美洲红点鲑溃烂病的病原菌研究

对从患病美洲红点鲑(Salvelinus fontinalis)体表患病部位和肾脏分离到菌株进行了鉴定及药物筛选。结果显示:人工感染试验证实为病原菌,该菌革兰氏染色阴性,菌体呈短杆状。综合该菌形态、生理生化分析结果初步鉴定两株菌均为杀鲑气单胞菌(American salvelinus)杀鲑亚种。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550 bp的DNA片段,对扩增片段进行测序,用NCBI BLAST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。进一步证明了鉴定结果。该菌对强力霉素、左氟沙星、氟罗沙星、庆大霉素等13种药物均敏感。     

美洲红点鲑血液生理生化指标和流变学性质的研究

首次测定美洲红点鲑血液生理、生化指标,同时测定5.75s-1,9.60s-1,11.50s-1,23s-1,46.0s-1,115.0s-1,230.0 s-1 7个切变率全血粘度和230s-1切变率测定血浆粘度。并统计分析生理和生化指标与全血粘度关系,结果表明影响全血粘度主要因子为血红蛋白(Hb)、红细胞压积(Hct)、血清总蛋白(Tp)、血清白蛋白(Ap)、血清胆固醇(Cho),而影响血浆粘度的主要因子是红细胞压积(HCT)。     

Preliminary investigations of the physiological adjustments associated with compensatory growth in juvenile brook charr (Salvelinus fontinalis)

Various physiological factors suspected to govern or be influenced by growth or feed intake of brook charr (80–120 g) were examined under long and short fasting periods during the year. A control (fed to satiation) was included. During winter, fasting (14 and 28 days) followed by refeeding led to a complete compensation. In summer, longer fasting (39 and 61 days) was applied to exacerbate the physiological response. Compensatory growth was observed in the restricted groups, and overall, adjustments/variations in growth and physiological indicators (feed conversion ratio, organosomatic index, enzymatic activities [CS, TRY, CHY]) were more pronounced. Degree of compensation reached was positively related to the deprivation duration. The summer experiment clearly suggests that compensatory growth takes place in two stages after a long starvation period (61 days): (1) restoration of the digestive system (PSI) followed by enzyme activities (trypsin and chymotrypsin) and (2) rebuilding of somatic tissues.     

The digestion and selective absorption of dietary fatty acids in Arctic charr, Salvelinus alpinus

To compare the rates of digestion and absorption of individual fatty acids, Arctic charr, Salvelinus alpinus (L.), were fed isoenergetic diets containing 40 g kg^?1 coconut oil, and various combinations of 10 g kg^?1 of polyunsaturated fatty acids (PUFA) (18:2n-6 or 18:3n-3) and monounsaturated fatty acids (MONO) (20:1n-9 or 22:1n-9) in the form of free fatty acids (FFA) or triacylglycerol (TAG). The average lipid digestibility for all diets measured by use of the chromic oxide method in the pyloric caeca area, midgut and hindgut were 72%, 83% and 88%, respectively, showing that lipid digestion and absorption occur mainly in the pyloric caeca area, but also extend throughout the intestinal tract. Analyses of digesta present in the intestinal segments suggest the predominance of non-specific lipolytic activity producing primarily FFA and glycerol from dietary TAG. Comparisons of the fatty acid composition of the lipid classes in the digesta showed that the utilization of dietary TAG was dependent both on the rate of release of the individual fatty acids from TAG, and their subsequent rate of absorption. When supplied as either FFA or TAG, the levels of PUFA (18:2n-6 or 18:3n-3) in the digesta were very low, indicating almost complete utilization. Both MONO used (20:1n-9 or 22:1n-9) were absorbed less efficiently than PUFA, but the rate of release from TAG seemed to be rate limiting only for 22:1n-9, which accumulated in the digesta. The rates of absorption of 20:1n-9 and 22:1n-9 when fed as FFA were the same. Comparisons of the levels of fatty acids in the dietary coconut oil TAG with those of the digesta lipids showed that 12:0 was a good substrate for intestinal lipase and was quickly absorbed. The lipolysis of 14:0 and 16:0 was intermediate while the longer-chain 18:0 appeared very resistant to digestion and was a major component of TAG, diacylglycerols and monoacylglycerols present in particularly the hindgut digesta. The absorption of 18:0 also appeared to be very low. The results suggest that PUFA are released very rapidly from dietary TAG by intestinal lipases in Arctic charr, and are specifically absorbed compared with long-chain saturated and monounsaturated fatty acids. The rate of lipolysis may be the rate-limiting step in the digestion of very long chain monounsaturated fatty acids such as 22:1n-9, while both the rate of lipolysis and absorption may be rate limiting for long-chain saturated fatty acids such as 18:0.     

Determining the consistency of thermal habitat segregation within and among Arctic charr morphotypes in Gander Lake,Newfoundland

Abstract – Otolith carbon and oxygen isotope data obtained from distinct genetic and ecological groups of lacustrine Arctic charr, Salvelinus alpinus L., from Gander Lake, Newfoundland, were used to examine hypotheses regarding the consistency of differential habitat use among the groups. Results indicated thermal habitat separation by group, with small ‘pale’ individuals consistently remaining in cooler profundal habitats and larger ‘dark’ individuals more frequently occupying warmer upper water column habitats. Theoretical measures of resource separation and competition indicated lower thermal habitat overlap among the forms and greater within‐form competition. Depth at capture data indicated more varied short‐term use of available lake habitats by ‘dark’ form Arctic charr, possibly as a result of cannibalistic foraging on profundal ‘pale’ form fish. Nominal capture depth data only partially explained observed variation in the mean temperature of occupied thermal habitat, suggesting that capture depth can only be used as a rough index of thermal habitat use. Provided that sufficient thermal gradients exist in the environments being studied, otolith oxygen isotopes provide a useful means of establishing the significance of niche differentiation among individuals.     

Thermal habitat use and juvenile growth of Svalbard Arctic charr: evidence from otolith stable oxygen isotope analyses

Abstract – Stable oxygen isotopes (δ¹⁸O) derived from otoliths were used to estimate mean annual water temperatures experienced by individual Svalbard Arctic charr, Salvelinus alpinus (L.), during their first four growth seasons. The analysed Arctic charr experienced a high variety of temperatures, indicating the use of different thermal habitats. A higher proportion of the juveniles experienced warmer temperatures during their first summer compared with later summers, suggesting the selective use of the shallowest littoral areas of the lake. Although the estimated temperatures were consistent with water temperatures found in High Arctic rivers and lakes during summer, they did not represent the annual variation in air temperature registered over the 20 years of otolith measurement. Furthermore, summer otolith increment width did not correlate with the experienced temperature. However, after the second year, otolith increment width was highly dependent on increment width during the previous summer. This study estimated mean summer water temperatures experienced by individual Arctic charr during the first four growth seasons providing additional evidence that stable oxygen isotope analysis can be used to provide insight into the thermal habitat use by juvenile Arctic charr.     

Integration of ecology,demography and genetics to reveal population structure and persistence: a mini review and case study of stream‐dwelling Dolly Varden

Abstract – Spatial structures can drive population dynamics and persistence. The roles of space and dispersal on dynamics, however, remain largely unknown in wild populations, mainly because of the difficulty in extensive/intensive field surveys at multiple locations. Here, I integrate results of ecological, demographic and genetic studies to elucidate detailed population structure and to identify the mechanisms of population persistence in a stream fish. Spatial structures, such as habitat size and connectivity, are particularly important in river and freshwater networks because such ecosystems are highly vulnerable to human activities. These issues are explored by examining results from a decadal research on the stream‐dwelling Dolly Varden charr in the Sorachi River basin, Japan. More than 100 local habitats (i.e. tributaries) were examined for spatial structure of populations by, such as, species presence, population census, redd counts, analysis of population synchrony and microsatellite DNA analysis. The results indicate that (i) population demography is largely independent in each tributary, (ii) some large tributaries support self‐sustaining populations, (iii) despite small population sizes in most tributaries (<30 spawning females), local extinction is rare, except in human‐influenced areas and (iv) probabilities of extinction are likely reduced by immigration of fish from neighbouring tributaries. The evidence suggests that Dolly Varden in this river system function as a source‐sink or mainland‐island metapopulation structure and that processes influencing these structures vary within the stream network. Overall, local populations may be highly persistent as long as local populations are well connected. I also discuss the vulnerability of stream fishes to habitat alterations.     

Ecological characteristics of ninespine stickleback Pungitius pungitius from southern Baffin Island,Canada

Abstract – Stable δ¹³C and δ¹⁵N isotopes, diet and parasites demonstrated that the prey consumed by ninespine stickleback Pungitius pungitius in a small lake on Baffin Island changed during the summer and also revealed intraspecific variation in their ecological niche. In July, there were differences in the diets of male and female ninespine stickleback as indicated by the stable isotopes, differences corroborated by the data on diet composition and the parasite fauna. Differences suggested that the sexes occupied different habitats during spawning. During July, females utilise the shallower littoral areas consuming zooplankton and benthic organisms, while males occupy deeper areas of the littoral zone feeding mainly on pelagic zooplankton. Parasite data support these observations as males had higher infections of copepod‐transmitted parasites than females. There appeared to be no segregation of resources between males and females in late August, although the diet of both male and female ninespine stickleback shifted towards more benthic organisms, compared with July. Differences in δ¹³C isotope, diet composition and infections of co‐occurring parasites demonstrated that sympatric ninespine stickleback and Arctic char Salvelinus alpinus captured in the littoral zone occupied separate niches. Ninespine stickleback preyed mainly on zooplankton and chironomids, while Arctic char consumed a greater variety of prey items, including zooplankton and larger‐sized prey such as insects and ninespine stickleback. The multifaceted approach improved our understanding of the trophic ecology of ninespine stickleback in southern Baffin Island and quantified resource use and dietary overlap with Arctic char.     

Evaluating genetic structure among resident and migratory forms of bull trout (Salvelinus confluentus) in Northeast Oregon

Abstract –  Many salmonids express multiple behavioural forms within the same population, representing an evolutionary adaptation to a heterogeneous environment. For bull trout, resident and migratory forms co-occur in streams, but it is unknown whether the two forms assortatively mate. We assessed genetic differentiation between resident and migratory bull trout (using eight microsatellite loci) in the South Fork Walla Walla River. We PIT-tagged and fin-clipped bull trout and assigned individuals to behavioural subpopulations based on movement patterns. The pair-wise F _ST value between resident and migratory subpopulations (0.0037) was statistically insignificant, and individual-based analyses of structure using both multivariate and Bayesian approaches showed a lack of genetic structure within the population. These results have important implications for assessing population status and management; while the population may be managed as a single reproductive unit, the phenotypic variation within this population may have fitness consequences and thus merits conservation.     

Are native brook charr and introduced rainbow trout differentially adapted to upstream and downstream reaches?

Abstract— Due to species introductions, brook charr (Salvelinus fontinalis) and rainbow trout (Oncorhynchus mykiss) occur together in many North American streams and typically exhibit a pattern of distribution in which brook charr numerically dominate headwaters and rainbow trout dominate downstream reaches. It has been suggested that 1) the two species compete or 2) the two species do not compete because they are differentially adapted to environmental conditions found in upstream and downstream zones. We assessed whether there were differences in growth and macrohabitat (pool, run and riffle) selection of brook charr and rainbow trout in upper, middle and lower stream zones of a small Pennsylvania stream. Brook charr and rainbow trout placed in replicate paired enclosures set in upstream and downstream reaches showed no significant differences in growth and survival rates upstream, but brook charr had significantly greater growth rates than rainbow trout downstream. Enclosed fish and free-ranging fish both had negative growth rates during the summer. Enclosed fish lost significantly less weight than free-ranging fish. Instantaneous growth rates of free-ranging adult brook charr and rainbow trout from May to August were negative for both species in all stream zones. Underwater observations of adult brook charr and rainbow trout showed both species occurred significantly more often in pool macrohabitats than expected on the basis of macrohabitat availability, except for rainbow trout in the upstream zone. The proportion of pool macrohabitat was not significantly different among stream zones. Brook charr do not appear to be better adapted to upstream environments in Powdermill Run based on growth, survival and macrohabitat selection during summer. Negative biotic interactions acting along with differential environmental adaptations may explain the pattern of distribution of brook charr and rainbow trout in streams, but long-term transplant experiments with additional life stages will be necessary to examine this hypothesis.