首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到10条相似文献,搜索用时 125 毫秒
1.
Abstract – Resource partitioning between Atlantic salmon parr, brown trout and Arctic charr was studied throughout the ice-free season in a north Norwegian lake. Juvenile salmon and trout (≤160 mm) utilized the littoral zone and juvenile charr the profundal, while adult trout and charr (>160 mm) were found in both. Juvenile salmon and trout had a similar diet, although trichopteran larvae were more important for the trout and chironomid pupae and three-spined sticklebacks for the salmon parr. Small salmon and trout parr (≤120 mm) had a higher diet overlap than larger parr (121–160 mm). The feeding habits of adult trout were similar to that of juvenile trout, but the former took larger prey items. At the population level, both salmon and trout were generalistic feeders with a broad diet, but at the individual level, both species had specialized on a single or a few prey categories. Juvenile charr were segregated from salmon and trout in both habitat and food utilization; they had a narrow diet consisting of chironomids and zooplankton, possibly reflecting their confinement to the profundal habitat which have a low diversity of potential prey. Larger charr also took zoobenthos and sticklebacks in the littoral zone. Note  相似文献   

2.
Atlantic salmon, Salmo salar L., and brown trout, Salmo trutta L., fry were point and scatter stocked in the early part of June at densities of 63–263 fry 100 m−2 per species in the River Viantienjoki, a small river in northern Finland, and their population densities were assessed in late summer. Both species were always stocked together in similar quantities. Point stocking was used in the first 2 years and scatter stocking in the following 2 years. In point stocking, there was no correlation between the distance from the stocking sites (maximum = 250 m) and parr density in census sites ( r = −0.013 and 0.019 for brown trout and Atlantic salmon, respectively). The stocking density of fry did not influence parr density in August by either method or by species. Stocking density explained only from 11% to 23% of the parr survival depending on the species or stocking method. The mean densities of Atlantic salmon and brown trout parr did not differ significantly from each other at any fishing site ( P > 0.05). Both point and scatter stocking appear to be suitable methods for use in small rivers. The parr densities depend more on the other factors (e.g. habitat quality) than the stocking method, and the choice between methods could be based on the time and labour available.  相似文献   

3.
Abstract –  Lipid density appears to influence life-history decisions in salmonid fishes. This study shows that parr and smolts of anadromous Atlantic salmon from a south Norwegian river have on average between 30 and 40% higher energy level than corresponding brown trout in spring and summer, which may explain differences in life-history traits between the two species. The higher energy density of young salmon was chiefly due to a 1.8 times higher lipid density in parr and 2.4 times higher lipid density in smolts. The difference was smaller among immature parr in the autumn, with only 1.4 times higher lipid density in salmon than trout. The reason for the decreased difference was probably that the more energy rich salmon parr had attained maturity at the time. Among mature male parr, the somatic energy density was approximately 10% higher in trout than salmon. However, the gonadal energy content was more than twice as high in salmon than in trout. The higher somatic energy allocation in parr of Atlantic salmon probably influences protein growth of the two species in fresh water, and increases the ability of salmon relative to trout to undertake long distance feeding migrations and make large investments in reproduction.  相似文献   

4.
Abstract –  Downstream movement of a wild population of brown trout was examined in a small Danish stream in relation to morphological and physiological smolt status from March to May. Downstream movement was monitored in a Wolf-type trap covering all possible passage routes in the stream. Trout caught in the trap were classified as parr, pre-smolt or smolt based on morphological criteria and compared with trout randomly caught by electrofishing upstream of the trap. Representative gill samples from trap-caught and electrofished trout were analysed for gill Na+, K+-ATPase activity and used as a measure of physiological smolt status. Only a few parr occurred in the trap. Few pre-smolts occurred in the trap evenly in March and early April. In late April, pre-smolt movement peaked. By comparison, the main downstream movement of smolts occurred in distinct peaks through late March and April. The majority of fish caught in the trap were judged as pre-smolts or smolts based on morphological criteria's and they were characterised by relatively high gill Na+, K+-ATPase activity compared with trout judged as parr. Trout caught by electrofishing upstream the trap, were classified as parr, pre-smolts and smolts early in the season (March). During and after the main smolt-run in April the distribution of the remaining trout in the brook became skewed in favour of pre-smolt and parr. The study suggests that smolting trout initiate downstream movement once having reached a certain physiological smolt condition (judged by increased gill Na+, K+-ATPase activity).  相似文献   

5.
Abstract The influence of environmental factors on the density and biomass of stocked brown trout, Salmo trutta L., parr was studied in brooks subjected to intensive forestry in the Isojoki river basin, western Finland. Multivariate regression analysis showed that 69% of the variation in the population density of parr was determined by five variables: (1) mean water depth; (2) the abundance of pools; (3) stony bottom substrates with stones sized between 2 and 10cm in diameter; (4) undercut banks; and (5) the percentage of shading by trees. Correspondingly, 57% of the variation in the biomass of parr was determined by three variables: (1) mean water depth; (2) the abundance of pools; and (3) benthic vegetation. Dredging of the brooks and forest ditching had the most harmful consequences for the nursery habitats of brown trout parr. Measures for the rehabilitation of brown trout production in these brooks are discussed.  相似文献   

6.
Brown trout Salmo trutta L. parr were sampled from 21 Estonian and three Finnish streams to investigate whether national sea trout parr surveys sample the progeny of anadromous or resident maternal parents. Otolith Sr:Ca core values were used and validated as a tool for distinguishing between the progeny of the two forms. In Estonia (= 283), 92% of the parr were the progeny of anadromous maternal parents, and 8% were the progeny of resident maternal parents, whereas in Finland (= 24), the respective proportions were 79% and 21%. Variation in the maximum otolith Sr:Ca core values among progeny of anadromous maternal parents indicated that some adult females may enter fresh waters several months before spawning. It was concluded that easily accessible locations situated up to 30 km from the sea largely contain progeny of sea trout, whereas sites with poor connectivity with the sea can be dominated by progeny of resident trout. This study demonstrated that the method applied provided an effective means to distinguish between the progeny of sea trout and resident brown trout.  相似文献   

7.
Abstract – In past dietary studies kokanee Oncorhynchus nerka were prominent in the diet of Pend Oreille Lake's large piscivores: native bull trout Salvelinus confluentus, cutthroat trout O. clarki and northern pikeminnow Ptychocheilus oregonensis, and introduced lake trout S. namaycush and Kamloops rainbow trout O. mykiss gairdneri. However, kokanee have declined to 10–20% of their former abundance. We therefore initiated this study to understand current predation demands on kokanee and diet overlap among piscivores, using gut content samples and analysis of stable nitrogen (δ15N) and carbon (δ13C) isotopes from the lake's fish and invertebrate community. In gut content samples, kokanee were the main prey item of large [i.e., ≥400 mm total length (TL)] bull and lake trout; a conclusion that was affirmed by stable isotope analysis. Rainbow trout >500 mm TL consumed mostly kokanee, thus there was a high degree of diet overlap among large bull, lake and rainbow trout. Small (i.e., <400 mm TL) rainbow and cutthroat trout diets overlapped, and were composed mostly of littoral benthic invertebrates. However, gut content and stable isotope analysis did not accord for 400–500 mm TL rainbow trout, small lake trout, and large cutthroat trout. In these instances, a linear mixing model using stable isotope results predicted kokanee consumption for each species, but no kokanee were identified in rainbow or lake trout gut content. Gut content and stable isotope analysis of native northern pikeminnow indicated a diet of mostly littoral benthic invertebrates at smaller (100–150 mm TL) lengths, with kokanee becoming more prominent in the diet of individuals >300 mm TL. Percent of kokanee in the diet of northern pikeminnow has declined from a prior study; otherwise piscivore diets have apparently remained unchanged. In this study, judgments as to the feeding of some piscvores, based on gut content alone, would be tenuous because of small sample sizes, but stable isotope analysis provided an efficient means for confirming diets.  相似文献   

8.
Abstract – The size of 2-month old trout Salmo trutta parr differed between sites and between years along the River Esva catchment (Asturias, northwestern Spain). Such variation was in a direction opposite to the variation observed in parental size. Parr were smaller in sites where parents grew faster, whereas larger parr occurred in sites where parents grew less. Parr size of six cohorts (1990–1996, except 1995) at 14 sites along the River Esva was inversely related to the growth rate and length of parents and positively related to canopy, egg size, and water temperature. The latter acted similarly on all parr independently of egg size and the site where the egg originated. Covariation patterns among parr size, parental traits, and canopy suggest that a canopy-regulated, growth-determined trade-off between egg size and number, previously described for the Esva trout, also extends to alevin size. In forested, shaded sites, adult trout grew less and spawned fewer larger eggs that resulted in larger alevins, whereas in fully insolated, production-rich sites, trout grew faster and spawned higher numbers of smaller eggs that produced smaller parr. I hypothesize that the phenotypic plasticity illustrated by the environmentally induced trade-off between egg size and number further extended to alevin size may be evolutionarily advantageous because it relates the size of trout alevins to food availability, as predicted by the growth previously experienced by parents. NOTE  相似文献   

9.
The effect of Gyrodactylus salaris on the epidermal structure of hatchery-reared brook trout parr and Norwegian Atlantic salmon parr was evaluated. Both species were initially susceptible to this parasite, but whereas populations on salmon increased until the host died, brook trout responded to, and eventually eliminated, their infections. Salmon skin samples taken 14 days p.i. showed a reduced mucous cell concentration (less than 1500 cells mm–2 on the head compared with 2000 cells mm–2 in controls; the same trend was also seen in other sites) and the epidermis was thinner (48 μm compared with 60 μm on pectoral fins; similar trend seen in other sites) than in uninfected controls kept under identical conditions. Brook trout skin samples were taken 50 days p.i., when the hosts had responded to, and almost eliminated, their infections. No change was then observed in mucous cell density, while the number of epidermal cell layers and the epidermal thickness of brook trout had increased slightly following infection. These results are related to the nature of the host response, and the thinning of the epidermis and loss of mucous cells may in some way be related to the inability of Norwegian salmon parr to respond to the parasite.  相似文献   

10.
Abstract Proliferative kidney disease (PKD) has been described in cultivated rainbow trout but major outbreaks have not been recognized in other fish species. This paper describes light and electron microscope studies and presents epidemiological data of a disease condition in first summer Salmo salar parr and S. trutta , which is associated with an organism apparently identical to the aetiological agent of PKD. The pathology was found to be similar to that described for PKD in rainbow trout. The epidemiology in the brown trout suggests that exposure after May does not result in infection. The data from the outbreaks in two salmon hatcheries appear complex and suggest different susceptibilities to PKD among salmon originating from different sources.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号