Genetic divergence of kingfish from Japan, Australia and New Zealand inferred by microsatellite DNA and mitochondrial DNA control region markers

ABSTRACT: Genetic polymorphism in kingfish, collected from coastal waters of Japan, Australia and New Zealand, were examined using microsatellite (MS) DNA and mitochondrial DNA (mtDNA) control region markers. Sixteen to 25.7 alleles per locus were observed in three MS markers, while the average observed (and expected) heterozygosities were 0.782 (0.918), 0.750 (0.809) and 0.650 (0.888) for Australian, Japanese and New Zealand kingfish, respectively. Twelve mtDNA haplotypes were detected by the digestion of control region sequences with five endonucleases: Hae III, Hinf I Mbo I, Rsa I and Taq I. Significant genetic divergence was observed between the kingfish population from Japan and those from Australia–New Zealand. There was no significant differentiation among the Australian and New Zealand population samples.     

Seasonal changes in proteolytic enzymes of yellowtail Seriola quinqueradiata (Temminck & Schlegel; Carangidae) fed extruded diets containing different protein and energy levels

Seasonal variations in pepsin, trypsin and chymotrypsin activities and protein digestibility were studied in yellowtails (Seriola quinqueradiata) reared for 1 year with extruded diets containing different levels of protein. Trypsin and chymotrypsin storage levels in the digestive tissues of starved fish were affected by seasonal changes in water temperature. Actual digestion activities of trypsin and chymotrypsin were low at lower water temperatures, but pepsin activity in the stomach tissue was not affected by low temperatures. On the other hand, trypsin and chymotrypsin activities in the intestinal contents were higher during lower water temperature months, while pepsin activity in the stomach contents was low at lower water temperatures. Apparent protein digestibility (APD) did not differ among the dietary treatments in the higher water temperature months, while in colder months it was higher in fish fed diet 1 than in fish fed diets 2 and 3. The APD values reflected pepsin activity in the stomach contents in all sampling months. Therefore, lower APD in colder months seems to be attributed to lower protease activity in the gastric digesta, implying that enhanced pepsin secretion from the stomach tissue might improve protein digestibility and growth performance in yellowtails during winter.     

The abundance of juvenile yellowtail (Seriola quinqueradiata) near the Kuroshio: the roles of drifting seaweed and regional hydrography

We assess the effect of drifting seaweed (Sargassum sp.) biomass, geography and hydrography on juvenile yellowtail (Seriola quinqueradiata) abundance variation off the southeast coast of Japan, near the Kuroshio Current. The amount of drifting seaweed mats progressively increased northeastward into the cooler, coastal waters. Frontal structure indexed using a station‐to‐station ΔSST did not explain spatial variation in the seaweed mat distribution, although the western extent of the Kuroshio Current appeared to act as a boundary. Juvenile yellowtail constituted 51–62% of the fish collected in association with drifting seaweed mats in April 1996 and 1997 and 29% in June 1996. The abundance of juvenile yellowtail was positively correlated with seaweed biomass. The geographic distribution of juvenile yellowtail associated with drifting mats varied among sampling periods, being more southwesterly in April and more northeasterly in June. Simple multiple regression models based on seaweed biomass and geographic distribution (latitude) explained between 35% and 43% of the variation in juvenile yellowtail abundance in spring. Associations with spatial and temporal variations in hydrographic conditions did not contribute to explained variation in a meaningful manner. The results presented here indicate that, off the southeast coast of Japan during April, yellowtail juveniles are likely to be most abundant when seaweed biomass is high, occur offshore, and are bounded by the western extent of the Kuroshio Current near the 19–20°C SST isotherm.     

黄条魳(Seriola aureovittata)肌肉营养组成分析与评价

为进一步认识和评价黄条(Seriola aureovittata)的营养与食用价值,本研究测定了其肌肉中的水分、蛋白质、粗脂肪、灰分、氨基酸、脂肪酸和矿物质等成分,并对其养殖及野生个体的肌肉营养成分组成进行了比较分析.结果显示,黄条肌肉中蛋白质含量较高,必需氨基酸和鲜味氨基酸含量丰富,完全符合FAO/WHO推荐的理想蛋白质标准,是一种优质蛋白供给源.根据AAS和CS分值,黄条肌肉的第一限制氨基酸为蛋氨酸,第二限制氨基酸为缬氨酸.黄条肌肉的脂肪含量高于三文鱼(Salmo salar)、金枪鱼(Thunnus thynnus)、石斑鱼(Epinephelus sp.)等,且肌肉中含有丰富的不饱和脂肪酸,不饱和脂肪酸与饱和脂肪酸比值较高,特别是EPA+DHA的含量高,具有较优的口感鲜度和较高的营养价值.另外,黄条肌肉中含有多种机体新陈代谢所需的矿物质,经常食用可促进人体新陈代谢水平.比较发现,养殖黄条较野生黄条具有相对较高的脂肪含量和较低的水分含量,比能值(EP)分别为13.44 kJ/g和8.68 kJ/g,其他营养成分无显著差异,表明养殖与野生黄条肌肉营养价值相似.综上所述,黄条肌肉蛋白质和脂肪质量较高,口感鲜美,营养成分丰富,是一种值得大力开发养殖的海产经济鱼类.     

黄条魳(Seriola aureovittata)形态度量与内部结构特征

为了全面认识黄条(Seriola aureovittata)生物学特性,利用传统测量方式、框架测度法、几何形态测量法和解剖学方法,观察和测度了其外部形态特征、可量与可数性状及内部结构特征,并模拟构建了黄条形态性状度量框架图.观察了黄条不同部位鳞片和耳石形态特征,比较了各形态度量性状的比值关系,发现全长与体长比值、下颌长与上颌长比值、尾柄长与尾柄高比值变异较小,表明这些性状关联密切.利用统计分析方法建立了黄条全长(TL)与体重(BW)之间的关系模型:BW=2.1652TL2-140.35TL+2479.9 (R2=0.9812),体高(BH)与体重间的关系模型:BW=0.7575BH30059(R2=0.9816).研究分析表明,在黄条的12个可量形态性状中,除眼径外的其他11个形态性状间均存在显著相关关系.通径分析进一步揭示了体高和体长性状是影响体重的2个关键因素,其对体重的决定程度分别达41.34％和13.11％,它们对体重的共同决定程度达42.88％.本研究观察描述了黄条内部结构特征,其比肠长为0.62-0.69,脊椎骨数量为23-25,总出肉率可达75％.本研究结果可为黄条种质判别、系统分类及人工繁育与养殖技术开发提供形态认知依据.     

Nutritional evaluation of rotifers in rearing tanks without water exchange during seed production of amberjack <Emphasis Type="Italic">Seriola dumerili</Emphasis>

We evaluated the nutrient contents of rotifers sampled from larval-rearing tanks (tank rotifers) without water exchange during the seed production of amberjack Seriola dumerili at three facilities (Kamiura, Kagoshima, and Miyazaki) and compared them with the nutrient contents of freshly enriched rotifers. Compared to the enriched rotifers, the lipid contents, especially neutral lipids and proportion of 22:6n-3, tended to decrease in the tank rotifers. These trends were clearer at Miyazaki where the tank rotifers were sampled before daily supplementation of microalgae (Nannochloropsis). Crude protein content of the tank rotifers did not decrease markedly although the proportion of lysine tended to decrease. Vitamin C and E contents of the tank rotifers decreased significantly only at Miyazaki. Calcium content of the tank rotifers increased at Kamiura and Miyazaki, and the increases in iron and manganese contents of the tank rotifers at Miyazaki and zinc content at Kagoshima were pronounced. These results suggest that the nutritional value of rotifers in larval-rearing tanks without water exchange can be maintained by appropriate supplementation of microalgae. The effect of certain minerals that became high in tank rotifers on subsequent larval development requires further investigation.     

黄条鰤 igfbp-1和igfbp-2基因克隆、表达及其生长调控作用

胰岛素样生长因子结合蛋白(insulin-like growth factor binding proteins, IGFBPs)在调节胰岛素样生长因子的生物学活性和生长调控中起着至关重要的生理作用。本研究克隆了黄条鰤(Seriola aureovittata) igfbp-1、igfbp-2a和igfbp-2b等3个基因cDNA编码的开放阅读框(ORF)序列,分析了其组织分布特征,并检测了工厂化不同养殖密度下黄条鰤肝脏中5个基因igfbp-1、igfbp-2a、igfbp-2b、igf-1和igf-2对生长的调控作用。结果显示,igfbp-1的ORF长为741 bp,共编码246个氨基酸;igfbp-2a的ORF长度为882 bp,共编码293个氨基酸;igfbp-2b的ORF长度为810 bp,共编码269个氨基酸。它们均具有广泛的组织表达特性,其中在肝脏中显著高表达,且具有性别二态性表达特性。工厂化养殖条件下,低密度组实验鱼生长速度最快且igfbp-1、igfbp-2a、igfbp-2b、igf-1和igf-2表达量均最高,与中、高密度组有显著性差异(P<0.05),且与血清IGF-1、GH表达趋势相同,与皮质醇含量及葡萄糖浓度的趋势相反;而中、高密度组实验鱼的生长及igfbp-1、igfbp-2a、igfbp-2b、igf-1和igf-2表达量均无显著差异。本研究表明,igfbp-1、igfbp-2a和igfbp-2b参与了不同养殖密度下黄条鰤生长的调控过程,且与igf-1、igf-2对生长的表达调控存在正向协同效应。研究结果为阐释黄条鰤生长的分子机制以及工厂化条件下适宜养殖密度的调控提供了理论依据。     

黄条鰤仔稚幼鱼消化酶活性变化研究

为了解黄条鰤(Seriola aureovittata)早期发育阶段的消化生理特性,测定了黄条鰤胚胎、仔稚幼鱼阶段脂肪酶、淀粉酶、胰蛋白酶和碱性磷酸酶活性变化。结果显示,在黄条鰤仔鱼出膜前胚胎阶段,即能检测到脂肪酶、淀粉酶和碱性磷酸酶活性;初孵仔鱼体内(1 d)初次检测出胰蛋白酶的活性。脂肪酶和碱性磷酸酶比活力在仔鱼孵化后迅速增强(P<0.05),在4 d开口时,2种酶比活力达最高值;淀粉酶比活力在7 d时达最大值;胰蛋白酶比活力在仔鱼阶段缓慢上升,15 d时比活力最大。稚鱼阶段内脏团中脂肪酶、碱性磷酸酶和胰蛋白酶活性基本维持稳定,幼鱼阶段内脏团脂肪酶、碱性磷酸酶和胰蛋白酶活性都呈现上升趋势;稚鱼和幼鱼阶段内脏团中淀粉酶活性下降并基本稳定于较低水平。研究表明,黄条鰤仔稚幼鱼发育过程中,各种消化酶活性变化明显,且与其发育阶段和食性密切相关。在尚未摄食饵料的早期仔鱼体内已存在消化酶,认为其是母源传递而来,不是由外源性饵料所致;幼鱼阶段内脏团脂肪酶、碱性磷酸酶和胰蛋白酶比活力明显提高,这反映出随苗种生长发育,其肠道结构和消化机能逐渐完善,并且对脂肪、蛋白质的需求逐渐增强。     

Lancefield group C Streptococcus dysgalactiae infection responsible for fish mortalities in Japan

A Lancefield serological group C Streptococcus sp. was isolated from cultured amberjack, Seriola dumerili Risso, and yellowtail, Seriola quinqueradiata Temminck and Schlegel, immunized with Lactococcus garvieae commercial vaccines in Japan. The isolated bacteria were Gram-positive cocci, auto-aggregating in saline, morphologically long chains in growth medium, catalase negative and alpha-haemolytic on blood agar. An almost complete gene sequence of the 16S rDNA of two isolates was determined and compared with that of bacterial strains in the database. The isolates were identified as Streptococcus dysgalactiae based on the results of the 16S rDNA sequence, the bacteriological properties and the Lancefield serological grouping. Oligonucleotide primers specifically designed for the 16S-23S rDNA intergenic spacer region of S. dysgalactiae amplified a gene from all the fish isolates, as well as the type strains alpha-haemolytic S. dysgalactiae subsp. dysgalactiae ATCC430738 and beta-haemolytic S. dysgalactiae subsp. equisimilis ATCC35666, but not those of S. equi ATCC33398, Lactococcus garvieae ATCC43921 and L. garvieae KG9408. The severe necrotic lesions of the caudal peduncle seen in experimentally infected fish were similar to those seen in naturally infected fish.