Density‐ and species‐dependent errors in single‐pass timed electrofishing assessment of riverine salmonids

Electrofishing techniques are widely used for the estimation of the size of stream‐dwelling fish populations for both fishery management and scientific study. In contrast to multiple pass, population depletion methods, single‐pass catch‐per‐unit‐effort (CPUE) methods are less time‐consuming and labour‐intensive. A possible issue with the commonly used fixed total time CPUE protocol is that it does not differentiate between the time spent actively fishing and the time incurred while not actively fishing (e.g. removing fish from nets and navigating the site). This issue is likely related to fish density. This study compared two methods of CPUE electrofishing and tested the hypothesis that time spent handling fish and navigating a site can be a source of error in the commonly used fixed total time electrofishing method. Seventy‐one sites were sampled across three subcatchments in the Foyle catchment in Northern Ireland. We found a difference in the catch per unit time between the two methods and that this difference increased with fish density. The fixed‐time CPUE method also failed to detect a species presence in low‐density sites.     

Entry of adult Atlantic salmon into a tributary of the Aberdeenshire Dee,Scotland

Upstream counts of adult salmon in a tributary to the River Dee during autumn and winter were examined over a 13‐year period using an optical fish counter. Statistical analysis indicated that salmon were mainly primed to enter the tributary at a particular time of year, peaking at early December. However, environmental factors also had a large influence. Entry of salmon was initiated by high flow rates in the main stem of the River Dee. Increases in water level in the tributary itself were not needed to stimulate the entry of salmon. Moreover, a change in flow from 1 day to the next did not result in a response from salmon. Rather, they reacted only after more than a day of flow increase. There was no consistent threshold level of flow that triggered tributary entry. The upstream passage of salmon was reduced at low temperatures (below 3°C). The numbers of salmon migrating upstream showed a gradual increase as the temperatures increased up to 11°C, and then sharply decreased at higher temperatures. Female salmon migrated earlier by about 2 weeks on average than males. Increasingly, counters and traps are being installed on spawning tributaries to examine the state of salmon stocks. Caution should be exercised, however, in using upstream entry data from individual tributaries to provide an overall assessment of salmon abundance, as local conditions in the tributaries may affect the salmon counts in particular years.     

Effects of tagging on migration behaviour,survival and growth of hatchery‐reared Atlantic salmon smolts

The effects of four different tagging methods (PIT, anchor T‐tag, Carlin tag and dummy radio transmitter) on survival, behaviour and growth of Atlantic salmon smolts during their downstream migration were examined in semi‐natural circular channels during a natural migration period in spring. Survival of smolts was high and tagging wounds healed well in all tagging groups. Tag loss rates were generally low, being the highest (2.5%) in the dummy radio transmitter group. Total length and body mass of the tagged and untagged smolts did not differ at the end of the experiment. Migration activity of smolts generally showed similar patterns among the treatments. However, Carlin‐tagged smolts started their migration slightly later than the PIT‐tagged fish, and smolts tagged with Carlin tag or dummy radio transmitter showed less overall migration activity than fish with PIT tag.     

大西洋鲑循环水养殖水体异养细菌组成的研究

采集养殖池水样,选取Zobell 2216E琼脂培养基、溶菌肉汤琼脂培养基、硫代硫酸盐柠檬酸盐胆盐蔗糖琼脂培养基、脑心浸液琼脂培养基、胰蛋白胨大豆琼脂培养基、营养琼脂培养基6种常见固体培养基进行细菌分离培养,以平板菌落计数法和菌落外观形态特征辨别及16SrRNA基因测序方法进行异养菌计数和种类组成分析。结果显示:(1)养殖池水体异养菌可分为4大类,分别属于变形菌门(包括α-、γ-变形菌纲)、厚壁菌门、拟杆菌门、放线菌门,其中以γ-变形菌纲为优势菌群。按属分类大多为假交替单胞菌属和弧菌属。(2)不同培养基分离菌落数量2216E培养基溶菌肉汤琼脂培养基胰蛋白胨大豆琼脂培养基脑心浸液琼脂培养基营养琼脂培养基硫代硫酸盐柠檬酸盐胆盐蔗糖琼脂培养基,且2216E培养基菌落数极显著高于其余5种培养基(P0.01);2216E培养基所分离细菌的种类最多,分属于12个属,假交替单胞菌属为优势类群,占比50%,弧菌属仅占3.13%;脑心浸液琼脂培养基、溶菌肉汤琼脂培养基、胰蛋白胨大豆琼脂培养基所分离细菌均以弧菌属为优势菌群,分别占33.33%、60%、25%;硫代硫酸盐柠檬酸盐胆盐蔗糖琼脂培养基所分离细菌仅分属于1个属,即弧菌属;营养琼脂培养基无弧菌,但有假单胞菌分离出。     

Development and application of molecular methods (PCR) for detection of Tasmanian Atlantic salmon reovirus

Molecular (PCR) diagnostic tests for the detection and identification of aquareovirus in general, and Tasmanian Atlantic salmon reovirus (TSRV) specifically, were developed, and their diagnostic sensitivity and specificity were determined and compared with virus isolation in cell culture. Intralaboratory and interlaboratory comparison of PCR (conventional hemi‐nested RT‐PCR & RT‐qPCR) and virus isolation in cell culture using finfish cell lines, CHSE‐214 and EPC, was carried out for the detection and identification of TSRV using field samples of farmed Atlantic salmon Salmo salar, L. from various aquaculture sites around Tasmania. The interlaboratory comparison of diagnostic methods was carried out between two laboratories, AAHL‐CSIRO and DPIPWE‐Tasmania. A total of 144 fish from nine sites (12–33 fish per site) were sampled from two regions of Tasmania (Tamar River estuary in the north and Huon River estuary in the south‐east) during late spring to early summer of 2009, and the data were analysed using different statistical approaches. The prevalence of TSRV ranged from 6% to 22% in both regions. All the diagnostic methods (data from both laboratories) had high specificity, while the estimated sensitivity varied between tests with RT‐qPCR being the most sensitive (95.2%) method followed by virus isolation and then conventional hemi‐nested RT‐PCR.     

杀鲑气单胞菌对大西洋鲑游泳行为和血细胞数量的影响

为探讨利用鱼类行为及血细胞数量变化预警杀鲑气单胞菌(Aeromonas salmonicida)病害发生的可行性,监测了生产中感染杀鲑气单胞菌的大西洋鲑(Salmo salar L.)的游泳行为,以及杀鲑气单胞菌攻毒后大西洋鲑血细胞数量的变化。实验采用同一养殖基地和同一批次的大西洋鲑,其中现场实验鱼选自生产车间健康的和感染杀鲑气单胞菌的养殖鱼,攻毒实验中处理组实验鱼每尾背肌注射100μL、浓度为3.05×107CFU/m L的菌液,对照组注射等体积灭菌生理盐水。现场实验表明,感染杀鲑气单胞菌的大西洋鲑临界游泳速度较健康鱼低26.7%(P0.05),摆尾频率与游泳速度的线性回归方程的斜率也存在显著差异(P0.05)。攻毒实验表明,从攻毒的第4天开始,处理组大西洋鲑白细胞、淋巴细胞、单核细胞和粒细胞数量较对照组均发生显著变化,其中第6天的变化最为显著,白细胞总数、粒细胞数分别降低了2.8%和43.9%(P0.05),淋巴细胞数及单核细胞数分别升高了63.3%和23.9%(P0.05),且处理组4种血细胞数随时间呈现显著的线性变化(P0.05)。研究结果表明通过监测大西洋鲑游泳行为(临界游泳速度和摆尾频率)以及血细胞相关指标的变化可快速判断其健康状况,为病害的早期预警提供依据。     

Environmental threats and conservation implications for Atlantic salmon and brown trout during their critical freshwater phases of spawning,egg development and juvenile emergence

Atlantic salmon Salmo salar L. and brown trout Salmo trutta fario L. are species of high socio-economic and ecological value. Declining populations make them target species of fisheries management. This paper reviews the direct effects of deficient longitudinal connectivity, changes in discharge, high water temperatures, oxygen depletion, changes in water chemistry and increasing loads of fine sediment on the critical life stages of spawning, egg incubation and emergence. It further provides an overview about the basic autecological requirements of Atlantic salmon and brown trout and summarises important thresholds of physico-chemical tolerances. This collection of information provides important baselines for assessing historical, ongoing and new threats relevant for the management of both species in fresh waters. Critical early-life stages of both species are almost identical, creating synergies in conservation and restoration. Seaward-migrating forms are exposed to further stressors, but improving starting conditions can also greatly improve their resilience.     

Dietary phosphorus does not reduce the risk for spinal deformities in a model of adjuvant‐induced inflammation in Atlantic salmon (Salmo salar) postsmolts

Inflammation is a non‐specific protective mechanism towards injury known to affect bone remodelling. This study aimed to investigate the effect of Freund’s complete adjuvant (FCA) induced‐inflammation on the prevalence of spinal deformities of Atlantic salmon postsmolts fed with two different dietary P levels. Sextuple groups of salmon postsmolts were fed with either a low‐phosphorous (6 g kg^?1 available P, LP) or a high‐phosphorous (9 g kg^?1 available P) diet for a period of 101 days. On Day 102, individually tagged fish were subjected to (i) single injection with FCA (0.125 mg kg^?1 BW) dissolved in phosphate‐buffered saline (PBS) (ii) placebo injection with PBS or (iii) sham injection (insertion of needle only) or (iv) remained untreated. On Day 103, fish were given a common diet for 174 days in seawater. No significant differences in body weight were observed. Injected fish, particularly the FCA group, had more compressions in the injection site than untreated fish. No effect of diet and no interaction between treatment and diet were observed. Severe scoliosis was observed in ～7% of FCA‐injected individuals, corresponding to a mixture of bone malformations in the tail region. In conclusion, experimentally induced inflammation may be an independent risk factor for bone deformities in Atlantic salmon.