Changes in plasma prolactin and growth hormone concentrations during freshwater adaptation of juvenile chum salmon (Oncorhynchus keta) reared in seawater for a prolonged period

Freshwater adaptability of chum salmon was examined in juvenile fish reared in seawater for 4 months. The fish, weighing about 40g, were transferred directly to fresh water in October, when their cohorts are migrating in the North Pacific Ocean. Plasma sodium concentration decreased from 167 mM in seawater to about 130 mM during the first 24h, and increased gradually during 2–7 days after the transfer. No immunoreactive prolactin (PRL) was detected in the plasma of the seawater-adapted fish nor during the first 24h in fresh water. Significant levels of PRL were detected after 2–3 days. The maximal level (2.6 ng/ml) was observed after 5 days and became undetectable again after 7 days; no significant correlation was seen between the changes in plasma sodium and PRL levels during the transfer. Plasma growth hormone levels were relatively constant, except for a significant decrease 12h after the transfer. Although plasma thyroxine levels were highly variable during the experiment, a significant decrease and an increase were observed 12h and 5 days after the transfer, respectively. The present study indicates that juvenile chum salmon retain hyperosmoregulatory ability even after prolonged rearing in seawater. Examination of turnover rates, rather than changes in plasma levels, seems to be essential to clarify the osmoregulatory roles of the hormones.     

Protein degradation and protease activity of chum salmon (Oncorhynchus keta) muscle during spawning migration

Sarcoplasmic protein content decreased significantly and myosin heavy chain was degraded gradually during spawning migration of chum salmon (Oncorhynchus keta). Acid and neutral proteinase activities increased significantly during spawning migration. These proteinase activities were higher in females than in males. High levels of acid proteinase were not caused by the injury of lysosomal membranes. Considering the physiological states of chum salmon, neutral proteinase activity might be related to the degradation of muscle protein. As the changes in serum sex steroids were similar to those in the protease activities during spawning migration, it was considered that high levels of protease activity during spawning migration were closely related to the serum levels of androgens.     

Nonrandom distribution of chum salmon stocks in the Bering Sea and the North Pacific Ocean estimated using mitochondrial DNA microarray

More than 1,000 age-identified chum salmon Oncorhynchus keta collected at 23 stations in the Bering Sea and the North Pacific Ocean in June to July 2003 were used to estimate their origin of stocks using a DNA microarray developed for analyzing the mitochondrial (mt)DNA haplotypes. The observed haplotype distribution was nearly the same as that reported previously for fish collected in September 2002 and 2003 in the present surveyed areas. A conditional maximum-likelihood method for estimation of stock compositions indicated that the Japanese stocks mainly distributed in north central Bering Sea, whereas the Russian stocks were mainly in western Bering Sea. The North American stocks were abundant in eastern Bering Sea and around the Aleutian Islands. Such an area-specific stock composition was not significantly different between mature and immature fish. Thus, the combined results of 2 years suggest that the distribution of chum salmon is nonrandom in the surveyed areas in summer and autumn, and that fish of the same origin migrate together to the same area irrespective of age.     

Changes in plasma somatolactin levels during spawning migration of chum salmon (Oncorhynchus keta)

Plasma somatolactin (SL) concentrations were examined in chum salmon in relation to gonadal maturation; immature salmon in the Bering Sea at various stages of maturation, and mature salmon during upstream migration caught at the ocean, bay and river. Plasma SL concentrations as well as plasma prolactin (PRL) and growth hormone (GH) levels in the immature fish caught in the Bering Sea were maintained essentially at similar levels. Plasma SL in mature salmon increased significantly from the fish in the ocean to the fish in the river in both sexes. Although all the fish had fully developed gonads, females completed ovulation while still in the bay, whereas final spermeation in males was achieved after entry into the river. Thus, no clear correlation was seen between plasma SL levels and final gonadal maturation. On the other hand, plasma PRL concentrations in both male and female fish were higher in the fish in the river than those in the ocean and bay, and plasma GH levels were higher in both sexes in the fish in the bay and river than those in the ocean. Plasma levels of triglycerides, glucose, free fatty acids and ionized sodium and calcium were also examined. Significant-negative correlations were seen between plasma SL and plasma ionized calcium in mature male salmon, and between plasma SL and plasma triglycerides in mature female salmon. Although our findings do not rule out the possibility of the involvement of SL in final maturation, the results indicate that SL seems to be involved at least in energy and/or calcium metabolism during the spawning migration.     

大麻哈鱼胚胎耳石的茜素红标记及其效果评价

以人工繁育大麻哈鱼(Oncorhynchus keta)发眼后胚胎为研究对象, 设置4个茜素红染料质量浓度梯度(10 mg/L, 20 mg/L, 40 mg/L, 80 mg/L)和4个浸染时间梯度(8 h, 16 h, 24 h, 32 h), 分析茜素红染料在耳石上的沉积情况, 以及不同暂养天数的动态变化, 以期为大麻哈鱼标志放流技术及效果评估提供基础参考。结果表明, 茜素红在矢耳石和微耳石上都能形成良好标记, 在可见光和黄绿激光下均检测到标记带。随着暂养时间的延长, 可见光下标记逐渐减弱, 至80 d基本消失, 而在黄绿激光下标记区能长久保持, 荧光强度无减弱迹象。对不同时间点的标记级数随浓度变化关系进行曲线拟合, 结合安全评估, 得出适宜胚胎期大麻哈鱼耳石群体标记的条件为: 浸染质量浓度(w/v)为25.9~40 mg/L, 浸染时间为15.6~24 h, 并且在二次函数y=0.055x²–3.861x+86.9(x表示时间值, y表示浓度值)之下的曲边三角形区域选择浓度和时间点。标记后不同采样时间点的新生轮纹数与暂养天数线性相关性显著, 矢耳石和微耳石相关方程的斜率分别为0.965和0.924, 表明大麻哈鱼胚胎-仔稚鱼后期矢耳石与微耳石上的沉积轮为日轮。     

Immunoreactive somatolactin cells in the pituitary of young,migrating, spawning and spent chinook salmon,Oncorhynchus tshawytscha

Immunocytochemical techniques using an antiserum to cod somatolactin (SL) demonstrated the presence of SL cells in the intermediate lobe of the pituitary in Oncorhynchus tshawytscha. The cells were small in yearling fish. Two groups of maturing fish were studied. In the spring run salmon collected in April and May during the upstream migration, the SL cells appeared stimulated. In September, during spawning, SL cell stimulation was maximal with indices of hypertrophy and degranulation often more marked in females than in males. In the other group, salmon of the fall run collected in the Pacific Ocean in August had well developed gonads, large gonadotropes and abundant SL cells. In spawning salmon (September) the SL cells were stimulated, mainly in females. However, the final stimulation was less intense than in spring run spawning fish. The SL cells were smaller, without evident granule release, but still abundant in spent salmon of the fall run caught at the end of November. Various factors (time spent in rivers before spawning, starvation, decalcification, stress, hypothalamic influences) were considered which might explain differences between spring and fall run salmon. These observations suggest that SL may play a role in the control of gonadal maturation in chinook salmon as it may also do in sockeye and chum salmon previously studied, and that SL cells may be sensitive to the ambient salinity.     

A unique lipoprotein profile found in the plasma of cultured Japanese eelAnguilla japonica: very low density lipoprotein,but not high density lipoprotein,is the main component of plasma

A unique lipoprotein profile was found in the plasma of cultured Japanese eel,Anguilla japonica which accumulated more lipid in its muscle than in its liver. The plasma lipoprotein level of Japanese eels was in excess of 54 mg ml¹, a concentration considered to be hyperlipoproteinemic in relation to other teleosts. The plasma lipoproteins consisted of very low density lipoprotein (VLDL, density (d)<1.006 g ml¹) low density lipoprotein (LDL, 1.0061), high density lipoprotein 2 (HDL₂, 1.0851), and HDL₃ (1.1001). VLDL, but not HDL, was the main component in the plasma of Japanese eels, unlike most teleosts where HDL is the main component. An additional lipoprotein, vitellogenin (1.2101), was induced by the injection of estradiol-17ß (E₂), but VLDL was the main plasma component even in the E₂-treated eels. VLDL was a triacylglycerol (TG)-rich lipoprotein and possessed two apolipoprotein (apo) B-like proteins of molecular weights (Mr) 260K and 230K as main components.LDL, HDL₂, and HDL₃ were revealed to consist of heterogeneous components by a density gradient ultracentrifugation. LDL was separated into three subclasses of LDL₁ (1.0301), LDL₂ (1.0431), and LDL₃ (1.0671). LDL₁ with apo B-like protein of Mr 230K was a TG-rich lipoprotein, while both LDL₂ and LDL₃ were cholesterol ester-rich lipoproteins with apo A-I-and A-II-like proteins of Mr 25K and 14K. The particle sizes of HDL₂ and HDL₃ subclasses differed, although all of HDL₂ and HDL₃ subclasses possessed apo A-I-and A-II-like proteins of Mr 25K and 14K as main components. To our knowledge, this is the first report of detailed plasma lipoprotein profile in Japanese eels.Corresponding author: till August 18, 1996 and after April 19, 1997: at the above address. From August 19, 1996 till April 18. 1997: c/o Dr. N.H. Haunerland, Department of Biological Sciences. Simon Fraser University, Burnaby, British Columbia, Canada V5A 1S6.     

黑龙江水系(中国)大麻哈鱼生物学特征分析

2010和2011年在黑龙江和乌苏里江生殖洄游群体中采集了571尾大麻哈鱼(Oncorhynchus keta Walbaum)样本,进行了鳞片观察和生物学测定。根据退算叉长,采用Logistic生长方程拟合大麻哈鱼叉长的生长,并计算了生长速度和加速度。结果表明,大麻哈鱼3龄前生长速度较快,以后逐渐变慢。对3+龄大麻哈鱼生长分析表明,在1.372和1.492龄时,雄、雌个体生长速度最快,而在2.674和2.823龄时生长加速度最低,和性成熟开始时期相吻合。利用逻辑斯蒂拟合方程估算了大麻哈鱼50%个体初次性成熟叉长(L50),雄性为46.19 cm,雌性为47.95 cm,ARSS分析表明雌雄差异显著(P<0.05),对应的50%初次性成熟时间T50分别为2.00和2.15。通过大麻哈鱼生长分析,认为应将50%初次性成熟叉长作为资源管理的重要生物学指标。黑龙江大麻哈鱼雌性个体GSI和绝对繁殖力均与叉长呈显著正相关(P<0.05),而雄性个体上述指标均与叉长呈显著负相关(P<0.05)。黑龙江雌性和雄性大麻哈鱼GSI与叉长相关关系的回归方程分别为:y=0.578x–18.225(R2=0.441);y=–0.090x+8.852(R2=0.423)。黑龙江群体性腺发育程度高于乌苏里江群体,乌苏里江群体性腺发育的不一致性导致了GSI和叉长的相关关系不显著。     

An evaluation of the potential influence of SST and currents on the oceanic migration of juvenile and immature chum salmon (Oncorhynchus keta) by a simulation model

Using a salmon migration model based on the assumption that swimming orientation is temperature dependent, we investigated the determining factors of the migration of juvenile and immature chum salmon (Oncorhynchus keta) in the North Pacific. We compared the predictions of the model with catch data of immature and juvenile chum salmon collected by Japanese research vessels from 1972 to 1999. The salmon migration model reproduced the observed distributions of immature chum salmon and indicates that passive transport by wind‐driven and geostrophic currents plays an important role in the eastward migration of Asian salmon. These factors result in a non‐symmetric distribution of Asian and North American chum salmon in the open ocean. The directional swimming component contributes to the northward migration in summer. The model results indicate that during the first winter Asian chum salmon swim northward against the southward wind‐driven currents to stay in the western North Pacific. This suggests that Asian chum salmon require more energy to migrate than other stocks during the first winter of their ocean life.     

Movement of the fluvial form of masu salmon, <Emphasis Type="Italic">Oncorhynchus masou masou</Emphasis>, in a mountain stream in Kyushu,Japan

Using mark-recapture methods, the movements of the fluvial form of masu salmon (Oncorhynchus masou masou) in a mountain stream on the island of Kyushu, Japan, were studied. Most (78%) of the masu salmon were recaptured in the pool in which they had been originally caught and tagged. Of those that moved between pools, the proportion of individuals that moved during the breeding period was not significantly higher than the proportion that moved during the non-breeding period. However, during the breeding period, a higher proportion of larger salmon moved than did smaller fish. The proportion of mobile large males during breeding period was higher than that for small males. Also, it was found that a few individuals showed long-range movement in the autumn. As a long-term movement, 78 individual fish (65%) that were recaptured more than three times showed high sedentary tendencies. Sixteen individual mobile fish (13%) moved and returned to the original pool. Fluvial form of masu salmon in Kyushu show a high sedentary nature; however, large mature males seem to actively move in search of female during breeding period.     

Importance of instream cover for young masu salmon, Oncorhynchus masou, in autumn and winter

Densities of wild masu salmon, Oncorhynchus masou Brevoort, were investigated before (late-September) and after (mid-November) autumnal habitat shifts in a small river in Hokkaido, northern Japan. Abundance of instream cover habitat formed by coarse woody debris, submerged vegetation and undercut banks was quantified. Density of 1+ and older masu salmon was significantly correlated with cover abundance in autumn, although cover was not significant for density of 0+ fish, indicating that clear-cut reaches were utilized by 0+ masu salmon in autumn. In early winter, densities of 0+ and 1+ and older masu salmon were both correlated with cover availability. These results suggest that the amount of cover habitat is an important regulator for densities of juvenile masu salmon during winter.     

Glucose-stimulated lipolysis in rainbow trout,Oncorhynchus mykiss,liver

Rainbow trout, Oncorhynchus mykiss, were used to characterize further the influence of glucose on hepatic lipolysis. Liver was removed from fed fish, cut into 1 mm³ pieces and incubated for up to 5 h in Hanks medium containing either 2 mM, 5.5 mM, 10 mM, or 25 mM glucose. Glucose-stimulated lipolysis was indicated by tissue triacylglycerol (TG) lipase activity and by medium concentrations of glycerol and fatty acids (FA). Triacylglycerol lipase activity in liver pieces incubated in the presence of higher concentrations (25 mM) of glucose was significantly higher than that in liver pieces incubated in lower concentrations (2 mM) of glucose, rising from 0.075 ± 0.002 (mean ± SEM) nmol FA released/h/mg protein to 0.092 ± 0.004 units. Similarly, higher concentrations of glucose stimulated significantly more FA release and glycerol release from liver pieces than that stimulated by lower concentrations of glucose. Glycerol release from liver pieces incubated in the presence of 10 mM glucose and 25 mM glucose was ca. 2-fold to 2.8-fold, respectively, higher than that from liver pieces incubated in the presence of either 2 mM or 5.5 mM glucose. Fatty acid release from liver pieces incubated in the presence of 10 mM or 25 mM glucose was ca. 1.8-fold higher than that from liver pieces incubated in the presence of either 2 mM or 5.5 mM glucose. Notably, increased glycerol release was not accompanied by a parallel increase in FA. Fatty acid reesterification was more pronounced in liver pieces exposed to higher glucose (10 mM and 25 mM) than in liver pieces exposed to lower glucose (2 mM and 5.5 mM). ¹⁴C-incorporation studies indicated that glucose serves as a carbon source for reesterified FA in trout liver. The route of reesterification appears to be from glucose to glycerophosphate to phosphatidic acid to diacylglycerol to TG. Increasing concentrations of glucose did not affect glycerol kinase activity, indicating that glucose-stimulated lipolysis was not accompanied by increased glycerol recycling within the liver. These results suggest that glucose stimulates fatty acid reesterification and directly enhances net lipolysis in trout liver incubated in vitro.A part of this study was presented at the Annual Meeting of the American Society of Zoologists, December 26–30, 1991, Atlanta, GA.     

Relationship between coastal water properties and adult return of chum salmon (Oncorhynchus keta) along the Sanriku coast,Japan

We investigated the relationship between adult (age‐4) return rates for chum salmon (Oncorhynchus keta) originating from the Iwate Prefecture, Japan, and coastal environmental conditions during their early ocean life in coastal residency. We analyzed distributions of water properties via intensive hydrographic observations using a conductivity–temperature–depth profiler. Both the return rates and water properties vary strongly over interannual time scales. We found that the time when the return rate decreased drastically corresponded well to the time when the frequency of warm waters in the coastal residency increased.     

White muscle of masu salmon,Oncorhynchus masou masou,smolts possesses a strong buffering capacity due to a high level of anserine

Masu salmon, Oncorhynchus masou masou, fry were fed with diets containing three different levels of protein for 18 weeks, and the levels of free amino acids and related compounds in the white muscle were compared among the dietary groups and between smolts and parr. The anserine level in the white muscle of smolts was always higher than that of parr, while histidine and glycine levels in the former were always lower than those in the latter, irrespective of dietary treatments. A mixed solution of crystalline anserine, histidine and glycine simulating these amino acid levels in the white muscle of the smolts had a stronger buffering capacity in the physiological pH range than that simulating those levels present in parr. These results suggest that even in freshwater conditions, the white muscle of smolts possesses a more potent buffering capacity than the muscle of parr, for anaerobic burst swimming during the downstream migration. Moreover, the white muscle of smolts fed the high-protein diet had a significantly higher level of anserine than that of smolts fed the low- or intermediate-protein diets, and the solution mimicking the white muscle of smolts fed the high-protein diet showed the strongest buffering capacity among the mixed solutions tested. Thus, a diet with high-protein level could improve qualities of smolts.     

国内虹鳟代表性养殖群体的高通量SNP芯片检测及遗传分析

本研究旨在对国内虹鳟(Oncorhynchus mykiss)代表性养殖群体开展全基因组水平的遗传评估。利用57K单核苷酸多态性(single nucleotide polymorphism,SNP)芯片,检测了来自不同地域的6个虹鳟养殖群体样本共计48尾,包括黑龙江虹鳟、黑龙江金鳟、四川虹鳟、四川金鳟、北京虹鳟和北京金鳟,共获得有效SNP位点50201个,在中国虹鳟中的多态比例达到97.7%,表明该芯片虽然基于美国和挪威虹鳟群体设计,但对中国群体同样具有良好的适用性。各群体最小等位基因频率均值为0.240~0.267,与国外主流养殖群体相近,黑龙江虹鳟、四川虹鳟和北京虹鳟群体内遗传多样性丰富,多态位点比例为83.6%~84.9%,与国外主流养殖群体相近,而黑龙江金鳟、四川金鳟和北京金鳟,多态位点比例相对较低,在60.2%~76.9%范围内。应用6个中国虹鳟群体和2个美国虹鳟群体数据开展系统发育分析、主成分分析和群体遗传结构STRUCTURE分析,结果显示8个群体可分为3个祖源类群,其中3个金鳟群体为遗传联系较紧密的一个类群,黑龙江虹鳟和北京虹鳟为一个类群,而四川虹鳟与2个美国虹鳟群体为一个类群,部分中国养殖群体中有显著离群个体存在,表明群体遗传背景不均一。本研究表明,高密度SNP芯片在我国虹鳟养殖群体遗传分析中具有广泛的应用前景,能够为种质资源评估、本土化良种培育、制种和引种工作提供基因组水平的参考信息。     

虹鳟源嗜冷黄杆菌的分离鉴定及致病性研究

为确定患病虹鳟的病原,本实验从患病鱼溃烂肌肉中分离到2株细菌,分别命名为CH06和CH07,经回归感染证实分离菌株为导致此次虹鳟患病的病原菌,并进一步对其形态特征、理化特性、分子特征、血清型及耐药性进行分析。结果显示,CH06和CH07株在TYES琼脂平板上呈煎蛋状外观,产黄色素,氧化酶和过氧化氢酶呈阳性,能水解明胶和酪蛋白,不能水解淀粉,不能利用果糖、半乳糖和七叶苷等。16S rRNA比对结果显示,CH06和CH07株与嗜冷黄杆菌模式株NBRC 15942的同源性分别为99.35%和99.42%。综合菌株理化和分子特性确定CH06和CH07株为嗜冷黄杆菌。利用多重PCR方法鉴定CH06和CH07株的血清型均为1型(Fd型);多位点序列分型(MLST)分析表明,CH06和CH07株的基因型分别为ST-12和ST-78型,且均属于CC-ST10克隆型。人工感染结果显示,CH06和CH07株对虹鳟幼鱼具有较高致病性,其半致死浓度(LD₅₀)分别为7.1×10⁵和1.1×10⁵ CFU/mL,攻毒剂量与临床病症出现时间呈反比,从人工感染实验鱼的肌肉、脾脏等组织中可重新分离到嗜冷黄杆菌。组织病理变化显示,病鱼肝细胞肿胀,空泡变性,部分肝细胞溶解坏死,细胞核溶解消失;脾脏充血、出血,淋巴细胞减少,红细胞和含铁血黄素增多;肌纤维间隙增宽、断裂、弯曲不齐,部分肌细胞肌浆溶解呈蜂窝状。CH06和CH07株对10种抗菌药物的耐药谱略有不同,均对氨苄西林和甲氧苄啶-磺胺甲噁唑敏感;CH06株对恩诺沙星、氟苯尼考等耐药,而CH07株对恩诺沙星和氟苯尼考中度敏感。本研究首次报道了我国虹鳟源嗜冷黄杆菌的分离鉴定及生物学特性,以期为虹鳟细菌性冷水病的防控提供科学依据。     

大西洋鲑、三倍体虹鳟和金鳟的肌肉营养成分与品质特性

为了解大西洋鲑(Salmo salar)、三倍体虹鳟(Oncorhynchus mykiss)、金鳟(Oncorhynchus mykiss)3种鱼肌肉营养成分和品质特性,利用生化分析、物性分析方法分析3种鱼肌肉的营养成分、氨基酸和脂肪酸组成、肉色、系水力和质构特性。结果表明,大西洋鲑、三倍体虹鳟、金鳟肌肉的水分质量分数分别为62.91%、67.15%、73.02%,粗蛋白质量分数分别为22.39%、21.03%、22.11%,粗脂肪质量分数分别为14.64%、17.16%、5.11%。3种鱼肌肉的滴水损失、黄色值(b~*)、羟脯氨酸含量、内聚性均显著不差异(P0.05)。3种鱼肌肉的硬度和咀嚼性由低到高依次为大西洋鲑、三倍体虹鳟、金鳟,而pH值的结果则与之相反(P0.05)。大西洋鲑和三倍体虹鳟肌肉的灰分、解冻损失、蒸煮损失、回复性、弹性和红色值(a~*)差异不显著(P0.05),但灰分、蒸煮损失、回复性均小于金鳟肌肉的对应指标(P0.05),弹性和红色值(a~*)则均大于金鳟肌肉的对应指标(P0.05)。大西洋鲑、三倍体虹鳟、金鳟肌肉中必需氨基酸含量占氨基酸总量分别为42.28%、41.84%、41.63%(质量分数),必需氨基酸/非必需氨基酸(EAA/NEAA)比值分别为73.25%、71.94%、71.32%,均符合联合国粮农组织/世界卫生组织(FAO/WHO)对优质蛋白质的评价标准;3种鱼肌肉中均检测到22种脂肪酸,组成丰富,其中不饱和脂肪酸含量较高。综上所述,3种鱼的肌肉都是符合人体营养需求的优质水产品,其中大西洋鲑和三倍体虹鳟肉质接近,且都优于金鳟的肉质。     

Change in chum salmon (Oncorhynchus keta) stomach contents associated with fluctuation of pink salmon (O. gorbuscha) abundance in the central subarctic Pacific and Bering Sea

The abundance and stomach contents of salmonids (Oncorhynchus spp.) and the biomass of prey organisms were examined in the central subarctic Pacific and Bering Sea in the summer of 1991 and 1992. Salmonids were caught by surface longline using the same level of fishing effort. Chum (O. keta) and pink (O. gorbuscha) salmon were the predominant species, representing 44% and 36% sof the total catch (n = 1275) in 1991. In 1992, chum salmon composed 85% of the total catch (n = 603), but the catch of pink salmon decreased to 1% of the total catch due to the odd/even year fluctuation of Asian pink salmon abundance in the study area. It was found that chum salmon changed their dominant diet from gelatinous zooplankton (pteropods, appendicular-ians, jellyfishes, chaetognaths, polychaetes and unidentified materials) in 1991, when pink salmon were abundant, to a diet of crustaceans (euphausiids, cope-pods, amphipods, ostracods, mysids and decapods) in 1992, when pink salmon were less abundant. Local crustacean biomass (wet weight; mg m^-3) had significant negative correlation with the CPUE (catch number per 30 hachi) of pink salmon in 1991 (r = -0.586; P = 0.026) and that of chum salmon in 1992 (r =–0.616; P = 0.014). There may be a limitation in the available prey resource for production of salmonids.