxidase of strain M93 required less Na + (0.1 M) for its maximum activity than those of other Vibrios such as Vibrio alginolyticus and ‘ Vibrio angustum’ S14, which were in the range of 0.4 M NaCl, similar as seawater. Destruction of H + motive force by a proton conductor carbonylcyanide m-chlorophenylhydrazone (CCCP) revealed high dependency of V. anguillarum on the primary H + pump. Even at pH 8.5, V. anguillarum strains other than serotype O-4 could not grow well with the addition of CCCP. In contrast, marine-type Vibrios such as V. alginolyticus and V. angustum S14 can grow well at pH 8.5 even with the addition of CCCP. The lower requirement for Na + in V. anguillarum probably reflects the salinity of their original habitats.

Salinization of a fresh palaeo-ground water resource by enhanced recharge.

Deterioration of fresh ground water resources caused by salinization is a growing issue in many arid and semi-arid parts of the world. We discuss here the incipient salinization of a 10(4) km2 area of fresh ground water (<3,000 mg/L) in the semiarid Murray Basin of Australia caused by widespread changes in land use. Ground water 14C concentrations and unsaturated zone Cl soil water inventories indicate that the low salinity ground water originated mainly from palaeo-recharge during wet climatic periods more than 20,000 years ago. However, much of the soil water in the 20 to 60 m thick unsaturated zone throughout the area is generally saline (>15,000 mg/L) because of relatively high evapotranspiration during the predominantly semiarid climate of the last 20,000 years. Widespread clearing of native vegetation over the last 100 years and replacement with crops and pastures leads to enhancement of recharge rates that progressively displace the saline soil-water from the unsaturated zone into the ground water. To quantify the impact of this new hydrologic regime, a one-dimensional model that simulates projected ground water salinities as a function of depth to ground water, recharge rates, and soil water salt inventory was developed. Results from the model suggest that, in some areas, the ground water salinity within the top 10 m of the water table is likely to increase by a factor of 2 to 6 during the next 100 years. Ground water quality will therefore potentially degrade beyond the point of usefulness well before extraction of the ground water exhausts the resource.

The genus Microvelia Westwood in Australia (Hemiptera : Heteroptera : Veliidae)

Water striders and their allies (Hemiptera, Gerromorpha) are familiar inhabitants of water surfaces throughout the world. One of the most species-rich groups is the subfamily Microveliinae (Veliidae) and, in particular, the genus Microvelia Westwood, 1834. This genus comprises small or very small bugs inhabiting the nearshore areas of stagnant or slow-flowing fresh water. Accumulation of material during the past 30 years has shown that the Australian fauna of Microvelia is much richer and more diverse than previously recognised. In the present paper we discuss the subgeneric classification of the genus Microvelia based on the results of a phylogenetic analysis using maximum parsimony, describe three new subgenera and redescribe all previously known Australian species of the genus. The new taxa are: Microvelia (Austromicrovelia), subgen. nov. (type species: Microvelia mjobergi Hale, 1925) with the species Microvelia (Austromicrovelia) spurgeon, M. hypipamee, M. margaretae, M.�monteithi, M. tuberculata, M. myorensis, M. woodwardi, M. carnarvon, M. annemarieae, M. mossman, spp. nov. (all from Queensland), M. eborensis and M. milleri, spp. nov. (New South Wales), M. queenslandiae, M.�ventrospinosa, spp. nov. (New South Wales, Queensland), M. angelesi, M. alisonae, M. odontogaster, spp. nov. (Northern Territory), M. apunctata, sp. nov. (Northern Territory, Queensland), M. pennicilla, sp. nov. (Northern Territory, Western Australia), M. herberti, M. malipatili, M. torresiana, and M. australiensis, spp. nov. (Northern Territory, Queensland, Western Australia), Microvelia (Barbivelia), subgen. nov. (type species: Microvelia barbifer, sp. nov.) with the species Microvelia (Barbivelia) barbifer, sp. nov. (Queensland) and M. falcifer, sp. nov. (Northern Territory); Microvelia (Pacificovelia), subgen. nov. (type species: Microvelia oceanica Distant, 1914) with the species M. tasmaniensis, sp. nov. (Tasmania), M. lilliput, and M. kakadu, spp. nov. (Northern Territory, Queensland, Western Australia). We further recognise the subgenus Microvelia (Picaultia), stat. nov. (type species: Picaultia pronotalis Distant, 1913), and describe the following new species: Microvelia (Picaultia) justi and M. paramega, spp. nov. (Northern Territory, Queensland, Western Australia), and M. cassisi, sp. nov. (New South Wales). Finally, Microvelia fluvialis weiri Malipatil, 1980, is synonymised with Microvelia fluvialis Malipatil, 1980. Keys to adults of all species are provided and their distributions mapped.

CONTAMINATION PAR ANGUILLICOLA CRASSUS DE CINQ POPULATIONS D’ANGUILLES (ANGUILLA ANGUILLA) DU LITTORAL DE BRETAGNE SUD (FRANCE)

Les anguilles prélevées dans cinq zones de salinité variable du littoral de Bretagne sud, ont été examinées pour leur infestation présente et passée par le parasite Anguillicola crassus (Nematoda, dracunculoidea). Les anguilles vivant dans des milieux peu salés au contact de la zone dulçaquicole sont très contaminées avec des prévalences supérieures à 90%, dont 61% concernent des prévalences présentes. Par contre, celles vivant dans des conditions estuariennes (Golfe du Morbihan) sont relativement épargnées avec des prévalences de l’ordre de 15%, dont en moyenne moins de la moitié concernent des prévalences présentes. La salinité des baies et des estuaires semble donc pouvoir préserver de la contamination les populations d’anguilles côtières dont la gestion devient un enjeu prioritaire pour le stock d’anguilles.

Growth performance and use of natural food by Oreochromis niloticus (L.) in polyculture systems with Barbodes gonionotus (Bleeker) and Cyprinus carpio (L.) in intensively cultivated rice fields

In the freshwater area of Vietnam's Mekong Delta, Oreochromis niloticus (L.), Barbodes gonionotus (Bleeker) and Cyprinus carpio (L.) are often reared together in rice fields. In this study, we report the results of eight such polyculture experiments, examining variables affecting the specific growth rate and the average daily food energy consumption of individual O. niloticus. The standing biomass of O. niloticus and the wild fish biomass had a negative impact on the specific growth rate, whereas added pig manure, extra feed and inorganic fertilizer had a positive effect. The standing biomass of O. niloticus and C. carpio, and the wild fish biomass had a negative impact on the consumption of natural feed. We inferred that O. niloticus mainly lacks food in rice fields. This results in intraspecific competition. As in rice fields, C. carpio has basically the same feeding niche as O. niloticus; we found interspecific competition between the two species. O. niloticus consumed relatively more food in the vegetative phase of the rice crop, probably because of a higher abundance of phytoplankton. To get higher growth of O. niloticus, we recommend that farmers increase nutrient inputs and stock O. niloticus according to the size of the trench adjoining the rice field and not according to the size of trench plus field as is generally done.

Distribution of free-living amoebae in James River, Virginia, USA.

A comprehensive survey to document the presence of free-living amoebae was conducted along 58 km of James River, near Richmond, Virginia, USA. Sites included tidal and non-tidal freshwater areas, near 40 combined sewer outflows, three municipal wastewater treatment plant release sites, and thermal discharge from a coal-fired power plant. Amoebae were present on all collection dates, spring through autumn, and at all sites ( n=330). Five genera, Naegleria, Vannella, Acanthamoeba, Vahlkampfia, and Hartmannella were present in both the water column and sediment. The most common isolates from the water column were Naegleria and Vannella. Water conditions conducive to the presence of large quantities of fecal coliform bacteria were correlated with the prevalence of free-living amoebae. Some of the amoebae in this complex ecosystem can act as opportunistic pathogens, may play a role in diseases of aquatic organisms in this heavily urbanized river, and may present a risk to human health.

Detection of Neorickettsia ( Ehrlichia) risticii in tissues of mice experimentally infected with cercariae of trematodes by in situ hybridization

Neorickettsia (Ehrlichia) risticii was demonstrated to occur in cercariae developing in Juga yrekaensis snails by experimental transmission, genetic detection and histopathology. Cercariae were isolated from the digestive glands of snails collected in a fresh stream water area of Siskiyou County, CA, and inoculated into CF1 mice. Mice developed clinical signs, splenomegaly and histopathologic abnormalities. The agent was maintained by serial passages of whole blood in CF1 mice. A 527-bp product of the 16S rRNA gene of N. risticii was serially detected by nested PCR in blood, feces, salivary gland, suprarenal gland, spleen, intestine and bone marrow of inoculated mice. N. risticii DNA was detected by in situ hybridization with DIG-labeled probe in PCR-positive salivary gland, intestine and spleen tissue sections of experimental mice on day 30 after inoculation. Infection in mice was established when cercariae were inoculated by either IP or SC routes but not established following intraoral route. N. risticii was detected by PCR in spleen, intestine and bone marrow even after 73 days post-inoculation whereas blood from the same animals became negative at 58 days. N. risticii was observed by in situ hybridization in salivary gland, spleen and intestine of mice infected by IP or SC inoculation. This ISH protocol should aid investigations on the host range of the Neorickettsiosis and pathogenesis of neorickettiosis in vector, animal or human.

Protist functional groups in a sublittoral estuarine epibenthic area

Protist communities were studied monthly at Santona beach (Cantabrian Sea, Spain) throughout one year. Twelve abiotic parameters were analyzed. The following functional groups (defined according to the preferential source of food) were considered: photoautotrophs (P), saprotrophs (S), bacterivores (B), algivores (A), non-selectives (N), and predators or raptors (R). A total of 269 species was found. The percentage of species in each functional group was: 11.66% A, 33.66% B, 26.45% N, 28.02% P, and 0.21% R. No species belonging to functional group S were found. Functional groups B and N had the highest percentage of biomass (up to 100% in certain months). The percentage of biomass for each functional group was calculated. There was a remarkable negative correlation between groups B and N at the four sampling sites. The biomass percentage of group A was important at several sampling points in March, June, and July, coinciding with an increase in their source of food. The percentage of group P rose in April and May, the months the period of irradiance was longer. The canonical population analysis showed that there were no significant differences with respect to the composition in terms of functional groups at the four sampling sites. These data were compared with those found in the literature on both marine and freshwater areas, by means of a hierarchical conglomerate analysis. The statistical analysis showed that there are generally noticeable differences between these two types of media. It is suggested that each area may have a characteristic species composition respect to functional groups, which is influenced by the environmental parameters.

Landscape characteristics, land use, and coho salmon (Oncorhynchus kisutch) abundance, Snohomish River, Wash., U.S.A.

We used temporally consistent patterns in the spatial distribution of returning adult coho salmon (Oncorhynchus kisutch) to explore relationships between salmon abundance, landscape characteristics, and land use patterns in the Snohomish River watershed, Wash. The proportion of total adult coho salmon abundance supported by a specific stream reach was consistent among years, even though interannual adult coho salmon abundance varied substantially. Wetland occurrence, local geology, stream gradient, and land use were significantly correlated with adult coho salmon abundance. Median adult coho salmon densities in forest-dominated areas were 1.5–3.5 times the densities in rural, urban, and agricultural areas. Relationships between these habitat characteristics and adult coho salmon abundance were consistent over time. Spatially explicit statistical models that included these habitat variables explained almost half of the variation in the annual distribution of adult coho salmon. Our analysis indicates that such models can be used to identify and prioritize freshwater areas for protection and restoration.

Desorption of phosphate from sugarcane soils into simulated natural waters

A laboratory-based study of the behaviour of phosphorus (P) was carried out on the soils of the lower Herbert River catchment, Queensland, Australia. The aim was to explore the potential for P sorption or desorption by Herbert soils in associated river and estuary waters, so that the extent of problems associated with sugarcane production and soil-derived inputs to streamwater could be defined. Anion exchange resin was used as a sink for P. The equilibrium phosphate concentration (EPC) measured in simulated soil pore water (0.01M CaCl2), and the EPC in the simulated river and estuary waters were strongly correlated. Based on this, and the close relationship between P sorption and selected soil properties, it was possible to estimate P desorption using commonly measured properties. Much less desorption of P took place in simulated estuary waters than in simulated river water of much lower ionic strength. This suggests that environmental degradation arising from the downstream export of soil-borne P from Herbert cane lands is likely to be concentrated in freshwater areas. Sorption properties of P in soils of the lower Herbert appear to be closely associated with aluminium-rich minerals, rather than with iron (hydr)oxides.