Diseases of north European wrasse (Labridae) and possible interactions with cohabited farmed salmon, Salmo salar L

There have been several reported studies of wrasse health but none of these has shown transmission of wrasse diseases when stocked with farmed Atlantic salmon. Most of the studies have focussed on bacterial and parasite issues, including treatment of bacterial diseases with antibiotics and vaccination of wrasse. Classical and atypical furunculosis have been reported in wrasse following stress, and wrasse have been susceptible to vibrio infection. Further study is required on the vaccination of wrasse for furunculosis with latent carrier status to maximize survival. There are studies on viral diseases such as infectious pancreatic necrosis, infectious salmon anaemia and pancreas disease and although these did not give any undue concern for salmon health, there is also scope for further study in this area. Resident parasite communities of wrasse are largely host-specific and do not appear to be a threat to salmon. Given that wrasse have not, to date, been a vector of disease in salmon, attention should be placed on maintaining best practice in cohabiting wrasse with salmon. Other issues that should be addressed are good welfare of wrasse in pens and identifying measures of this, the identification of losses of wrasse in pens, being alert to potential emerging diseases through health screening of mortalities and assessing the risks associated with carrying forward wrasse from one salmon production cycle to the next. Issues of exploitation by fishing on wild wrasse stocks and improved biosecurity may be addressed by the increased movement by the industry to the stocking of farmed wrasse.     

环介导等温扩增技术快速检测大西洋鲑的研究

为探究环等温扩增技术(LAMP)在鲑科鱼类物种鉴定方面的应用,以大西洋鲑为研究对象,针对其线粒体CR区段设计特异性的LAMP引物,并通过单因素试验和正交试验研究反应体系中d NTP Mix、Mg~(2+)、甜菜碱终浓度对LAMP扩增结果的影响。结果表明,大西洋鲑LAMP扩增的最优条件为:引物SS-CR-F3/SS-CR-B3各0.2 m M,SS-CR-FIP/SS-CR-BIP各1.6 m M,dNTP Mix 1.4 m M,Mg~(2+)6 m M,甜菜碱0.8M,Bst DNA聚合酶8 U,扩增温度为65℃,反应时间60 min。在此条件下LAMP扩增产物电泳检测特异性强、稳定性好,对大西洋鲑DNA的检出限达0.01 ng·μL~(-1),并可对混合样本进行检测。本研究结果为大西洋鲑快速物种鉴定提供了一种重要技术手段,该技术可应用于鲑科鱼类物种鉴别的日常检验检疫和市场监管工作中。     

放养规格对银化期大西洋鲑生长的影响及生理响应机理

内分泌系统在调节大西洋鲑(Salmo salar L.)的银化过程中,除了要尽快建立更高效的渗透调节机制外,鱼体自身的生理反应变化还要更好地适应降海后的生活。试验研究了平均体质量(30.25±2.12)g(SW1)、(24.27±1.59)g(SW2)和(18.05±2.46)g(SW3)大西洋鲑,1~42 d光照周期为12L:12D;43~84 d为全光照下(24L:0D)的生长及生理响应机理。试验结果表明,SW2组大西洋鲑的肥满度、日增质量、饲料转化率、净增质量最高,与其他组差异显著(P0.05)。SW2组体质量、体长特定生长率均显著高于其他处理组(P0.05),各组间体质量、体长变异系数差异显著(P0.05)。试验前6周不同处理组大西洋鲑体长变异系数差异不显著(P0.05)。后6周全光照时,SW1、SW2组体长变异系数显著增加,且SW1组显著高于其他组(P0.05)。SW3组的大西洋鲑体质量变异系数变化较大。前6周光照期为12L:12D时,SW1、SW2两组体质量变异系数差异不显著(P0.05),后6周改为全光照时,3个处理组间体质量变异系数差异减小。但在84 d时,SW3组体质量变异系数显著高于其他组(P0.05)。随着养殖规格的增大,血红蛋白浓度升高,红细胞数目增加,说明鱼体需氧量增加。SW3组白细胞数目、淋巴细胞数目和中性粒细胞数目最高,表明鱼体抗病能力强。红细胞数目在SW1和SW2组间无显著差异(P0.05),但均显著高于SW3组(P0.05)。血栓细胞数目随着放养规格的增加而下降,且在3个规格组之间差异显著(P0.05)。中性粒细胞数目在3个规格组之间并没有显著性差异(P0.05)。SW2组总蛋白、白蛋白含量最高,且各组间差异显著(P0.05)。总胆固醇、甘油三酯浓度随鱼体规格增大而增加(P0.05),表明大西洋鲑血液和体内对能量的利用增强。SW2组代谢产物尿酸、尿素浓度最高,且SW1、SW2组的浓度值均显著高于SW3组(P0.05)。SW3组大西洋鲑血清中总胆红素显著高于其他两组(P0.05)。各组间大西洋鲑血清中葡萄糖浓度没有显著性差异(P0.05)。SW3组肌酸激酶浓度最高,但各组间没有显著性差异(P0.05)。该研究结果建议选择体质量(24.27±1.59)g的大西洋鲑开始银化,利于优化养殖条件、以较低成本增加单位水体养殖产量和苗种规模化生产。     

Individual variation in early life-history traits in brown trout

Abstract – We studied the variability of early life history traits in individually raised progeny of brown trout Salmo trutta L. Eggs from two dams were each fertilized with sperm from 10 sires, producing 20 full-sib families. Each individual progeny was followed from fertilization until death without exogenous food. Egg size was positively correlated with a number of life-history traits, especially length and yolk sac volume at hatching and length at death, and these traits were strongly influenced by maternal effects. We found significant additive genetic variance for growth rate, length at death and life span without external food. Thus these early life-history traits may be modulated by natural selection. We found positive phenotypic and genetic correlations between most early life-history traits. However, life span without external food was negatively correlated with growth rate, indicating a genetic trade-off. ^Note     

Incidence of hybridization between Atlantic salmon, Salmo salar L., and brown trout, Salmo trutta L., in Ireland

The substantial growth of the farmed salmon industry in Europe since the 1970s has highlighted concerns regarding the genetic impact of escaped farmed salmon on wild salmonid stocks. High incidences of salmon × trout hybrids have been recorded in rivers situated near intensive salmon farming in Norway and Scotland, which may be indicative of a breakdown in reproductive isolation between salmon, Salmo salar L., and brown trout, Salmo trutta L. In the present study, salmonid fry and 0+ parr were collected from rivers in western Ireland. Allozyme and minisatellite DNA analysis were carried out on fry to determine the frequency of F1 hybrids from 10 rivers located within 38 km of salmon farms and three rivers at least 80 km from salmon farms. A total of 49 hybrids were recorded from 4135 salmonid fry (frequency = 1.2%). Mitochondrial DNA analysis showed that all hybrids arose from Atlantic salmon female × brown trout male crosses. Hybrid parr were recorded from one of the low-risk rivers (1.0%), but were present in seven out of the 10 catchments located within 38 km of salmon farms, with frequencies ranging from 0.7% to 3.1%. The results of the present survey, which represents the first extensive record of the levels of salmon-trout hybridization in Ireland, are discussed in relation to the continued growth of salmon farming in this country.     

A system for automatic recording of fish tagged with coded acoustic transmitters

A telemetry system designed to automatically record the presence and swimming direction of fish tagged with coded acoustic transmitters is described. The present paper presents results from an extensive mapping of signal strengths and the proportion of correctly identified codes from a transmitter at various positions outside automatic listening stations (ALS). The system is evaluated on the basis of two field seasons, during which 107 Atlantic salmon, Salmo salar L., were tagged with acoustic transmitters in a fjord system in south-western Norway. By installing one ALS (two at high water discharges) in the mouth of the River Suldalslågen and two ALSs in the Hylsfjord, the presence and swimming direction of all tagged salmon entering the river and the inner part of the 750-m-wide Hylsfjord were recorded.     

Prespawning migratory behaviour and spawning success of sea-ranched Atlantic salmon, Salmo salar L., in the River Gudenaa, Denmark

The migratory behaviour of sea-ranched Atlantic salmon, Salmo salar L., was analysed by radio-telemetry in the River Gudenaa, Denmark. The main objectives were to: (1) estimate mortality of returning adults through the fjord; (2) observe rate of progression and migratory pattern in the fjord and river; and (3) record whether spawning occurs in the river. Forty-two returning salmon (19 males and 23 females of total body length from 60–97 cm) reared and released as smolts, were caught and equipped with external radio transmitters in the outer estuary of the River Gudenaa in 1994 and 1995. Of the tagged salmon, 18 (43%) were caught in the estuary, four (10%) were not recorded after release and 20 (47%) entered the river. The mean rate of progression through the fjord was 7.6 km d−1 (range 1.4–18.2) in 1994 and 5.4 km  d−1 (range 1.6–17.1) in 1995. Eleven salmon were alive at the onset of the spawning period. Eight were retrieved dead from the river during or after the spawning period; four with empty gonads assumed to be successful spawners, and four with intact gonads. In 1994, unsuccessful spawners (found dead with intact gonads) entered the river earlier and had a longer total migration distance in the river compared to successful spawners. This suggests that spawning success of sea-ranched salmon is associated with time of river entry and river migration length.     

Tissue and organ distribution of 14C‐activity in dextrin‐adapted Atlantic salmon after oral administration of radiolabelled 14C1‐glucose

Accumulation of ¹⁴C in various tissues and organs was studied in three different groups of 0.8‐kg Atlantic salmon Salmo salar force‐fed with ¹⁴C₁‐glucose in order to evaluate if metabolism of glucose depended on adaptation to dietary carbohydrate level. The salmon had been fed diets supplemented with 0, 100 and 200 g maize dextrin kg^?1 for 10 months before the experiment. The fish were force‐fed 6.65 × 10⁴ Bq of ¹⁴C₁ glucose kg^?1 BW, in gelatin capsules. Fish for analysis were obtained 16 h later. ¹⁴C was measured in blood plasma, gill, kidney, liver and white muscle, and in lipid extract of liver. The liver contained most ¹⁴C, followed by heart, blood plasma, gill and liver lipid extract, while kidney and muscle contained the least ¹⁴C per gram or millilitre tissue. The muscle contained most radioactivity, on an estimated total tissue basis, followed by liver, blood plasma, gill, liver lipid extract, kidney and heart tissue. Thirty‐eight per cent of the orally administered ¹⁴C was recovered in the salmon adapted to the diet without dextrin after 16 h. This was significantly (P < 0.05) higher than the 30% and 32% recovered in the salmon adapted to diets with 10% and 20% dextrin. This effect on adaptation to dietary dextrin level in glucose uptake or metabolism was supported by a trend (P < 0.10) toward higher radioactivity per gram or millilitre of each individual tissue in the fish adapted to the diet without dextrin, when compared with the other two adaptation regimes.     

Resistance of sea lice, Lepeophtheirus salmonis (Krøyer), to hydrogen peroxide on farmed Atlantic salmon, Salmo salar L.

Hydrogen peroxide has been the only medicine used to treat salmon infected with sea lice [Lepeophtheirus salmonis (Krøyer)] on many farms in Scotland since 1992 and reports have suggested reduced treatment efficacy. The present study tests the sensitivity of sea lice to exposure to hydrogen peroxide under farm conditions and also in vivo by comparing lice from a farm with suspected resistance and lice from a farm that had not been pre‐exposed to hydrogen peroxide. In bin treatments on fish from a farm treated with hydrogen peroxide on 41 occasions, numbers of ovigerous lice declined by only 15% and 16% in two replicates and other mobile stages by 25%. Where hydrogen peroxide had not been used, ovigerous females declined by 90% and 87% and other mobile lice stages by 97% and 99%. These trials and observed poor efficacy of cage treatments, for example only 7.5% reduction in lice numbers when fish were treated with 2000 p.p.m. for 20 mins, indicated resistance of lice to hydrogen peroxide. The mechanisms involved in the development of resistance, possible genetic selection for lice with reduced carapace permeability or detoxifying enzymes such as catalase, or tolerance through induction by subtherapeutic exposure are reviewed. Implications for lice control strategies relying on hydrogen peroxide are discussed.