共查询到20条相似文献，搜索用时 46 毫秒
1.
2.
《Limnologica》2015
Unionoid mussels are obligate parasites on one or more fish species. The objective was to compare growth and survival of encysted mussel larvae of the freshwater pearl mussel (Margaritifera margaritifera) on young-of-the-year (YOY) versus one-year old brown trout (Salmo trutta). YOY and one-year old trout from the Brattefors and Lärje Rivers, Sweden, were infested with mussel larvae from their home river. The mass-normalized encystment abundance was higher on YOY trout than on one-year old trout. The proportional decrease in mass-normalized encystment abundance was larger on YOY brown trout from the Brattefors River than on YOY brown trout from the Lärje River. Encystment per individual fish was higher on YOY trout than on one-year old trout from the Brattefors River, whereas this relationship was reversed for trout from the Lärje River. Larval growth was higher on YOY trout than on one-year old trout. There was a larger difference in larval growth between YOY trout and one-year old trout from the Brattefors River than on the brown trout from the Lärje River. The ability to use both YOY and older fish, such as in the Lärje River, may increase the reproduction potential of mussel populations, compared to a reduced ability to use more than one year class, such as in the Brattefors River. This may also affect the dispersal of mussels, as older brown trout often move and migrate to a higher degree within and between rivers. The dispersal potential of mussels may therefore be relatively high in the Lärje River, but low in the Brattefors River. In rivers where the mussels have to rely on YOY brown trout, it could be worth facilitating passage through migration obstacles for YOY brown trout. Infested YOY brown trout could be artificially re-distributed within rivers, to places with former mussel distributions. It could also be worth testing the suitability of brown trout of different age classes when starting breeding programs. 相似文献
3.
4.
5.
《Limnologica》2017
During the past two-three decades the water chemistry in southern Norway has recovered considerably from acidification. The biological response, however, has been more variable. Thus, it has become increasingly apparent that decades of acidification may have masked other restrictors to fish populations in this area. The current study compiles data on young brown trout (Salmo trutta) density and water chemistry from 16 sites in River Sira in southwestern Norway during 2003–2014. The water chemistry during late snowmelt period was highly dilute, having a median conductivity and Ca of 10.5 μS/cm and 0.42 mg/l, respectively (n = 208). The corresponding minimum values were 5.0 μS/cm and 0.15 mg/l. With a pH median value of 5.89, the water was only slightly acidic. No effect of pH on the density of young brown trout was found, suggesting that acidification is no longer a limiting factor. However, both conductivity in year n-1 and Ca in year n correlated significantly with the density of 1+ brown trout. Al in year n, and surprisingly Ca in year n-1, correlated negatively on their densities. We conclude that very dilute water chemistry during late snowmelt is a limiting factor for the recruitment of brown trout in the study river. This effect has probably existed in the past as well, but has been less apparent due to decades of severe acidification. 相似文献
6.
《Limnologica》2015
Many of the unionoid mussel species are threatened, and to be able to develop strategies for effective conservation, one of the needs is to distinguish host fish species from non-host fish species using reliable methods. Margaritifera margaritifera lives as a parasite on brown trout (Salmo trutta) and/or Atlantic salmon (Salmo salar). The aim was to compare the reliability of two methods measuring the host specificity of M. margaritifera in two rivers that flow out into Skagerrak in the Atlantic Ocean. A second aim was to compare the time- and cost-efficiency of the two methods. The methods were (1) natural encystment abundances on fish in their native streams using electrofishing, and (2) encystment abundances from controlled artificial infestation in aquaria, on fish that were sacrificed. In both rivers, young-of-the-year (YOY), but not older brown trout, were naturally infested with relatively low loads of glochidia larvae, while the Atlantic salmon was not infested at all. When using artificial infestation, both YOY and older brown had encysted glochidia larvae on their gills, while glochidia larvae were not able to develop in Atlantic salmon at all. Here, the encystment was higher on the brown trout from the Lärje River, and older brown trout from the Lärje River did not seem to have as strong immunity response compared to older brown trout from the Brattefors River. In summary, brown trout is the only host fish for M. margaritifera in these rivers. Both methods can be used to discriminate between host fish species, but the method measuring natural encystment seems most time- and cost-efficient. In addition, natural encystment can be measured using a non-destructive photo-method, and is therefore suggested to be used when discriminating between host fish species for M. margaritifera. 相似文献
7.
8.
Franz Lahnsteiner Reinhard Haunschmid Nabil Mansour 《Aquatic Sciences - Research Across Boundaries》2009,71(4):463-472
For several years, severe brown trout (Salmo trutta) mortality has been observed in different prealpine river systems of Austria, Southern Germany, and Switzerland during late summer and early autumn. Often, the skin of the effected fish shows a medium to intense black pigmentation, and therefore this phenomenon is called “Schwarze Bachforelle Phänomen” or “proliferative darkening syndrom”. The present study was conducted to gain insight about its presence. From middle of May to end of August, brown trout and rainbow trout were kept in experimental tanks supplied with water from an effected river system. In brown trout, samples for blood diagnostics and histological investigations were taken after 0, 47, 62, and 77 days, and in rainbow trout after 0 and 107 days. Brown trout from a wild population were investigated for comparative purposes. Brown trout showed no abnormalities till the end of June. All fish sampled in the second half of July suffered from severe immune deficiency as the numbers of peripheral blood granulocytes and lymphocytes, plasma lysozyme activity, and plasma immunoglobulin levels significantly decreased. During August, the number of erythrocytes decreased and the osmotic fragility of the erythrocytes increased. Senescent erythrocytes became more frequent and the hematopoietic tissue of spleen and kidney enlarged. Also, the cellular composition of the spleen changed as the number of hemoblasts and normal erythroblasts decreased while the number of atypical erythroblasts increased. In the pronephros and hematopoietic tissue of the mesonephros, aggregation of macrophages and tissue disintegration was frequently observed. This was similar for brown trout from the field experiment and from the wild population. High mortality occurred in the end of July and during August. Death of the fishes might have been caused by secondary infections with microorganisms. Almost similar changes were observed in rainbow trout, however, the mortality was lower. 相似文献
9.
《Limnologica》2016
Dairying is an intensive form of agriculture influencing stream ecosystems worldwide via increased levels of nutrients, deposited fine sediment and other contaminants. However, it is not fully understood how dairy farming affects food supply for stream fish. We investigated relationships between dairy farming prevalence in the catchments of nine tributaries of a New Zealand river (0% to 79% of the catchment area) and fish and invertebrate communities. Streams were sampled four times at monthly intervals for brown trout density, fitness/growth-related trout response variables, native fish density, invertebrate community metrics as well as physical and chemical water quality variables. Densities of both brown trout and native fish declined as dairying increased, with no trout found in streams where dairy farms covered more than 50% of the catchment area. Increasing dairy farming prevalence was also associated with higher in-stream levels of dissolved nutrients and deposited fine sediment. These findings suggest that increasing the extent of dairy farming in New Zealand based on practices at the time of sampling results in less abundant and diverse fish communities. 相似文献
10.
11.
13.
Nesameletidae is a Southern Hemisphere ephemeropteran family with large-bodied nymphs that are swimming grazers, traits that make aquatic invertebrates vulnerable to visual predators. Metamonius anceps is the sole representative of this family in South America and its present known distribution along the Southern Andes is mostly restricted to headwater streams, usually with clear and well-oxygenated waters.We analyzed their spatial distribution in relation to the presence of the exotic predator rainbow trout (Oncorhynchus mykiss), which is the only fish species in many small Andean Patagonia streams. We measured mayfly abundance in the benthos and drift in reaches with and without fish (the latter being reaches upstream of waterfalls that prevent trout access) in three catchments of Nahuel Huapi Lake basin at the Nahuel Huapi National Park, Argentina. We compared nymphal abundance and body size at the habitat scale and at the reach scale, and nymphal presence and body size in trout diet.A multivariate analysis of physical stream features showed that habitat/reaches with and without fish had similar abiotic characteristics. In no fish sites, nymph density ranged between 44 and 180 m−2 while in fish sites they were 0–3 m−2. In one stream nymphs drifted mainly during the day and ∼400 indiv. day−1 were estimated to enter the site with fish. However no nymphs were collected drifting 200 m below the waterfall (the reach with fish). Observations on the diet of rainbow trout also supported the ongoing strong interaction between this mayfly and the trout. M. anceps is a highly vulnerable prey as no permanent populations were found in study reaches with the exotic predator established. Our study emphasizes the potential of natural physical barriers to stop invasive fish having access to headwaters allowing them to harbour natural populations of the most trout-susceptible species supporting pristine ecosystem conditions. 相似文献
14.
Rivers and streams are unstable environments in which estimation of energetic costs and benefits of habitat utilization are the daunting exercise. Empirical models of food consumption may be used to estimate energetic benefits based on abiotic and biotic conditions in patches of habitat. We performed thirty daily surveys of fish stomach contents to estimate the consumption rates for juvenile Atlantic salmon (Salmo salar) in a river. The data were used to assess whether variations of daily consumption rates existed within the river, and to develop empirical models that could predict fish consumption rates using abiotic and biotic conditions as independent variables. Daily consumption rates based on stomach content surveys in the field (range: 0.15–1.49 g dry/(100 g wet day)) varied significantly depending on habitat patch (500–1000 m2), summer period, and sampling year. Variables such as water temperature, numerical density of salmon, water depth and moon phase explained 83–93% of the variations in daily food consumption rates. Daily consumption rates tended to increase with water temperature and depth, and were also higher near a full moon. However, they tended to decrease with the numerical density of salmon. Our work suggests that empirical models based on independent variables that are relatively simple to estimate in the field may be developed to predict fish consumption rates in different habitat patches in a river. 相似文献
15.
16.
17.
J.-M. Ribi J.-L. Boillat A. Peter A. J. Schleiss 《Aquatic Sciences - Research Across Boundaries》2014,76(4):527-541
Peak power production in hydroelectric storage power plants results in frequent and intense flow variations in the rivers downstream of the plants. Fish populations can be negatively impacted when subjected to these so-called hydropeaking phenomena. In researching mitigation solutions, shelters in the riverbanks of channelized rivers have been identified as a means of protecting fish from excessive flow velocities. These shelters were studied systematically using juvenile brown trout (Salmo trutta fario) in an experimental configuration in which a straight channel was equipped with a lateral embayment. The purpose of the experiments was to generate hydrodynamic hydropeaking conditions in the channel that are undesirable for juvenile trout, thereby causing them to enter the shelter. The flow velocity distribution in the intersection plane between the main channel and the lateral shelter was found to be a significant parameter for attracting fish to the shelter. The utilization rate of trout in the shelter was used as a performance indicator. Using a basic rectangular shelter configuration without forced water exchange between the shelter and the channel, the utilization rate was only 35 %. This rate was more than doubled by introducing a deviation groyne to force water exchange between the channel and the shelter. The position and orientation angle of this groyne were systematically varied to maximize the utilization rate. Maximum utilization rates approaching 90 % were obtained for an optimum configuration in which an island-type groyne was placed in the shelter. The results of the systematic channel tests showed the potential of the shelter to attract fish. Such a shelter could be used in channelized rivers both for morphological revitalization and to improve fish habitats. As a next step in this research, prototype shelters will be built on a natural river and monitored for 2–3 years under a hydropeaking flow regime. 相似文献
18.
In order to understand the structure of fish assemblages in the modified Lima basin (Northern Portugal), two distinct datasets concerning the presence and abundance of fish species were subjected to multivariate analysis. On the River Lima two types of flow modification are present within kilometres of one another: (a) a reduced and constant flow due to hypolimnetic release; and (b) an intense and irregular flow. A comparison of their influence on fish assemblages revealed a gradient of assemblage types from tributaries to main river sites. The latter were characterised by a strong dominance of cyprinids, particularly Iberian barbel (Barbus bocagei). The former harboured two kinds of fish assemblages: those closer to the river mouth were dominated by the cyprinids Iberian chub (Squalius carolitertii) and Iberian nase (Chondrostoma polylepis), which were also frequently present in the main river; while in those further upstream the predominant species was the brown trout (Salmo trutta). Although explanatory variables such as distance from source, altitude, substrate coarseness and width were the primary correlates of fish assemblage composition, dam construction and flow regulation also had a significant effect upon assemblage structure, particularly by: i) reducing the importance of migratory species; ii) constraining the presence of trout in the regulated segments; and iii) simplifying the community, especially in the case of the constant and reduced flow regime. 相似文献
19.
Ximena Aguilera Steven Declerck Luc De Meester Mabel Maldonado Frans Ollevier 《Limnologica》2006,36(4):258-268
Tropical high Andes lakes are aquatic ecosystems with peculiar limnological characteristics that are related to their geographical location and high altitude, yet they remained understudied. We present the results of a standardized survey of morphometric, physico-chemical and biotic variables in 32 high altitude lakes of the Cordillera del Tunari (Eastern Andes of Bolivia). Based on the variables measured, we identified three lake types. One group of lakes differed from the other lakes by a relatively high pH and biological productivity (as evidenced from higher densities of phytoplankton, zooplankton, and fish). A second group of lakes consisted of relatively large and deep water bodies with neutral to slightly acid pH and with a relatively high occurrence of the large cladoceran Daphnia pulex. The third group contained relatively small, shallow, and acid lakes with no Daphnia. Rainbow trout occurred in more than half of the lakes and catch yields were very variable. Overall, the abundances of different organism groups tended to be positively associated (e.g. phytoplankton, copepods, rotifers, fish) indicating the existence of a major productivity gradient. We found no negative associations between trout catches and densities of any of the major zooplankton groups, suggesting moderate to low top-down effects of trout on the zooplankton communities. 相似文献