Cardiac pathology associated with the infection of Oncorhynchus mykiss Walbaum with Apatemon gracilis Rud. 1819

The chronological development of gross pathological and histopathological changes associated with the infection of rainbow trout, Oncorhynchus mykiss Walbaum, with metacercariae of Apatemon gracilis Rudolphi was investigated.     

Arteriosclerosis in steelhead trout, Oncorhynchus mykiss (Walbaum): a developmental analysis

Arteriosclerosis in Oncorhynchur mykiss has been examined histologically in parr, smolts, spawning adults and post-spawning adults captured during downstream migration. All stages of fish from the Clearwater River in Idaho are characterized by the presence of lesions in the main vessel on the bulbus arteriosus. The incidence is lowest in parr, increases significantly in smolts, and is present in 100% of spawning fish. Regression of lesions was not observed in either hatchery or wild fish after spawning.     

Experimental studies on the effect of Gyrodactylus colemanensis and G. salmonis (Monogenea) on density of mucous cells in the epidermis of fry of Oncorhynchus mykiss

Fry of Oncorliynclius mykiss were experimentally infected with the ectoparasites Gyroducrylus rolenirmensis and Gyroducrylus salnionis (Monogenea) and changes in mucous cell density in the epidermis covering the caudal fin were monitored during an ensuing 42 day epidemic. At 10° C, infections of G. colemanensis rose to a recorded peak of 90 to 1 15 worms on day 27 post-infection and then declined toward extinction. Intensity of G. salmonis remained low throughout the experiment. Infection produced no clinical signs of disease and did not influence fry growth or survival. However, infected fish did have a 50% reduction in the number of mucous cells in the epidermis of the fin. The changes were first detected on day 24 post-infection and became increasingly pronounced during the subsequent 1 day period when parasite numbers declined drastically. The study hypothesizes that parasite activity on the surface indirectly leads to reduction in mucous cells through disruption of cell dynamics within the epidermis.     

Is there an optimal haematocrit for rainbow trout,Oncorhynchm mykiss (Walbaum)? An interpretation of recent data based on blood viscosity measurements

The viscosity of blood from rainbow trout was measured following manipulation of haematocrit by bleeding, hypoxia. exercise, and anaesthesia. Blood viscosity when measured at high shear rate (225 s ¹) was proportional to haematocrit, but the dependence of viscosity on shear rate was far less for swollen erythrocytes from exercised and anaesthetized trout. Erythrocyte swelling was most marked in exercised and anaesthetized trout, and is a confounding factor when considering the effect of haematocrit on viscosity.
The viscosity of blood with variable haematocrit, but constant mean cell Hb concentration, indicated that the relative oxygen transport capacity in trout was optimal at a haematocrit of 30%. Data from this, and earlier studies show that haematocrit in trout is variable and labile, yet none of the haematocrit values following manipulations are less than 85% of optimal. Optimal haematocrit is however, significantly higher than measured values from either cannulated or acutely venesected resting trout.     

Lysozyme activity in rainbow trout, Oncorhynchus mykiss (Walbaum), stressed by handling, transport and water pollution

Blood lysozyme activity was determined in rainbow trout that were stressed by handling and transport, or suffered from acute ammonia poisoning. To optimize the lysoplate assay, the pH dependence of the lysozyme activity was studied. For serum and kidney lysozyme, the pH optimum was 5.5 to 6.0. Ventilation frequency and plasma glucoseconcentration of the fish were used as stress indicators. Less severely stressful situations, such as 30 min of handling, brought about either a stimulation or a suppression of the lysozyme activity. Strong stressors, such as transport lasting 2 h or acute water pollution, reduced the lysozyme level significantly. The decrease of lysozyme activity due to handling and transport persisted for 24 h, but the activity returned to normal within 2 weeks following confrontation with the stressor.     

Acoustic measurement of trout distributions in Spada Lake, Washington, using stationary transducers

Diel patterns in the spatial distribution of rainbow and cutthroat trout were studied with stationary acoustic transducers, gillnets, and setlines in Spada Lake during summer thermal stratification. Four diel periods (dawn, 03.00–07.00 hours; day, 07.00–19.00 hours; dusk, 19.00–23.00 hours; night, 23.00–03.00 hours) and two horizontal strata (nearshore, bottom depth < 8 m; offshore, bottom depth > 8 m) were identified from fish distribution patterns. During the day, trout were almost exclusively offshore and their densities were highest at intermediate depths of the water column (4–16 m). From dusk to dawn, trout were in intermediate and shallow depths (0–4 m) of the offshore and nearshore strata. The mean depth of capture was significantly deeper for cutthroat trout (9 m) than for rainbow trout (3m). Both species primarily inhabited the epilimnion and metalimnion where temperature ranged from 22.5 to 11.0°C and were nearly absent from deeper, cooler waters. Dissolved oxygen levels ranging from 3.9 to 8.6 mg/l did not seem to influence trout distributions.     

Experimental differences in mortality patterns between European minnows, Phoxinus phoxinus, infected with sympatric or allopatric trematodes, Diplostomum phoxini

A factorial experiment was conducted to examine if the digenetic trematode parasite Diplostomum phoxini influences minnow growth and survival negatively and if different parasite populations differ in their effects on hosts. Juvenile full-sibling minnows from a lake located at the northern edge of the Swiss Alps were infected experimentally with D. phoxini from either their own or another lake. When exposed to sympatric parasites, the minnows survived a low and a high infection dose more or less equally, but with allopatric parasites mortality increased with infection dose. Parasites did not reduce host growth and minnows exposed to a low infection dose grew quicker than either non-infected ones or ones exposed to a high infection dose. Thus, the results show different patterns of pathogenicity between two parasite populations and suggest that (1) the observed differences are at least partially genetic and that (2) the co-evolved, sympatric host-parasite association has reached a degree of low pathogenicity. Differences between the findings presented here and those of a previously published study are discussed.     

The host specificity of Gyrodactylus salaris Malmberg (Platyhelminthes, Monogenea): susceptibility of Oncovhynchus mykiss (Walbaum) under experimental conditions

An experimental epidemiological approach was chosen to study the survival and infection dynamics of Gyrodactylus salaris on juvenile rainbow trout, Oncorhynchus mykiss , in the laboratory. A marked heterogeneity in the host stock was apparent. The rainbow trout could be divided into three groups on the basis of parasite survival and infection pattern on individually isolated fish: (1) hosts receptive to initial parasite attachment, but unreceptive to parasite establishment and reproduction; (2) hosts moderately susceptible to parasite establishment and reproduction, but which, after a period of restricted parasite population growth, responded, recovered and eliminated the parasites; and (3) hosts very susceptible to parasite infection and reproduction, but which, after a period of significant parasite population growth, responded, recovered and eliminated the parasites. These different patterns are considered to reflect genetic differences between host individuals. Parasite aggregation was also shown to be an important factor in the outcome of the host-parasite association. The parasites were finally eliminated on the individually isolated hosts, but not on hosts maintained in batches and so host population size and immigration of fresh. previously unexposed, hosts appeared to be important for growth and maintenance of the parasite population. The parasite was not found to cause host mortality. Rainbow trout was a suitable host for G. salaris , capable of transmitting the parasite to new localities as a consequence of stocking programmes or migratory behaviour.     

Uptake of vitellogenin into oocytes during early vitellogenic development in the rainbow trout, Oncorhynchus mykiss (Walbaum)

Uptake of ³H-vitellogenin (³H-VTG) into oocytes of various sizes was investigated during early vitellogenic development in the rainbow trout, Oncorhynchus mykiss (Walbaum). Females were injected with ³H-VTG and uptake into oocytes of different sizes (<0.4,0.4–0.59, 0.6–0.79, 0.8–0.99 and 1.0 1.2 mm in diameter) measured. Oocytes measuring less than 0.6 mm in diameter appeared unable to sequester VTG and were therefore considered pre-vitellogenic. Oocytes measuring 0.6 mm or more all sequestered VTG. The larger the oocyte, the more ³H-VTG it sequestered, even when uptake was expressed per unit surface area. The latter observation could be due to an increase in the number of VTG receptors per unit surface area, an increase in the rate of turnover of the VTG receptor, greater access of VTG to the receptors as oocytes grow, or a combination of any of these factors. The data suggest that the ability to sequester VTG is developmentally regulated.     

Six diagnostic single nucleotide polymorphism markers for detecting introgression between cutthroat and rainbow trouts

Ten primer pairs were screened to develop single nucleotide polymorphism (SNP) TaqMan assays that will distinguish California golden trout and some rainbow trouts (Oncorhynchus mykiss sspp., O. m. aguabonita) from the Paiute and Lahontan cutthroat trouts (Oncorhynchus clarkii seleniris, O. c. henshawi). From these 10 primer pairs, one mitochondrial and five nuclear fixed SNP differences were discovered and developed into TaqMan assays. These six assays will be useful for characterizing and monitoring hybridization between these groups. Additional Oncorhynchus clarkii sspp. and Oncorhynchus mykiss sspp. were assayed to determine if these assays are useful in closely related species.     

虹鳟补体活化调节因子CD46的分子特征及功能

为进一步研究硬骨鱼类中补体活化调节因子的分子特征和功能, 研究克隆了虹鳟(Oncorhynchus mykiss)的CD46基因, 对其分子特征进行了系统分析, 结果显示: 虹鳟CD46基因由10个外显子和9个内含子组成, cDNA序列全长2812 bp, 编码317个氨基酸, 蛋白序列由1个信号肽、4个SCR结构域、1个跨膜区和1个胞内区组成, 预测分子量为33.9 kD。基因组共线性分析显示, 虹鳟CD46基因位于16号染色体, 其基因座在脊椎动物中具有保守的共线性。组织和白细胞亚群表达分析显示, 虹鳟CD46基因在各种组织和白细胞亚群中均有表达。为了进一步阐明虹鳟CD46的免疫功能, 研究原核表达纯化了标签蛋白GST和融合蛋白GST-CD46。溶血活性实验表明, 与GST相比, GST-CD46能够显著抑制虹鳟血清对兔红细胞的溶血活性, 且呈现剂量依赖效应, 表明虹鳟CD46是补体活化的调节因子。此外, 研究用HEK293T细胞过表达了GFP和GFP-CD46。细胞损伤实验显示, 与GFP相比, GFP-CD46能够显著抑制虹鳟血清对HEK293T细胞的损伤, 进一步表明虹鳟CD46是补体活化的调节因子, 能够保护细胞免受补体系统的损伤。总之, 研究不仅增加了对虹鳟CD46的分子特征和功能的认知, 还为深入研究此分子的免疫功能及其在抗病免疫中的应用提供了理论基础。     

基于UPLC-Q-TOF/MS代谢组学探究虹鳟鳃对热应激的生理反应

全球气温日趋升高导致的水温上升可引起虹鳟(Oncorhynchus mykiss)代谢紊乱, 为解析其在热应激下的代谢变化特征, 研究基于UPLC-Q-TOF/MS代谢组学技术, 探究了虹鳟鳃靶器官在高温暴露(20℃和24℃)及恢复到初始温度(14℃)下的代谢生理反应。研究结果表明, 与对照组相比, 在20℃、24℃高温组和14℃恢复组中分别鉴定出128、130和108种差异显著代谢物。在高温暴露下, 亚油酸、花生四烯酸等与脂质代谢相关的代谢物及还原型辅酶Ⅱ(NADPH)、谷胱甘肽(GSH)、谷胱甘肽二硫化物(GSSG)等与细胞氧化还原状态相关的代谢物均发生显著改变。富集分析表明这些代谢物主要涉及虹鳟鳃的甘油磷脂代谢、鞘脂代谢、亚油酸代谢、花生四烯酸代谢、磷酸戊糖途径和谷胱甘肽代谢等代谢通路, 但在温度恢复到14℃后, 除鞘脂代谢外, 其他代谢途径均未恢复至正常状态。上述结果表明, 热激导致了虹鳟鳃靶器官的脂质代谢紊乱, 可能导致鳃细胞膜的结构和功能的损伤, 诱使鳃细胞出现炎症反应, 并产生免疫应答。同时, 虹鳟鳃细胞通过磷酸戊糖途径产生的NADPH来调节谷胱甘肽代谢中GSH/GSSG比值以提高细胞的抗氧化能力来对抗氧化应激, 防止细胞凋亡。研究结果为理解热应激下虹鳟的生理反应提供了科学依据。