Sea lice treatments, management practices and sea lice sampling methods on Atlantic salmon farms in the Bay of Fundy, New Brunswick, Canada

Proper monitoring of all stages of sea lice is imperative to ensure the strategic timing of treatments. Although sea lice receive close attention and management for production purposes, there are no regulations for the reporting of lice burdens on salmon farms in Atlantic Canada, nor are there officially standardized protocols for conducting sea lice counts in the field. The purpose of this study was to complete a survey of Atlantic salmon farms in the Bay of Fundy, NB, Canada. The survey addressed many aspects of sea lice monitoring and control, including methods for sea lice sampling at the site, types of treatments administered for control of sea lice and management practices and decisions regarding the control of sea lice. A total of 83 surveys were completed from July to December 2002. Twelve of the 60 respondents owned and/or operated more than one site and completed a survey for each of their sites at the time of the interview. The position of individuals surveyed included 48 site managers (representing 63 sites), three site owners (representing 11 sites), eight individuals who were both owner and manager (representing nine sites) and one site veterinarian (representing one site). Surveys were completed on 30 sites from the Limekiln Bay and surrounding areas, 23 sites from Grand Manan Island, 18 sites from Deer Island, six sites from Campobello Island and six sites from Passamaquoddy Bay. Fish farmers, in concert with their veterinarians, generally perform intensive monitoring and control practices. However, there is a continued reliance on emamectin benzoate (SLICE^®) for sea lice control on Atlantic salmon farms in the Bay of Fundy, which raises concerns regarding the potential for sea lice to develop resistance to the drug.     

Diel migration patterns of Atlantic salmon smolts with particular reference to the absence of crepuscular migration

Abstract –  The real-time diel pattern of Atlantic salmon smolt migration was observed for 8 years using automatic resistivity counters verified by video surveillance. A clear dominant nocturnal migration was demonstrated early in the migration period, later becoming increasingly diurnal, until rates became approximately equal at day and night. Migration patterns were related to water temperature, such that when mean daily temperatures were below 12 °C, hourly rates of migration were significantly lower during the day than at night. When daily mean temperatures exceeded 12 °C, there was no significant difference between diurnal and nocturnal migration rates. Migration patterns showed a distinct suppression of migration at dawn and dusk throughout the migration period. It is hypothesised that this behaviour is an active decision and/or an adaptive strategy either to take advantage of increased food in the form of invertebrate drift or to reduce predation risk from actively feeding piscivores or both.     

Effect of brown trout body size on post-stocking survival and pike predation

Abstract –  A total of 40 (20 age-3 + 20 age-4) radio-tagged hatchery-reared brown trout ( Salmo trutta L.) and 40 wild radio-tagged northern pike ( Esox lucius L.) were released into a regulated river. Age-3 brown trout were predicted and observed to be highly vulnerable to predation by pike (50% mortality), whereas age-4 brown trout were predicted and observed to enjoy an almost absolute size refuge from predation (5% mortality). Almost half of the fish from both age groups similarly emigrated and survived from the river within 3 days of the release. However, there was a considerable difference in survival between age groups for fish that remained in the river for a longer period. Of these, all except one age-3 brown trout were eaten by pike, whereas all but one age-4 fish survived predation.     

不同水温下虹鳟血液红细胞数及血清中血糖与矿质元素含量测定

采用显微记数法和使用日立7170A全自动生化分析仪与贝克曼CX-3电解质分析仪,测定水温14℃、19℃、23℃时虹鳟(Salmoirideus Gibbons)血液中红细胞数量和血清中血糖与矿质元素含量。结果表明:水温从14℃升至23℃,虹鳟血液红细胞数量显著减少;血清中血糖含量在水温19℃时表现为增加、在23℃时又表现为减少;铜元素含量在水温23℃时较14℃时增加84.06%,钾、磷、钙、镁、钠、氯、铁元素含量在水温23℃时较14℃时增幅为1.65%～33.66%。     

Distribution of lipid droplets is an indicator for egg quality in brown trout, Salmo trutta fario

In the eggs of the brown trout, Salmo trutta fario, lipid droplets are clearly visible beneath the oolemma on the surface of the protein yolk. When examining the distribution of lipid vesicles in egg batches of different quality, four categories of lipid vesicle distribution could be distinguished: In the first category, the lipid droplets were evenly distributed throughout the egg. These egg batches had a high quality (percentage of eggs developing to eyed stage embryos: 96.2 ± 5.2). Some lipid droplets had the tendency to coalesce in one pole of the egg in the second category. This coalescing of lipid droplets was accompanied with a reduction in egg quality to about 50% of the first category (% of eyed stage embryos: 40.6 ± 15.2). In the last two categories, the lipid droplets were mostly coalesced in one or two poles of the egg and the egg quality was very low (% of eyed stage embryos: 3.3 ± 2.9 and zero, respectively). In conclusion, examination of lipid droplets distribution, in brown trout, can distinguish between high and low quality eggs in an easy and reliable way.     

Plasma levels of vitamin D3 metabolites during parr-smolt transformation of Atlantic salmon Salmo salar L.

Plasma vitamin D and vitamin D metabolites were measured in Atlantic salmon parr during smoltification and after transfer to seawater. The fish were fed commercial feed for 5 months under natural light, and Na⁺/K⁺ ATPase was measured as an indicator of the smoltification status. No significant differences were recorded in the level of plasma vitamin D metabolites. However, a tendency of increasing plasma concentration of 25OHD₃ and also a temporary increase in plasma 1,25(OH)₂D₃ and 24,25(OH)₂D₃ were recorded prior to seawater transfer. The minor changes in plasma levels of the metabolites indicate a role of the vitamin D metabolites during parr–smolt transformation, although we do not know whether the increased levels are caused by increased synthesis of the metabolites or by decreased binding to receptors or decreased excretion.     

促性腺激素诱发大西洋鲑卵黄发生期卵巢滤泡释放性类固醇激素的离体研究

提要应用大麻哈鱼(Oncovhynchus keta)促性腺激素(GTH)诱发大西洋鲑(Salmosalar)卵黄发生期的离体卵巢滤泡(直径为3．4毫米)产生性类固醇激素的研究表明，不论用0．1或1微克／毫升GTH刺激，经培育10天后，未出现卵母细胞卵核消失的现象，卵核偏位也不明显。对培养液中17α，20β-双羟孕酮(17α20βP)的积累浓度测定结果，仅1微克／毫升GTH组含少量的17α20βP；0．1微克／毫升GTH组，培养液中雌二醇的积累浓度明显高于对照组和1微克／毫升GTH组，并为后者的两倍。除雌二醇外，孕酮，17α-羟孕酮，17α20βP，雄烯二酮和睾酮的产生，都呈现对GTH剂量的依赖关系，1微克／毫升GTH组的产生量明显高于0．1微克／毫升GTH组和对照组。离体研究的结果表明，处于卵黄发生期的卵巢滤泡对低剂量(0．1微克／毫升)和高剂量(1微克／毫升)GTH的反应不同。低浓度的GTH，引起性类固醇激素生物合成的途径沿着形成雌二醇的方向进行，雄激素被芳香化成雌激素，雌二醇再而刺激肝脏合成卵黄物质的前体，从而促进卵黄发生。高浓度的GTH，有抑制雌二醇合成的作用，而是促使卵母细胞向着最终成熟的方向发展，使性类固醇生物合成的途径转向形成大量雄激素和孕激素，特别是17α20βP。这与已充分生长和卵黄积累完成的卵巢滤泡离体试验的结果一致，与活体观察以上各种性类固醇激素的变化一致。     

Presence of anti-Neoparamoeba sp. antibodies in Tasmanian cultured Atlantic salmon, Salmo salar L

Previous studies have indicated that when Atlantic salmon, Salmo salar L., are exposed to Neoparamoeba sp. the fish produce anti-Neoparamoeba sp. antibodies. It appears unlikely that these antibodies elicit any specific protection against amoebic gill disease (AGD) as fish with demonstrable activities have been affected by AGD. Experiments were conducted on Atlantic salmon cultured throughout Tasmania to assess the natural production of antibodies towards Neoparamoeba sp. Fish were sampled from areas where AGD was prevalent and from areas where there had been no reported cases. An enzyme-linked immunosorbent assay (ELISA) was used to measure anti-Neoparamoeba sp. antibody activities in serum. All fish from sea water had antibody activities greater than the negative control fish, including fish from areas with no reported cases of AGD. Time trial samples indicated that time after transfer to sea water did not appear to be a significant (P > 0.05) factor in antibody activity, however location was (P < 0.05). There was no agreement (corrected kappa value, 0.16) between the ELISA result and the isolation of Neoparamoeba sp. from the gills of the same fish. The results suggest that Atlantic salmon in seawater culture in Tasmania produce anti-Neoparamoeba sp. antibodies regardless of infection history, suggesting the presence of Neoparamoeba sp. in the environment.