Incidence and timing of wild and escaped farmed Atlantic salmon (Salmo salar) in Norwegian rivers inferred from video surveillance monitoring

Run timing of escaped farmed Atlantic salmon Salmo salar vs. wild fish was compared by the use of video camera surveillance in 15 rivers over several years, covering 1600 km of the Norwegian coastline (from 58°N to 69°N). Annual runs of wild salmon varied among rivers from <200 fish to more than 10 000. During the surveillance period that for most rivers extended from late May to early October, larger‐sized salmon (fish ≥ 65 cm) generally entered the rivers earlier than small fish. The percentage of salmon identified as escaped farmed fish ranged from 0.1% to 17% across rivers with an average of 4.3%. Estimates of escapees are, however, assumed to represent minimum values because an unknown number of farmed fish passing the video cameras may have been misclassified as wild fish. By the use of a linear mixed model and generalised additive mixed models, it was found that the relationship between run timing and fish length differed significantly between farmed and wild salmon. While small‐sized farmed and wild fish (<65 cm) entered the river at about the same time, wild large salmon returned on average 1–2 weeks earlier than similarly sized escapees. The proportion of large‐sized farmed escapees also increased until late August and decreased thereafter. In contrast, there was a relatively constant and lower proportion of small‐sized escapees throughout the season. Within the surveillance period, there was no evidence of any exceptionally late runs of fish classified as escaped farmed salmon.     

荆江航道整治工程中透水框架集鱼效果初步评估

为了解荆江航道整治工程中透水框架的集鱼效果,分别于2014年5-6月和2015年5-6月,采用科学探鱼仪SIMRAD EY60和双频识别声纳(DIDSON)ARIS EXPORER 1800两种水声学设备,分别对荆江瓦口子水道的金城洲和太平口水道的腊林洲透水框架水域的鱼类分布情况进行了水声学监测,并对工程江段的鱼类进行了刺网调查。结果显示:采用刺网捕获鱼类17种共204尾,其中数量和重量最多的都是鳊鱼,分别占64.71%和39.62%。渔获物体长范围是10~80 cm,平均体长是(26.90±8.82)cm;EY60监测到腊林洲工程区鱼的数目是金城洲工程区的1.92倍,DIDSON监测腊林洲工程区鱼的数目是金城洲工程区的2.36倍;EY60监测到金城洲鱼类体长集中在5~10 cm,占55.24%,腊林洲鱼类体长集中在30~50 cm,占45.38%。结果表明,透水框架群对于鱼类具有一定的诱集效果。     

Consumer perception versus scientific evidence of farmed and wild fish: exploratory insights from Belgium

The increasing number of marketable fish being supplied from aquaculture is a response to the increasing demand for healthy food and is filling the gap left by depleting natural fish stocks. Little is known about the awareness and perception of the consumer in terms of farmed fish versus fish from capture fisheries. The consumer's subjective point of view is of overriding importance for the production system and product acceptance as well as for future market success. In this paper consumer perception in Belgium is explored and compared against scientific evidence of farmed versus wild fish. Primary data were collected through a consumer survey (April 2003) and focus group discussions (May 2004) with Belgian consumers. The majority of the consumer sample reported no perceived differences between farmed versus wild fish. However, mean perception scores were slightly in favour of wild fish on the attributes taste, health and nutritious value, in particular among consumers aged 55 years and older. The availability of farmed fish was perceived to be better than that of wild fish, while the consumer's perception of safety did not differ between farmed and wild fish. The focus group discussions indicated that consumers’ opinions and beliefs about farmed fish are mainly based on emotion and image transfer from intensive terrestrial livestock production rather than on awareness and factual knowledge of aquaculture.

High incidence of death due to collision of hatchery-reared Pacific bluefin tuna Thunnus orientalis juveniles in sea cages, as revealed by head and spinal injuries

High mortality of hatchery-reared Pacific bluefin tuna (PBT) juveniles is frequently observed in sea cages after transfer from indoor tanks, and is likely due to collisions of the fish with the net wall of the sea cages. Because collisions frequently cause bone injuries due to physical impact, such injuries can be considered an index of obvious collisions. In the present study, bone injuries of dead juveniles were investigated in order to examine the prevalence of net collision as a cause of death among hatchery-reared PBT juveniles in sea cages. Juvenile PBT were reared in sea cages for 90 days after transfer, and dead fish were collected and examined by the clearing and staining method or by dissection to detect injury to the vertebral column and parasphenoid. The prevalence of injuries to the vertebral column and parasphenoid until day 30 after transfer was low (0.0–12.0 %) when the fish were 5.5–15.2 cm in total length (TL). However, it drastically increased to 17.8–78.0 % for fish 21.0–39.2 cm TL from day 31 onward after transfer. These results suggest that the mortalities of juvenile PBT larger than 20 cm TL in cages were induced by net collisions.     

Behaviour of rainbow trout, Salmo gairdneri Richardson, in marine cages

Abstract. Underwater television was used to observe the distribution and swimming behaviour of groups of farmed rainbow trout, Salmo gairdneri Richardson, in marine net cages. Undisturbed rainbow trout (mean total length 240 mm) aggregated near the surface, remaining motionless in slack water and formed polarized shoals at higher current velocities. Larger fish (mean total length 317 mm) occupied deeper parts of the cage and were more active during periods of slack water. The results are compared with previous work on farmed Atlantic salmon, Salmo salar L., and discussed in relation to the biology of wild rainbow trout and recent work on exercise, growth and condition in salmonids.     

Automatic Bluefin Tuna (Thunnus thynnus) biomass estimation during transfers using acoustic and computer vision techniques

In this work, acoustic and computer vision techniques are combined to develop an automatic procedure for biomass estimation of tuna during transfers. A side scan sonar working at 200 kHz and a stereo camera, positioned facing towards the surface to record the ventral aspect of fish, are set as acquisition equipment. Moreover, a floating structure has been devised to place the sensors between cages in transfers, creating a transfer canal that allows data acquisition while fish swim from donor to receiving cage. Biomass assessment is computed by counting transferred tuna and sizing a representative sample of the stock. The number of transferred tuna is automatically deduced from acoustic echograms by means of image processing techniques, whereas tuna size is computed from the stereo videos using our automatic computer vision procedure based on a deformable model of the fish ventral silhouette. The results show that the system achieves automatic tuna counting with error below 10%, achieving around 1% error in the best configuration, and automatic tuna sizing of more than 20% of the stock, with highly accurate Snout Fork Length estimation when compared to true data from harvests. These results fulfil the requirements imposed by International Commission for the Conservation of Atlantic Tunas for compliant transfer operations.     

网箱养殖鱼类柔性分级系统的试验研究

根据对网箱养殖许氏平 (Sebastesschlegeli)的生物学测定 ,得到其体重与体宽的回归方程为 :W =0 115 7L2 .190 6 ,R2 =0 92 6 6 ,并以其体宽为分级系统格栅间距确定的依据。在 4m× 4m×4m网箱内使用间距为 4 4mm的分离栅经过 10min分级 ,结果表明 ,允许被分离的小个体鱼类的平均分级率为 90 33% ;使用间距 4 4mm的分离栅在周长为 5 0m的网箱中分级后 ,分级网内大个体鱼类的体重比分级前平均重 0 13kg/尾。     

用于渔业资源调查评估的两种声学手段的比较

采用数字回声探测仪Bio Sonics DT-X(430 KHz)和双频识别声呐DIDSON(低频1.1 MHz、高频1.8MHz)对青草沙水库的渔业资源量、空间分布特征等进行了为期2 d的水声学调查。在调查过程中两种仪器同步工作,并采用放网捕捞的方法对青草沙水库中的鱼类样本进行采集,并测量其体重与体长。利用Echoview软件对两种仪器采集所得的声学数据进行分析处理。DIDSON的调查结果显示:水库鱼类总数约为936万尾,总的资源量约为705万kg,鱼类主要分布于水库的东部、中部地区。Bio Sonics DT-X的调查结果显示:水库鱼类总数约为1 079万尾,总的资源量约为604.24万kg,鱼类主要分布于水库的东北部地区。     

基于声学摄像仪的溯河洄游幼香鱼计数

至今主要靠目视计数来掌握香鱼(Plecoglossus altivelis)的资源量,这种方法很耗劳动力且精度低.由华盛顿大学研发的声学摄像仪DIDSON(Dual-frequency IDentification SONar)可在浑浊不清的水中摄取接近光学视频画质的图像.其附带软件虽可对体长为几十厘米的大个体鱼计数,但对于体长6 cm以下的小个体鱼,由于其回波信号弱,计数显得非常困难.本文提供了一种基于DIDSON的溯河洄游幼香鱼计数的新方法.首先从声学图像中消除静止的背景,提取出运动目标并除去噪音像素,然后用卡尔曼滤波器对剩下的目标进行跟踪,根据目标移动的特性把目标分为香鱼和垃圾2大类,在除去向下游移动的垃圾之后,可正确地计算向上游移动香鱼的数量.通过现场实测验证了上述声学计数方法的实用性和高效性.     

基于成像声呐的鱼类三维空间分布

针对海洋牧场中鱼群的三维空间分布问题,本研究提出一种利用成像声呐进行位置计算的方法。将成像声呐固定在船舷外侧的水下,并保证波束发射方向和声呐移动方向一致,通过走航的方式采集水下鱼群信息。首先对采集的原始数据进行图像处理,包括图像构建、背景去除、目标提取等,然后利用基于交互式多模型联合概率数据关联算法对水下目标进行关联处理,得到同一个目标在声呐水平视场中不同帧图像中的对应关系,在此基础上根据连续两帧图像中目标位置关系计算目标的空间坐标,最后结合关联算法获得多目标在三维空间中的运动轨迹以及深度分布情况。研究表明,本方法可以有效获取鱼群在水下的三维运动轨迹及其分布情况,这将为鱼类行为分析以及海洋牧场的资源评估提供技术支持。     

Comparison of the growth performance of offspring from cultured versus wild populations of arctic charr,Salvelinus alpinus (L.), kept at three different temperatures

The effects of three different temperatures on the growth and maturation of the offspring of cultured versus wild populations of juvenile arctic charr (Salvelinus alpinus L.) were investigated. The fish (start weight 17 g) were reared for 5 months at constant temperatures of 12, 14 and 16°C under a continuous light regime (LD24:0). Growth performance was significantly influenced by both temperature and source population. The offspring from the farmed fish displayed significantly higher mean weights at all temperatures compared with the offspring from the wild fish. The results indicate that the optimal temperature for growth (T_opt) decreases with increasing fish size in the offspring of both cultivated and wild fish. Significant differences in length–weight relationship were found, with the offspring of wild fish displaying higher condition factor throughout the experiment. The results demonstrate that the offspring from multiple generation farmed population of arctic charr are better adapted to high temperatures compared with the offspring (F₁ generation) from a wild population of arctic charr, and the former are also able to maintain growth at higher temperatures. There was a significant difference in maturation between the two populations, as the offspring from cultured fish displayed significantly lower level of maturation: 0%, 4% and 2% mature compared with 24%, 40% and 42% in the offspring from wild fish at temperatures of 12, 14 and 16°C respectively. The offspring from farmed strains of arctic charr thus appear to be the most suitable population for aquaculture.     

养殖和野生亚东鲑机体成分比较分析

亚东鲑(Salmo trutta fario)是鲑属鱼类在青藏高原仅有的鱼类种群,是亚东地区全国农产品地理标志产品。本研究对西藏亚东地区野生和养殖亚东鲑的常规营养成分及各组织氨基酸和脂肪酸组成进行分析,旨在比较野生和养殖亚东鲑营养成分的异同,为养殖亚东鲑的品质评价和饲料配方的完善提供参考信息。实验采集亚东河中野生亚东鲑和亚东渔业产业园中使用配合饲料养殖的亚东鲑各10尾用于相关成分分析,每尾为一个独立样本。结果显示,野生组肥满度显著低于养殖组,而全鱼水分和灰分显著高于养殖组。全鱼粗蛋白、粗脂肪以及肝脏常规成分在野生组和养殖组间无显著差异。野生组肌肉粗脂肪显著低于养殖组,而水分含量显著高于养殖组。野生组全鱼必需氨基酸总量显著高于养殖组,且野生组肌肉中苏氨酸、缬氨酸、苯丙氨酸、赖氨酸和甘氨酸含量显著高于养殖组。野生组全鱼、肌肉和肝脏中饱和脂肪酸、n-3多不饱和脂肪酸(n-3 PUFA)总量、EPA、C20:4n-6以及肌肉中DHA含量高于养殖组,而全鱼和组织中单不饱和脂肪酸和n-6 PUFA总量低于养殖组。综上所述,目前养殖亚东鲑和野生亚东鲑在机体成分上存在较大差异。由于养殖鱼类体成分很大程度上反映了饲料组成,因此,亚东鲑养殖中饲料营养组成可能有待进一步优化。     

Assessment of an automated fish counter in a Canadian river

Abstract. In order to assess the accuracy and reliability of automated fish counters for counting adult Atlantic salmon, Salmo salar L., a 'Logie' resistivity counter was installed in late June 1989 in the control dam above the fishway in Northeast River, Placentia, Newfoundland, Canada. The counter was in operation for 26 days (1–26 July). The accuracy of daily counts recorded by the counter was verified by visual counts of Atlantic salmon released from a trap located downstream of the counter and immediately above the fishway. All the fish released from the trap had to pass over the counter. A total of 517 salmon (mainly grilse) was released from the trap and the net number of upstream migrants recorded by the counter was also 517. This is the first test and use of an open-channel counter in eastern Canada. The results suggest that some counting fences and fishways may be easily adapted for installation of automated counters and that counters offer a cost-effective means of counting adult Atlantic salmon.     

The Image of Fish from Aquaculture Among Europeans: Impact of Exposure to Balanced Information

This study investigated the effect of balanced, nonpersuasive information related to safety, healthiness, and sustainability of aquaculture on the image of farmed fish among European consumers. It was demonstrated that there is neither positive nor negative influence of this type of information on the predominantly positive image of fish from aquaculture. Consumers who were exposed to information related to the EU origin and aquaculture related guarantee reported a more positive image of farmed fish. These results provide valuable input for transparent communication about fish farming practices which might increase consumer trust and will not harm the image of fish from aquaculture. Increasing consumers' knowledge about aquaculture and its positive effects on the image of farmed fish is also discussed as a pathway for maintaining and improving aquaculture's positive image in the future.     

Movements and spatiotemporal distribution of escaped farmed and local wild Atlantic cod (Gadus morhua L.)

Commercial farming of Atlantic cod (Gadus morhua L.) is now being developed in several countries. The ecological consequences of cod culture are poorly understood, but recent research suggests that Atlantic cod are more prone to escape from net pens than Atlantic salmon. Here, we describe the movements and the spatiotemporal distribution of farmed cod after escape relative to wild cod, both during and outside the natural spawning season. The experimental design included simulating escape incidents of farmed cod tagged with acoustic transmitters and using an array of automatic listening stations to monitor their dispersal and distribution. For comparison, local wild cod were monitored using the same array of receivers. The farmed cod dispersed rapidly after a simulated escape, they randomly distributed over large areas and their distribution overlapped with local wild cod. Moreover, escaped farmed fish were found at local cod spawning areas during the spawning season. The study also indicated that the recapture rate of escaped farmed cod was high compared with that of escaped farmed salmon. Thus, while our results showed that there is a considerable potential for ecosystem effects caused by escaped farmed cod, mitigating actions such as an efficient recapture fishery for escapees may be possible.     

Development of fish spatio-temporal identifying technology using SegNet in aquaculture net cages

In marine aquaculture, fish populations constantly decrease throughout the cultivation period because of mortality and escape. Current production management systems provide limited opportunities to count the cultured fish, making it difficult to estimate accurately the fish population in the cage. To overcome this problem, an automatic fish identifying method based on particle tracking velocimetry (PTV) flow visualization technology is proposed in this paper. The proposed method utilizes an image processing unit that extracts individual fish from the acquired image and a motion analysis unit that calculates the motion vector for each individual. Thus, the accuracy of the extraction results in the image processing unit affects the system’s counting results. To validate the efficiency and robustness of the image extraction performed by the image processing unit, individuals were extracted from images using the open-source image deep learning semantic segmentation method (SegNet), which is able to distinguish between the background and foreground in the images via analysis at the pixel level. SegNet is able to improve the image discrimination performance by multiplying the learning paths, and the robustness of the detection results can be ensured by changing the layer structure according to the detection target. Accordingly, the use of SegNet was evaluated in terms of the number of layers and images in the training set. The results of this study indicate that the application of SegNet with PTV technology represents a promising method for the automatic identifying and behavioral tracking of fish in an aquaculture net cage.     

The commercial exploitation of sea trout, Salmo trutta L.

Abstract. The net and coble catch of sea trout in the River North Esk was sampled between 1977 and 1979. A comparison of the length frequency distribution of these samples with those of sea trout taken in a trap which was assumed to be unselective revealed that the net and coble fishery was very selective. Only isolated fish below 35·0 cm were encountered in the commercial catch samples, yet between 25% and 41% of the upstream migratory sea trout taken in the trap during the netting season were below this length. The sea trout in the commercial catch samples were predominantly maiden, one-sea-winter fish. The dominant age class each year was the 2·1 + group, 3·1 + fish comprising the other major age class. The freshwater age of the maiden sea trout sampled declined as the season progressed. The proportion of previously spawned fish in the samples ranged between years from 12% to 15%. The mean length and mean weight of sea trout sampled from each year's catch showed little variation, ranging from 42·9 cm to 43·3 cm and 971 g to 972 g, respectively. The ratio of males to females in the 1979 sample was 1·00:2·18. The use of morphometric characteristics, including head length, pectoral fin length and adipose fin length was investigated with the aim of distinguishing the sex of fish taken early in the season from external features alone. Although in each month the mean head length as a percentage of fork length of males was greater than that of females, this difference was not sufficient to enable the rapid determination of sex during commercial catch sampling routines. The exploitation rate of sea trout reaching the most upstream major fishing station, Morphie Dyke, was estimated from the recapture of upstream adult sea trout removed from a trap and released in the main river 2 km downstream of Morphie Dyke. The percentage exploitation rate at this fishing station was found to range between 6·4% and 12·2%, and the percentage exploitation rate for the entire net and coble fishery was at a level of approximately 30% during the period of the study. The sea trout statistics of the North Esk net and coble fishery for the period 1925–1979 were examined, and the effect of a change in fishing effort on these figures is described. Recent catch figures, although below those reported during the mid-1960s, are above the level of catches reported prior to 1952.     

Vaccination and triploidy increase relative heart weight in farmed Atlantic salmon,Salmo salar L.

Heart morphology is particularly plastic in teleosts and differs between farmed and wild Atlantic salmon. However, little is known about how different culture practices and sex affect heart morphology. This study investigated how vaccination, triploidy and sex affected heart size and heart morphology (ventricle shape, angle of the bulbus arteriosus) in farmed Atlantic salmon for 18 months following vaccination (from c. 50–3000 g body weight). In addition, hearts were examined histologically after 7 months in sea water. All fish sampled were sexually immature. Vaccinated fish had significantly heavier hearts relative to body weight and a more triangular ventricle than unvaccinated fish, suggesting a greater cardiac workload. Irrespective of time, triploids had significantly heavier hearts relative to body weight, a more acute angle of the bulbus arteriosus and less fat deposition in the epicardium than diploids. The ventricle was also more triangular in triploids than diploids at seawater transfer. Sex had transient effects on the angle of the bulbus arteriosus, but no effect on relative heart weight or ventricle shape. From a morphological perspective, the results indicate that vaccination and triploidy increase cardiac workload in farmed Atlantic salmon.     

Comparison of stocking time and density on Gulf Killifish growth in freshwater ponds

The Gulf Killifish (Fundulus grandis) is a popular baitfish and a candidate for commercial‐scale production. For inland production, ponds may need to be stocked at different times and densities to meet market demands. Therefore, in Experiment 1, juveniles were stocked into freshwater ponds at a density of 25,000 fish/ha, with two cohorts (mean total length (TL) = 3.92; 3.52 cm) stocked 1 month apart and evaluated for 12 weeks. Cohort 1 had a lower overall survival (40%) than cohort 2 (79%); with no difference between mean final TL (8.46; 8.00 cm); reaching a market size of 6 cm in 22 days and 32 days respectively. In Experiment 2, juveniles (mean TL = 3.16; 3.23 cm) were stocked into freshwater ponds at two densities (25,000 fish/ha and 50,000 fish/ha). Mean final TL was greater in the lower stocking density (8.68 cm) than the higher stocking density (8.20 cm); with no differences in survival between treatments (75; 72%) respectively. Lower stocking and higher stocking densities reached a market size of 6 cm in 29 and 31 days respectively. These results suggest that multiple cohorts can be stocked and grown to market size in one season at a stocking density of 50,000 fish/ha.     

The prevalence of vertebral deformities is increased with higher egg incubation temperatures and triploidy in Atlantic salmon Salmo salar L.

Suboptimal egg incubation temperature is a risk factor for the development of skeletal deformities in teleosts. Triplicate diploid and triploid Atlantic salmon, Salmo salar L., egg batches were incubated at 6, 8 and 10 °C up until first feeding, whereupon fish were reared on a natural temperature before examination for externally visible skeletal deformities (jaw and spine) and radiographed for vertebral deformities and morphology at the parr stage. Increasing incubation temperatures and triploidy increased the number of fish showing one or more deformed vertebrae. Triploids had significantly higher mean vertebrae cranio‐caudal length (L) and dorsal‐ventral height (H) ratio at 6 and 10 °C than diploids, but triploidy had no effect on mean vertebrae centra area. Triploids demonstrated an increase in lower jaw deformities with increased incubation temperature, whereas jaw deformities were rare in diploids. Fish incubated at 10 °C had a significantly lower mean vertebral number than fish incubated at 6 °C, and triploids had lower mean vertebral numbers than diploids. Diploid fish with 58 vertebrae had a significantly higher mean vertebral centra area than fish with 59 vertebrae, but vertebral number did not affect the mean vertebral L/H ratio. The results are discussed with respect to the welfare and production of farmed salmonids.