Otolith size differences during early life of dwarf and cannibal Arctic char (Salvelinus alpinus)

In Arctic and alpine lakes, Arctic char [Salvelinus alpinus (L.)] often form two distinct morphs: invertebrate feeders (‘dwarfs’) and piscivores (‘giant or cannibals’). Here, we test for early life history growth variation in dimorphic Arctic char as a proximate explanation for the observed life history variation between the two forms. Char were sampled in 11 alpine and Arctic Norwegian lakes. Dwarfs (defined as sexually mature char less than 15 cm long; N = 304) had a mean total length of 105 mm, whereas the typical cannibal (body length above 20 cm; N = 153) was 388 mm long. A positive correlation between egg size and otolith hatching ring were ascertained in a separate hatching experiment with brown trout (Salmo trutta) and it is assumed that this relationship also is valid for Arctic char, and otolith size was used as a proxy for length. Otolith hatching ring from Arctic char cannibals was larger (mean ± SD; 187 ± 24 μm) than those from dwarfs (mean ± SD; 164 ± 23 μm). There were only minor size differences between dwarfs and cannibals during the next three years, after which dwarfs usually matured. Two mutually nonexclusive, proximate explanations for the differentiation into separate morphs (dwarfs and cannibals) are therefore maternal effects and/or genetic based differentiation. The high catchability of large piscivorous char and low production in alpine and Arctic lake ecosystems may make these stocks particularly vulnerable to overexploitation.     

Latitudinal variation in growth and otolith‐inferred field metabolic rates of Canadian young‐of‐the‐year Arctic charr

Countergradient variation (CGV) is defined as genetic variation that counteracts the negative influences of the physical environment, minimising phenotypic variability along an environmental gradient. CGV is thought to have relevance in predicting the response of organisms to climate variability and change. To test the hypothesis that growth rate increased with latitude, consistent with CGV, young‐of‐the‐year (YOY) Arctic charr, Salvelinus alpinus, were examined along a ~27° latitudinal gradient in central and eastern Canada. Growth rates were estimated from fork lengths standardised by the thermal opportunity for growth based on experienced water temperatures derived using otolith oxygen stable isotopes. Results demonstrated patterns consistent with CGV, where northern populations demonstrated faster growth rates. A secondary aim was to test for similar geographical patterns in otolith‐inferred metabolic rates, which reflect the energetic costs of standard metabolic rate (SMR) and other processes such as feeding, locomotion, thermoregulation, reproduction and growth. Results demonstrated a significant, positive relationship between otolith‐inferred metabolic rate and latitude, which may reflect an increase in one, or a combination, of the above‐noted physiological processes. The similar latitudinal pattern in growth and otolith‐inferred metabolic rates suggests greater intake of food per unit of time by northern fish. The phenotypic variation in physiological traits observed here demonstrates the significant adaptability of Arctic charr to different thermal regimes with different growing season lengths. Determining the relative contributions of phenotypic plasticity and genetic variation to the observed latitudinal variation will be critical to predicting the responses of Arctic charr to climate change more accurately.     

4种鲑鳟鱼外周血细胞显微及超微结构比较

为研究鲑鳟鱼的血细胞形态学差异,采用光镜及电镜技术对白点鲑Salvelinus malma(体质量49.07 g±12.05 g)、红点鲑Salvelinus leucomaenis(体质量83.23 g±15.07 g)、虹鳟Oncorhynchus mykiss(体质量60.12 g±11.86 g)和金鳟Oncorhynchus mykiss(体质量42.04 g±10.26 g)4种鲑鳟鱼外周血细胞的组成、大小、显微及超微结构进行了研究。结果表明:4种鲑鳟鱼外周血细胞中可见红细胞、淋巴细胞、嗜中性粒细胞、血栓细胞及单核细胞,其中,红细胞占大多数,淋巴细胞数量仅次于红细胞,大淋巴细胞和嗜中性粒细胞密度在4种鲑鳟鱼中无显著性差异(P>0.05);4种鲑鳟鱼的成熟红细胞形态结构相似,血栓细胞形态多样,其他种类白细胞形态结构相似,白细胞均以血栓细胞和淋巴细胞为主体;白点鲑血栓细胞最多,成群结队排列,红细胞数量也较多,红细胞长径和短径均最大,单核细胞中富含细胞器,嗜中性粒细胞分叶较多;红点鲑红细胞和淋巴细胞数量也较多;虹鳟红细胞密度最小,淋巴细胞最多,嗜中性粒细胞长径和短径最大;金鳟红细胞和白细胞密度最大,淋巴细胞和血栓细胞长径和短径最大。研究表明,4种鲑鳟鱼外周血细胞的显微和超微结构特征与其他鱼类相似,但不同物种间血细胞数量和大小存在一定差异。     

患病北极红点鲑的病原分离与鉴定

对2004年5月四川省某养殖基地养殖的北极红点鲑患病鲑进行了病理学检查和病原分离,从病灶处分离到细菌和真菌。分离到的细菌经API生化鉴定为杀鲑气单胞菌杀鲑亚种(Aeromonas salmonicidasubsp.salmonicida)。用引物AP1和AP2对纯化后的细菌进行PCR扩增,结果扩增出长度为421 bp的DNA片段,对扩增片段进行克隆、测序,用NCBI-BLASTn在GenBank中搜寻相似序列,结果与杀鲑气单胞菌各株A层蛋白部分编码基因有99%以上的序列同源性。用引物EUS-F和EUS-R对分离到的真菌进行PCR扩增,结果扩增出长度为755 bp的DNA片段,对扩增片段进行克隆、测序,用NCBI-BLASTn在GenBank中搜寻相似序列,结果与水霉属各株的DNA片段(包括18S核糖体RNA基因部分序列、内转录间隔区1全序列、5.8S核糖体RNA基因全序列、内转录间隔区2全序列和28S核糖体RNA部分序列)有93%-100%的同源性;而与属于丝囊霉菌属的EUS各株相对应的DNA片段仅有60%的序列同源性。因此判定所分离的真菌为水霉。杀鲑气单胞菌是引起疖疮病和溃疡病等病的病原菌,而水霉广泛存在于水中,当鱼受伤后,水霉孢子容易从患病部位侵入鱼体,加重感染。因此判断该病主要是由杀鲑气单胞菌引起,而水霉则引起继发感染。     

Seasonal habitat use by brook trout,Salvelinus fontinalis (Mitchill), in a second-order stream

Abstract Seasonal habitat use by over-yearling and under-yearling brook trout, Salvelinus fontinalis (Mitchill), was examined in a second-order stream in north-central Pennsylvania, USA. The habitat occupied by brook trout and available habitat were determined in a 0.5-km stream reach during the spring, summer and autumn of 1989 and the spring and summer of 1990. Cover, depth, substrate and velocity were quantified from over 2000 observations of individual brook trout. Habitat used by under-yearling brook trout was more uniform between seasons and years than that used by over-yearling brook trout. Over-yearling brook trout occupied areas with more cover and greater depth than did under-yearling brook trout, suggesting ontogenetic shifts in these variables. Differences for velocity and substrate were not as great as those for cover and depth. The selection of areas with low water velocities governed trout habitat use in spring, whereas cover and depth were the most important habitat variables in summer and autumn. Principal component analysis showed that available habitat and trout habitat centroids diverged most in spring, indicating that habitat selection by brook trout may be greatest at this time.     

Conservation and management of the Arctic charr: a forward view

Abstract –  In this study, we synthesised the views of 34 participants in a workshop to consider the status and future conservation and management of the Arctic charr ( Salvelinus alpinus L.). These are expressed as a series of resolutions deriving from a conference on Arctic charr conservation held in Perth, Scotland in June 2004. Agreed resolutions from the conference were as follows. (i) The unique diversity of Arctic charr should be recognised for the contribution it makes to biodiversity of northern aquatic communities. (ii) The recognition by the public, nongovernmental organisations and national governments of the importance of Arctic charr in northern ecosystems is an important step to the management and protection that should be pursued. (iii) The taxonomic status of highly variable charr populations requires to be reviewed. (iv) There should be a separate system, complementary to the taxonomic one, which systematically catalogues the biological diversity of S. alpinus . (v) The Arctic charr provides a unique natural resource to study the process of evolution and this requires the highest level of protection from anthropogenic effects. (vi) The status of conservation policy for Arctic charr needs to be urgently reviewed to take account of its unique position in the fauna.     

The suitability of anadromous Arctic charr as host and vector of the monogenean Gyrodactylus salaris

Abstract –  In 2000, the Atlantic salmon ( Salmo salar L.) stock in the river Signaldalselva, North Norway was found to be infected with the monogenean Gyrodactylus salaris (Malmberg). This river system has a multispecies fish community of nine species in total. Low densities of Atlantic salmon parr were found during electrofishing in October (2003) with a prevalence of 94% and a mean abundance of 848 G. salaris. This watercourse also holds a riverine stock of anadromous Arctic charr ( Salvelinus alpinus ), which is not common in Norway. Among the parr of Arctic charr, 64% were infested with an abundance of 23 parasites per fish. The most heavily infected 0+ and 1+ juvenile Arctic charr had 469 and 534 parasites, respectively, indicating that the parasites are able to reproduce on Arctic charr in the wild. There was little variation in the rates of infestation of Arctic charr along the studied stretch of the river, even in areas with very low densities of Atlantic salmon parr. The parr of anadromous Arctic charr seem to be suitable as long-term hosts for G. salaris . Moreover, a few (22%) infested adult sea-running Arctic charr were captured after ascending the river in the autumn, which shows that large fish may also act as carriers of G. salaris . However, no parasites were recorded on potential anadromous Arctic charr before descending during early spring (April 2003 and April 2004). Thus, it is still not clear whether anadromous Arctic charr are able to disperse the parasite between watercourses. So far, it is uncertain whether G. salaris may increase the mortality rates of Arctic charr and thereby be a threat to these unusual occurring riverine anadromous Arctic charr stocks.     

Growth in Arctic charr and rainbow trout fed temporally concentrated or spaced daily meals

The effect on growth of distributing feed over a few hours compared tomore frequent meals was tested on 1+ Arctic charr (Salvelinus alpinus L.) and 1+ rainbow trout (Oncorhynchus mykiss Walbaum). Triplicate hatchery groups for each treatment were fed at a ration level of 1%/dayeither with few meals (8 times per day divided into morning and evening)or with frequent meals (32 meals equally distributed during the day). Wefound an opposite effect of meal frequency on growth in the two species.Low feeding intensity (8 meals per day) had a significantly positive effecton growth in rainbow trout but a significantly negative effect on growth inArctic charr when compared to feeding the fish frequent meals. Theopposite response to meal frequency is likely to be an effect of thedifferences in activity during feeding. Rainbow trout feed much moreaggressively than charr which can result in feeding being a more stressfulevent. In this experiment, the specific growth rate was lower and the feedconversion ratio higher for Arctic charr compared to rainbow trout.     

Growth of five landlocked Arctic charr stocks under hatchery conditions

Growth dynamics of five stocks of Arctic charr, were compared from the fry stage in June 1986 until December 1987. Each stock originated from a different lake in Sweden: Hornavan; Näckten; Torrön; Rensjön and Visjön. Hornavan charr reached the highest final mean weight (237 g), but they were not significantly heavier than Visjön charr (206 g). Growth of fish of the three remaining stocks was similar but less rapid. The superior growth performance of Hornavan charr was most pronounced during autumn. Coefficients of variation for individual size within stocks was between 30 and 54%, with Hornavan and Näckten charr displaying least variability. Charr from Lake Visjön had a significantly lower proportion of mature males (6%) than the other stocks (19–29%) at the end of the experiment. The results demonstrate that differences in growth potential exist between stocks of charr, and these differences may be related to differential seasonal rhythms in growth. Variations in early growth, size distributions and sexual maturation seemed to be subordinate factors affecting overall growth performance.     

Evidence for the recent extinction of two Arctic charr Salvelinus alpinus (L.) populations in the West of Ireland

1. This paper highlights the recent extinctions of two native Arctic charr populations in the West of Ireland, one population from the Lough Conn catchment, and a second from the Lough Corrib catchment, respectively. 2. The distribution of charr populations in the two catchments is reviewed. The current distribution information is drawn from recent fish stock surveys (Lough Corrib in 1996, and Lough Conn in 1997 and 1998). Previous records of charr in the literature and unpublished data are described to place the current distribution of charr within these catchments into a historical perspective. 3. The importance of the charr population in Lough Mask (Lough Corrib catchment) is emphasized, as it is one of the last extant examples of charr from a large Irish alkaline lake. 4. Impacts on charr populations in both catchments are discussed and conservation measures proposed. Copyright © 2001 John Wiley & Sons, Ltd.