Metabolic biochemistry of cardiac muscle in three tuna species (bigeye, Thunnus obesus ; yellowfin, T. albacares ; and skipjack, Katsuwonus pelamis ) with divergent ambient temperature and oxygen tolerances

Bigeye tuna (Thunnus obesus) have much greater vertical mobility than yellowfin (T. albacares) and skipjack (Katsuwonus pelamis) tunas, due to an apparent greater tolerance of the changes in ambient temperature and oxygen occurring with depth. In an attempt to identify physiological processes (e.g., effects of temperature on cardiac function) responsible for these behavioral differences, we examined enzyme activities (at 12 °C, 17 °C, and 25 °C) of cardiac muscle in all three species. Contrary to our expectations, we found few differences and no clear explanatory patterns in maximum enzyme activities (V_max) or enzyme activity ratios. For example, citrate synthase (CS) activity was the same in bigeye and skipjack tunas, but 40% lower in yellowfin tuna, whereas carnitine palmotoyltransferase (CPT) activity in skipjack tuna was approximately double that in the other two species. The ratio of CPT to pyruvate kinase (PK) activity, a measure of the tissues preference for fatty acids as metabolic substrates, was the same in bigeye and yellowfin tunas, but elevated skipjack tuna. The ratios of lactate dehydrogenase (LDH) to CS activity and of PK to CS activity (anaerobic–aerobic enzyme activity ratios – taken as measures of the tissues ability to tolerate hypoxia) were both elevated in yellowfin tuna cardiac tissue relative to the other two species. We also found no differences in temperature sensitivity (Q₁₀ values) when comparing cardiac enzyme activities across species, nor effects of temperature on the substrate affinity (K_m) of LDH. In sum, our results do not suggest any clear metabolic difference in the cardiac muscle that would explain the apparent greater tolerance of bigeye tuna to acute hypoxia and ambient temperature changes or their substantially greater vertical mobility.     

Development of a simple method for sperm cryopreservation of Scombridae fishes in outdoor environments

We developed a simple dry shipper method for cryopreserving the sperm of Scombridae fish in outdoor environments. First, we undertook a preliminary study to optimize the sperm cryopreservation conditions using bullet tuna, Auxis rochei (Risso, 1810) sperm. We found that the optimum cryomedium contained 90% foetal bovine serum (FBS) or 300 mM trehalose as an external cryoprotectant and 10% dimethyl sulfoxide (DMSO) as an internal cryoprotectant. Under these optimized conditions, the post‐thaw sperm had a duration of motility of 500 s and a motility rate of >70%. We then performed practical trials of the optimized protocol in various outdoor environments (e.g., fishing boats and ports) using the sperm of five Scombridae species: chub mackerel, Scomber japonicus (Houttuyn, 1782); blue mackerel, S. australasicus (Cuvier, 1832); skipjack tuna, Katsuwonus pelamis (Linnaeus, 1758); longtail tuna Thunnus tonggol, (Bleeker, 1851) and Pacific bluefin tuna, T. orientalis (Temminck & Schlegel, 1844). The post‐thaw sperm of all five of these species had a duration of motility of 650 s and a motility rate of >70%, indicating that this simple method can be used to obtain high‐quality cryopreserved sperm of various Scombridae species in outdoor environments.     

基于形态和分子标记的三种鲭科鱼类鉴别新方法

为找到日本鲭(Scomber japonicus)、澳洲鲭(S.australasicus)和羽鳃鲐(Rastrelliger kanagurta)这三种鲭科鱼类鉴别的新标记,采用形态框架等形态分析方法和线粒体标记的方法开展研究.共分析采自海南的33 ind样本,其中日本鲭19 ind,澳洲鲭9 ind,羽鳃鲐5 in...     

两种鲭科以及其他鱼类松果体窗形态结构的比较

为了解鲭科鱼类颅顶松果体窗的结构和其与生活习性、鱼类系统进化的关系、利用光镜、X射线同步辐射技术以及组织石蜡切片技术观察了黄鳍金枪鱼（Thunnus albacares）和日本鲐鱼渊（Pneumatophorus japonicus）松果体窗的组织学结构。此外,通过随机取样分属9目17科的20种鱼类标本,检测松果体窗形态结构,分析松果体窗与鱼类进化发育的关系,并探讨其在鱼体可能发挥的生理功能。研究结果表明,具松果体窗的鱼类大都居于近海或淡水水域的底层,松果体窗的产生与它们的生存环境有一定关系,这种特殊的生理结构可以使鱼类在弱光环境中尽可能多地接受光线,让光线到达大脑并调节生理功能。同时,具有洄游特性的海洋鱼类也具有松果体窗结构,这种结构有利于鱼类通过感知光线的变换来确定洄游路线。     

基于线粒体 Cyt b 和 ITS1 部分序列分析鲭科鱼类分子系统进化关系

鲭科(Scombridae)由15属51种表层洄游性海洋鱼类组成,广泛分布于热带和亚热带海域,是重要的经济鱼类。目前关于鲭科鱼类系统发生学的研究主要基于形态学特征。为了从分子水平上阐明鲭科鱼类的分类与系统进化关系,本研究扩增了鲭科7种鱼类的线粒体细胞色素b(Cyt b)基因1个含311个碱基的序列区和转录间隔区1(ITS1)的1个含644～692个碱基的序列区。采用多个生物软件对序列碱基组成进行分析,计算了Kimura-2parameter遗传距离、转换/颠换比等遗传信息指数。Cyt b和ITS1序列4种碱基平均含量分别是:A为22.8%、G为16.4%、C为31.2%、T为29.5%和A为13.5%、G为31.3%、C为38.7%、T为16.5%。基于Cyt b计算的鲭科鱼类种间遗传距离为0.0065～0.3335,平均遗传距离为0.1689;基于ITS1计算的金枪鱼族鱼类种间遗传距离为0.0032～0.2668,平均遗传距离为0.2025。Cyt b和ITS1序列的转换/颠换比分别为1.8和0.9。以竹荚鱼(Trachurus trachurus)和花鲈(Lateolabrax japonicus)为外群,并结合GenBank上鲭科24种鱼类的同源序列,构建NJ、ML和ME系统树。研究结果确认了金枪鱼属处于系统进化树的顶端,代表着最新演化的种类,是鲭科中最繁盛的一属,也是目前系统发育的高峰。所有分子系统树都表明鲣属、鲔属和舵鲣属显示与金枪鱼属很近的亲缘关系,它们均归入金枪鱼族。然而,研究结果与形态学上将金枪鱼属分为2个亚属的分类结果存在分歧。同时,本研究关于狐鲣属、平鲣属、刺鲅属和双线鲅属进化地位上的结果也不同于形态学的结果。故鲭科鱼类客观、科学的分类地位还需通过形态学、生态学和分子生物学的深入研究加以确认。