Diel distribution,behaviour and consumption of juvenile Chinook salmon (Oncorhynchus tshawytscha) in a Wilderness stream

Abstract – Understanding population regulation in juvenile salmonids requires distinguishing the effects of intrinsic (size, behaviour) and extrinsic (food, competition) factors. To examine the relative influence of these variables on juvenile Chinook salmon (Oncorhynchus tshawytscha) in the Salmon River drainage (ID, USA), we examined diel differences in foraging microhabitats, behaviour and consumption in two areas with consistent differences in parr‐to‐smolt survival. In lower Big Creek (LBC, high‐survival area) and upper Big Creek (UBC, low‐survival area), we observed fish by snorkelling, recording length, behaviour (foraging rate and aggression) and physical (depth, velocity, cover, temperature) and biotic (density, size and species of neighbouring fish) microhabitat features. Stomach contents were extracted to estimate consumption. Depth and temperature were greater in LBC, where Chinook salmon were significantly larger and present at lower densities. Fish in LBC exhibited higher foraging activity during the day than night, but there were no size differences between day and night foragers. In UBC, a higher density area, foraging behaviour did not change between day and night, although the smallest size classes did not forage nocturnally. Regression models that integrated physical and biotic variables suggested that physical factors influenced foraging in both areas, but competition also affected foraging in UBC. Our results demonstrate that fish from low‐ and high‐survival populations in Big Creek are exposed to different physical and biological influences during their first growth season, which are reflected in different diel foraging behaviours.     

澳洲长鳍鳗染色体组型的初步研究

以澳洲长鳍鳗(Anguilla reinhardtii)头肾组织为材料,采用腹腔注射植物血细胞凝集素(PHA)、秋水仙素和空气干燥法制备染色体标本,进行染色体组型分析.结果显示:澳洲长鳍鳗染色体为38条,核型公式为2n=14m+6sm+18t,NF=58;未发现随体、次级缢痕及异形染色体.     

Seasonal differences in the diel movements of Macquarie perch (Macquaria australasica) in an upland reservoir

Knowledge of the movement patterns of threatened fishes aids their conservation management and informs sustainable development of natural resources including freshwater. Prior to the expansion of a temperate upland reservoir in Australia, we used radio telemetry to compare seasonal differences in the diel movements of adult endangered Macquarie perch (Macquaria australasica) (235–414 mm total length) in Cotter Reservoir, Australian Capital Territory. Macquarie perch exhibited a diel range of 389 ± 46 m, a diel mobility of 769 ± 93 m and diel area use of 24008 ± 5595 m² among four seasons. Diel range was significantly higher in winter compared with other seasons, and diel mobility was negatively correlated with fish size among four seasons. Macquarie perch inhabited deeper water in summer across the diel cycle (7.2 ± 0.5 m) in comparison with other seasons (spring: 3.8 ± 0.3 m, autumn: 3.0 ± 0.2 m, winter: 3.0 ± 0.3 m). Within seasons, both remote and manual telemetry identified that diel activity was predominantly crepuscular. Prey availability and the threat of avian predation represent the most likely explanations for the differences in seasonal movements. In a reservoir where expansion will likely result in a loss of critical habitat (emergent macrophytes) for this endangered species, we use site‐specific knowledge of the spatial ecology of Macquarie perch to inform the placement of shelter habitat prior to filling the enlarged reservoir.     

Movements of the European eel (Anguilla anguilla) in a chalk stream

Abstract – The movements of wild European eels (Anguilla anguilla L.) were monitored continuously over a 2‐year period in a tributary of the River Itchen, Hampshire, UK, using a passive integrated transponder (PIT) antenna system. The time of these movements was then related to a number of monitored and calculated environmental parameters. No eel movements were recorded in the winter months when mean stream temperature was below 10 °C. The numbers of movements peaked in May, when mean water temperatures and day length were increasing. The movement of eels was significantly (P < 0.001, R² = 0.45, N = 72) correlated with the time of sunset, with the majority (72%) recorded during the hours of darkness. The results of this investigation have implications for the design/timing of surveys of yellow eel populations and their habitat associations and suggest that successfully determining the microhabitat preferences of active resident eels will require remote monitoring throughout the 24‐h period.     

The use of clove oil as an anaesthetic for the longfinned eel, Anguilla reinhardtii (Steindachner)

To handle large river eels during procedures such as measuring and tagging for field and aquaculture studies, they must be anaesthetized. During our initial biological studies of Anguilla reinhardtii (Steindachner) it was found that the anaesthetic benzocaine was relatively expensive and elicited a variable response, even when used at relatively high concentrations. Human health risks are also a concern when using benzocaine, as some of the eels may later be sold for human consumption. Therefore, experiments were done to evaluate the use of clove oil (a safe, naturally occurring product) for anaesthesia of this species at a range of temperatures (17 and 25 °C) and salinities (0–32 g L^?1). It was found that clove oil provided a suitable anaesthetic response through this wide range of temperatures and salinities. Response times were found to be relatively variable for both benzocaine and clove oil. This variability may be related to stress, environmental factors, or the condition of the fish. Clove oil is recommended for anaesthesia of anguillid eels because it is effective, relatively inexpensive, and poses little risk to human health.     

Habitat utilization and diel behavior of juvenile bull trout (Salvelinus confluentus) at the onset of winter

Abstract— Underwater observations were used to describe habitat use and diel behavior of juvenile bull trout ( Salvelinus confluentus ) at the onset of winter (0.8°C) in a second-order central Idaho stream. All fish observed during daytime counts were concealed beneath "home stones" (mean dimensions 32.3 by 21.9 cm) in primarily pool and run habitats. Focal point depths and velocities averaged 57.2 cm and 4.7 cm/s (home stone removed). Fish maintained stations over substrate with low percentages of fine (< 2 mm, mean= 5.2%) sediment. Concealed bull trout were not evenly distributed across the stream channel. Significantly more home stones were distributed near the midline of the channel, compared to the channel margins. Fish size was positively correlated with home stone size. At night, bull trout exhibited a diel behavioral shift, some fish moved out of daytime concealment cover into the water column. At night, bull trout were observed feeding and resting, primarily in pool and run habitats. During both day and night, bull trout used riffles significantly less frequently than those habitats were available.     

First isolation of Flavobacterium psychrophilum associated with reports of moribund wild European eel (Anguilla anguilla) in Scotland

In late April 2015, the River Dee Trust informed Marine Scotland Science, Fish Health Inspectorate (FHI), that there had been observations of dead and moribund European eels on the River Dee. Later in May, the Spey Fishery Board also reported a number of moribund European eels in a rotary screw smolt trap on the River Spey. In total, 10 cases involving moribund eels were investigated in 2015 and one case in 2016. In addition, a health screen was conducted to investigate the potential presence of Flavobacterium psychrophilum in healthy eels and Atlantic salmon from the River Dee in 2015. Externally, the diseased eels demonstrated white patches in different locations of the body. In all cases, F. psychrophilum was detected by bacterial isolation and/or molecular methods. Three isolates were further characterized by whole‐genome sequencing (WGS) as belonging to sequence type 15 (ST15). Histological examination of diseased European eels revealed lesions at the level of the integument. The pathogen screen for F. psychrophilum in wild healthy fish tested negative by PCR. Further investigation is required to understand the pathogenicity of this bacterium on the health of eels and the potential impact on the wild salmonid population.     

Influence of geomagnetism on the activity and orientation of the eel, Anguilla anguilla (L.), as evident from laboratory experiments

Abstract– Studies were performed with both a mechanical and a photosensory arrangement of the experimental tanks. Silver (migratory) eels were more active than yellow (stationary) eels. Comparison of pooled data on yellow eels tested under natural geomagnetic field conditions with those on eel tested under unnatural ones prcded no evidence of difference in activity. Silver and yellow eels showed stronger activity during the 6 days around new moon compared with the phase around full moon as well as a peak before new moon and a smaller peak before full moon. Under each kind of unnatural field condition, the activity relationships reversed or were cancelled. The directional choice of eels under natural conditions (controls) pointed to magnetic NW and mostly also in the opposite direction. When the magnetic north was changed by 90°, the tested yellow eels followed this change to about the same degree. The additional change of both the inclination (from 68° or 45° or 30°) and total intensity (by a reduction to 31% of the natural field) resulted in a change of the preferences of about 90° relative to magnetic north. Reversal of magnetic north by 180°, which is identical to a change of the inclination from 68° to 112°, also resulted in a change of the preferences by about 90°. Three experiments using compensation of both the horizontal and the vertical geomagnetic field led to circular directional preferences at random in two cases and in one case to about NW of the residual field magnetic north. The navigational abilities of the eel, on the basis of its magnetic sensitivity, are discussed.     

Prey selectivity and diel feeding chronology of juvenile chinook (Oncorhynchus tshawytscha) and coho (O. kisutch) salmon in the Columbia River plume

We studied salmon feeding selectivity and diel feeding chronology in the Columbia River plume. Juvenile chinook and coho salmon were caught by trawling at 2–3 h intervals throughout a diel period on three consecutive days (21–23 June 2000) at stations located 14.8 and 37 km offshore from the mouth of the Columbia River. A total of 170 chinook salmon were caught at the inshore and 79 chinook and 98 coho salmon were caught at the offshore station. After each trawl, potential prey were sampled at different depths with 2–3 different types of nets (1‐m diameter ring net, bongo net, neuston net). Despite the variability in zooplankton abundance, feeding selectivity was surprisingly constant. Both salmon species fed selectively on larger and pigmented prey such as hyperiid amphipods, larval and juvenile fish, various crab megalopae, and euphausiids. Hyperiid amphipods were abundant in the salmon diets and we hypothesize that aggregations of gelatinous zooplankton may facilitate the capture of commensal hyperiid amphipods. Small copepods and calyptopis and furcilia stages of euphausiids dominated the prey field by numbers, but were virtually absent from salmon diet. Juvenile chinook salmon, with increasing body size, consumed a larger proportion of fish. Stomach fullness peaked during morning hours and reached a minimum at night, suggesting a predominantly diurnal feeding pattern. In general, both chinook and coho salmon appear to be selective, diurnal predators, preying mostly on large and heavily pigmented prey items, in a manner consistent with visually oriented, size‐selective predation.     

Interactions between fishing strategies of Nephrops trawlers in the Bay of Biscay and Norway lobster diel activity patterns

Abstract  Norway lobster, Nephrops norvegicus (L.), in the Bay of Biscay exhibited diel activity patterns with more individuals outside their burrows at dawn and dusk, increasing catchability at these times. Data from an on board observer programme on Nephrops trawlers between 2002 and 2005 were used to assess variability in catchability in commercial catches. Catch numbers per haul varied spatially and between months, but no signal for diel variations was found. Fishing strategies developed by the Nephrops trawlers had several components. On a seasonal level, they started around sunrise. On a haul level, haul duration decreased from haul to haul, with the longest hauls taking place at the time of the highest catchability. By-catch of hake, Merluccius merluccius (L.), increased more than proportionally with haul duration.     

Modelling daily catches of silver-phase European eel (Anguilla anguilla) in two hydropower-regulated rivers

Estimation of silver eel production, Anguilla anguilla L., is fundamental for the management of eel stocks. In the hydropower-regulated rivers Shannon and Erne, Ireland, production is calculated using catch data from a conservation trap and transport programme. However, in both rivers gaps in silver eel catch datasets tend to occur, which can lead to biases in production estimates. Generalised additive models (GAMs) were used to model daily catch in these rivers based on a variety of environmental variables. Final models for the Shannon and Erne explained 83.7% and 78.8% of deviance in daily catch, respectively. A second model on the Erne included catch from a nearby fishing site in an attempt to increase explanatory power and explained 91.7% of deviance. Although model accuracy was increased, reliance on catch from another site may limit the applicability of the model. Model predictions were combined with estimates of fishing efficiency to predict production for the Shannon (36,210 kg; 0.85 kg/ha) and Erne (66,899–67,047 kg; 2.55–2.56 kg/ha). These values represented a 9.3% and 2.8%–3.0% increase on production estimated from incomplete catch records alone for the Shannon and Erne, respectively.     

Using acoustic telemetry and snorkel surveys to study diel activity and seasonal migration of round goby (Neogobius melanostomus) in an estuary of the Western Baltic Sea

In just two decades, round goby Neogobius melanostomus (Pallas) has dispersed throughout most of the Baltic and the North American Great Lakes. It thrives in shallow sheltered areas, where it is impacting native fauna. In Denmark, researchers, governmental institutions and fishers have joined in an effort to establish a sustainable round goby fishery. To do so, basic information about the movement of round goby is essential, so the movements of 50 round gobies were tracked using acoustic telemetry. The results revealed that activity took place mainly at night and seasonal migrations were common. The most frequent migration behaviour observed was a seaward return migration during winter, which was further confirmed by a snorkel survey. Tracking data also revealed riverine upstream dispersal. The results demonstrate that the round goby can be mapped using telemetry, and it is suggested that fishing for round goby may improve efficiency by targeting seasonal migration corridors.     

Haemoglobin powder as a dietary fish meal replacer in juvenile Japanese eel, Anguilla japonica (Temminck et Schlegel)

Two consecutive 6-week feeding trials were conducted to determine the amount of haemoglobin powder (BM) that could replace fish meal (FM) in juvenile Japanese eel Anguilla japonica (Temminck et Schlegel) diets. Fish were fed 50% crude protein diets in which each of ten isonitrogenous diets was formulated to contain white fish meal and/or blood meal as the dietary protein source to replace FM by BM as follows: Diet 1 (control), 0% BM; diet 2,12.5% BM; diet 3,25% BM; diet 4, 50% BM; diet 5, 75% BM; diet6,100%BM;diet7,25%BM + 3 Essential Amino Acids (EAA); diet 8, 50% BM + 3 EAA; diet 9, 75% BM + 3 EAA; diet 10, 100 BM + 3 EAA. In the first 6-week period, the results were not consistent with the treatments, and poor adaptation of the fish to the experimental diets and conditions was observed. In the second 6-week period, weight gain, specific growth rate, protein efficiency ratio and protein productive value offish fed diets 2, 3, 4, 7, 8 and 9 were not significantly different from those of fish fed the control diet (P > 0.05). However, feed conversion ratios offish fed diets 6 and 10 were lower than that offish fed the control diet (P < 0.05). These results demonstrate that FM can be replaced by BM up to 50% without supplementation of three EAA, and up to 75% with three EAA supplementation in juvenile Japanese eel diets.     

Size-related habitat use by bitterling (Rhodeus sericeus) in a regulated lowland river

Abstract  – Habitat use by four size-classes of bitterling ( Rhodeus sericeus ) in a regulated lowland river was studied at two spatial scales. Mesohabitat scale was represented by the bank type (boulder, beach and steep eroded bank). Microhabitat associations with substrate types, vegetation, woody debris and position in the stream were examined at each mesohabitat scale. Three size cohorts of young-of-the-year (0+) fish and a group of adult bitterling were detected. Univariate ( χ ²-tests) and multivariate (Outlying Mean Index analysis) methods were applied to determine size-related habitat associations. All the size-classes of bitterling avoided the steep eroded bank and most 0+ bitterling were distributed along the boulder bank. The smallest fish had the most pronounced habitat requirements and occurred mostly in the depositional areas, whereas the larger 0+ fish occurred in deeper water. The size-related change in the habitat use coincided with a change in diet and morphological state.     

人工诱导花鳗鲡的精巢发育成熟及其精子的生物学特性

用肌肉注射HCG的处理方式（剂量为500U/㎏•体重,每周注射1次,注射时间为6周）诱导雄性花鳗鲡性腺发育成熟,成熟率达80.0%。对人工催熟花鳗鲡精子的生物学特性研究结果表明：花鳗鲡精子头部长径为3.81±0.69µm,短径为1.24±0.15µm;尾部长度为24.83±3.05µm;精液pH为7.3~7.5,精子密度为1.02×1010尾/ mL。精子的适宜盐度为15~20,其中盐度为15时,精子激活比率最高,快速运动时间以及精子的寿命最长。精子的pH适宜范围为6.0~8.0,pH值过高或过低都会影响精子的活力与寿命。另外,4 种金属离子(Mg2+、Ca2+、Na+和K+)对花鳗鲡精子活力与寿命的影响趋势基本一致,金属离子浓度过高或过低都会抑制精子的活力、缩短快速运动时间和寿命。而MgCl2、CaCl2、KCl、NaCl溶液浓度为0.4~0.6g/mL时,精子活力最好,最高激活比率为3级（41.0%~60.0%）。     

Effects of non-native brook trout (Salvelinus fontinalis) on threatened juvenile Chinook salmon (Oncorhynchus tshawytscha) in an Idaho stream

Macneale KH, Sanderson BL, Courbois J-YP, Kiffney PM. Effects of non-native brook trout ( Salvelinus fontinalis ) on threatened juvenile Chinook salmon ( Oncorhynchus tshawytscha ) in an Idaho stream.
Ecology of Freshwater Fish 2010: 19: 139–152. © 2009 John Wiley & Sons A/S
Abstract –  Non-native fishes have been implicated in the decline of native species, yet the mechanisms responsible are rarely apparent. To examine how non-native brook trout may affect threatened juvenile Chinook salmon, we compared feeding behaviours and aggressive encounters between these sympatric fish in Summit Creek, Idaho. Snorkelers observed 278 focal fish and examined diets from 27 fish in late summer 2003. Differences in feeding behaviours and diets suggest that there was minimal current competition for prey, although individual Chinook feeding activity declined as their encounter rate with other fish increased. While difference in size between fish generally determined the outcome of encounters (larger fish 'winning'), it was surprising that in some interspecific encounters aggressive Chinook displaced slightly larger brook trout (≤20 mm longer). We suggest that in late summer, frequent intraspecific interactions may be more important than interspecific interactions in potentially limiting Chinook growth in Summit Creek and perhaps in other oligotrophic streams where they co-occur.     

Diurnal and nocturnal movements of river blackfish (Gadopsis marmoratus) in a south-eastern Australian upland stream

Abstract –  We used radio-telemetry to investigate the movement patterns of river blackfish [ Gadopsis marmoratus (Richardson)] in Armstrong Creek, south-eastern Australia between August and October 2005. Movements of 11 fish were monitored 2–3 times per week during daylight over 48 days and diel movements of six fish monitored hourly for three consecutive days and nights. Most river blackfish displayed little or no movement during the day and were confined to distinct positions in the stream. However, fish moved over significantly larger ranges and moved amongst mesohabitats at night, which would not have been detected using daylight tracking data only. River blackfish most often were located within pools, but they also commonly used riffle and run habitats. We also found that several fish used inundated riparian areas during a flood and two fish made rapid, large movements coinciding with the elevated flows. This study has revealed previously undocumented aspects of the movements and behaviour of river blackfish. The study has also shown the potential for different conclusions regarding the extent of movement by a species depending on the temporal scale and the timing of observations.     

Foraging behaviour of juvenile pink salmon (Oncorhynchus gorbuscha) and size‐dependent predation risk

Two hypotheses related to effects of juvenile pink salmon (Oncorhynchus gorbuscha) foraging behaviour and size on their predation risk were evaluated using field data collected in Prince William Sound, Alaska 1 995–97. My results supported the hypothesis that low macrozooplankton density leads to dispersion of juvenile salmon from shallow nearshore habitats and greater predation risk, but zooplankton type was an important factor. When the biomass of large copepods (primarily Neocalanus spp.) declined, salmon dispersed from shallow nearshore habitats, and mean daily individual predator consumption of salmon increased by a factor of 5. A concomitant five‐fold increase in the probability of occurrence of salmon in predator stomachs supported the notion that increased predation on salmon was caused by a greater overlap between predator and prey when salmon dispersed offshore, not an increase in the number of salmon consumed per feeding bout. The results also generally supported the hypothesis that the timing of predation events modifies the nature of size‐dependent predation losses of salmon to different predator groups (small and large planktivores and piscivores). Size‐dependent vulnerabilities of salmon to predators were a function of both predator and prey sizes. When simulated predation was shifted from May to June, the vulnerability of salmon became more dependent on their growth than initial size. But, the size‐ and growth‐dependent vulnerabilities of salmon differed more among predator groups than between May and June, suggesting that changes in the composition of predator fields could more strongly affect the nature of size‐dependent predation than changes in the timing of predation losses.     

花鳗鲡AQP3基因的分子特征及其应对盐度变化的表达规律

为了探究花鳗鲡(Anguila marmorata)AQP3基因在不同盐度下的表达规律,利用RACE技术克隆了花鳗鲡AQP3基因c DNA全长序列,并进行了生物信息学分析;通过实时荧光定量PCR(RT-q PCR),检测了花鳗鲡AQP3在9个组织中的分布及盐度胁迫后鳃、肾、肠组织在0、6、12、24 h和3、5、10 d的表达情况。结果显示:花鳗鲡AQP3基因的c DNA全长为1299 bp,开放阅读框(ORF)为891 bp,5’非编码区(UTR)和3’非编码区(UTR)分别为60 bp和348 bp,共编码296个氨基酸,具有6段跨膜结构域及2个NPA(天冬氨酸-脯氨酸-丙氨酸)保守结构域。氨基酸多重序列比对结果显示,花鳗鲡AQP3基因与其同属的欧洲鳗鲡(Anguilla anguilla)、日本鳗鲡(Anguilla japonica)同源性分别高达97.0%和96.0%。RT-q PCR检测发现,AQP3基因在鳃组织中表达量最高,而在脾脏中表达量最低;在咸淡水(盐度10)和海水(盐度25)组中,鳃组织的AQP3基因表达水平呈下降趋势,且在各时段均显著下调;肾组织的AQP3表达水平在咸淡水(除24 h外)和海水(除6 h外)组中也显著下调;肠组织的AQP3表达水平在咸淡水组中显著上调,而在海水组中则显著下调。研究表明,花鳗鲡AQP3的mRNA表达量在应对不同盐度环境时呈现不同的表达变化模式,这将为深入揭示花鳗鲡适应盐度变化的分子调控机理奠定理论基础。