低盐胁迫对红鳍东方鲀幼鱼肝脏的酶活性、组织结构及免疫基因表达的影响

为探讨低盐胁迫下肝脏在红鳍东方鲀(Takifugu rubripes)机体免疫中的作用,在肝脏酶活性、组织结构和基因表达水平3个方面进行了研究。结果表明,低盐(盐度4‰)胁迫下红鳍东方鲀肝脏中总超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、酸性磷酸酶(ACP)和碱性磷酸酶(AKP)的酶活性显著高于对照组(P0.05);肝脏组织结构中肝细胞发生肿大,形状变形;肝脏IL15和TLR3基因的表达量显著升高(P0.05),而IRF2基因的表达量却未有显著性差异(P0.05)。     

红鳍东方鲀3个白介素基因的序列特征及表达分析

本试验分析体质量(190.34±2.13)g的红鳍东方鲀白介素基因IL-1b、IL-8和IL-10的序列特征,检测其在红鳍东方鲀脑、鳃、心脏、肌肉、肝脏和脾脏中的表达,以及每尾红鳍东方鲀注射密度1×10^7 cfu/mL的哈维氏弧菌菌液0.1 mL后0、12、24、48 h在肝脏和脾脏中的表达。试验结果表明,IL-1b、IL-8和IL-10基因的序列全长分别为771、822 bp和844 bp。3个基因在健康成鱼脑、鳃、心脏、肌肉、肝脏、脾脏中均有表达,其中肝脏和脾脏表达显著(P<0.05)。感染哈维氏弧菌后12 h,IL-1b基因在肝脏中显著上调,12 h和48 h在脾脏中显著升高(P<0.05)。感染哈维氏弧菌后12 h和24 h IL-8基因在肝脏和脾脏中均显著上调(P<0.05);而感染后24 h和48 h IL-10基因在肝脏中显著升高,在脾脏中12 h和48 h显著升高(P<0.05)。笔者首次探讨红鳍东方鲀IL-1b、IL-8和IL-10基因的序列特性及表达特征,为研究3个基因的原核表达提供了试验信息,将为进一步深入探究重组蛋白活性及其在红鳍东方鲀健康养殖中的应用奠定基础。     

不同LED光谱对红鳍东方鲀幼鱼生长、摄食及消化酶活性的影响

为探究不同 LED 光谱对红鳍东方鲀(Takifugu rubripes)幼鱼摄食、生长发育和生理活性的影响, 选取 525 尾红鳍东方鲀幼鱼养殖在海水循环水养殖系统中, 分别用 5 种不同 LED 光谱(红、黄、蓝、绿、白)照射处理 30 d, 光周期为 12 L : 12 D, 实验期间测定饵料转化效率, 实验结束时测定其存活、生长指标及消化酶活性。结果表明, 不同 LED 光谱对红鳍东方鲀幼鱼的存活、生长和摄食的影响具有显著性差异(P＜0.05)。其中绿光组红鳍东方鲀的存活率最高, 为(65.71±0.00)%; 绿光组红鳍东方鲀幼鱼体重最大, 为(29.36±3.78) g。在饵料转化效率方面, 绿光组幼鱼的饵料转换效率显著高于其他各组(P＜0.05)。在消化酶活性方面, 不同 LED 光谱处理组中红鳍东方鲀幼鱼的消化酶活性均存在显著性差异(P＜0.05), 其中绿光组的酸性磷酸酶、碱性磷酸酶、己糖激酶、丙酮酸激酶活性均显著高于其他各处理组(P＜0.05); 绿光组肝脂肪酶活性较高, 显著高于蓝光与黄光组(P＜0.05); 绿光组肠脂肪酶活性显著高于红光、白光组(P＜0.05)。综上所述, 绿光对红鳍东方鲀幼鱼的生长发育具有较好的促进作用。     

重组IFN-γ免疫后红鳍东方鲀免疫相关基因在肾组织中的表达分析

为探讨重组红鳍东方鲀(Takifugu rubripes)干扰素γ(rIFNg-γ)对机体的免疫应答,以不同浓度(25μg/mL rIFNg-γ为实验组1、50μg/mL rIFNg-γ为实验组2)的原核表达的IFN-γ重组蛋白免疫6月龄健康红鳍东方鲀,PBS作为对照组,于腹腔注射后6、12、24、36h取肾脏组织。实时定量PCR检测肾组织IFN-α、IFN-γ、MHCⅠ、Mx1基因在肾脏组织不同时间表达量的差异。结果显示,红鳍东方鲀经rIFNg-γ免疫后6～36h,IFN-α基因在实验组1中的表达呈现先上升后下降的趋势,24h时表达量最高;在实验组2中的表达量在6h最高,随后呈下降趋势。IFN-γ、MHCⅠ在免疫后6h表达量都出现最大值且实验组1高于实验组2,随后呈下降趋势。Mx1基因的表达则出现上升趋势,24h时表达量最高,随后下降。     

红鳍东方鲀、菊黄东方鲀及其杂交F1幼鱼耗氧率与窒息点研究

利用封闭呼吸室对同一日龄、不同规格的红鳍东方鲀、菊黄东方鲀和菊黄东方鲀(♀)×红鳍东方鲀(♂)杂交F1代幼鱼进行耗氧率和临界窒息点的研究。试验结果表明,水温14.8～15.6℃时,体质量(37.24±3.64)g的红鳍东方鲀幼鱼耗氧率为(0.3385±0.0161)mg/(g.h),体质量(14.45±1.08)g的菊黄东方鲀幼鱼耗氧率为(0.2327±0.0241)mg/(g.h),体质量(27.96±1.38)g的杂交F1代东方鲀幼鱼耗氧率为(0.2282±0.0219)mg/(g.h);同一日龄不同规格红鳍东方鲀、菊黄东方鲀和杂交东方鲀幼鱼的耗氧量分别为(12.5243±0.6720)、(3.3544±0.2975)、(5.8469±0.9537)mg/(h.尾);3种东方鲀的耗氧率呈明显的昼夜节律,白天平均耗氧率显著高于夜晚。水温为14.8～15.6℃时,红鳍东方鲀、菊黄东方鲀及杂交东方鲀幼鱼的临界窒息点分别为0.665、0.882mg/L和0.774mg/L。     

红鳍东方鲀AFP、CIRP、HMGB1和YB-1基因对低温胁迫的响应

鱼类的生长和繁殖受环境条件的调节,冬季的低温会给红鳍东方鲀(Takifugu rubripes)产业带来不利影响。为研究红鳍东方鲀耐低温机制,本研究利用实时荧光定量PCR技术,分析抗冻蛋白(AFP)基因、冷诱导RNA结合蛋白(CIRP)基因、高速迁移蛋白家族蛋白(HMGB1)基因、Y-box结合蛋白(YB-1)基因在不同温度条件下(18℃、13℃、8℃和5℃),在红鳍东方鲀的肝、脾、肾、脑、心、肠、肌肉、性腺和皮肤中的表达情况。结果显示,AFP基因呈广泛性表达,在肌肉中表达量最高(P<0.05),随着温度的降低,各组织中AFP基因的表达量基本呈显著升高的趋势,在5℃组达到最高值,显著高于对照组(P<0.05)。CIRP基因在肌肉中表达量最高(P<0.05),随着温度的降低,各组织中CIRP基因的表达量的升降程度有所不同,在肝、肾、脑、心、肠、皮肤中的表达量呈先升高后降低再升高的趋势,在脾、肌肉和性腺中表达量呈上升趋势。HMGB1基因在肌肉中表达量最高(P<0.05),在脑、心、肝和皮肤中也有较高的表达量;随着温度的降低,除肝脏外,各组织中HMGB1基因的表达量基本呈先升高后降低的趋势,并在8℃组达到最大值,显著高于其他各组(P<0.05)。YB-1基因在肌肉中表达量最高(P<0.05),在其他组织中表达量较低;随着温度的降低,大部分组织中(脑、心、肠、肾、肝、肌肉和脾)表达量呈先升高后降低再升高的趋势,在8℃组达到最小值(P<0.05)。以上结果表明,4种基因表达水平因组织、温度的不同而不同,反映了这4种基因的功能特异性;在低温胁迫下,4种基因积极响应,表达量均发生不同程度的变化,表明4种基因在红鳍东方鲀低温环境适应中可能具有潜在的重要作用。另外,从表达变化规律来看,8℃可能是红鳍东方鲀应对低温胁迫的关键调控点,过低的温度会造成其调控紊乱,这可为研究红鳍东方鲀低温应答调控机制提供相关依据。     

盐度、pH对文蛤肌肉、鳃、外套膜HSP70基因表达的影响

为探讨池塘养殖文蛤的适宜盐度和pH范围,以β-actin为内参基因,采用实时荧光定量聚合酶链式反应技术,检测不同盐度(16、18、20、22、24)和pH(6.7、7.7、8.7、9.7、10.7)梯度下文蛤肌肉、鳃、外套膜中HSP70基因mRNA的表达水平。结果显示,盐度16、18、22、24处理组肌肉中HSP70基因的表达量显著高于盐度20的对照组(P0.05);除盐度18组鳃和盐度24组外套膜HSP70基因的表达量与对照组差异不显著外(P0.05),16、18、22、24盐度组鳃和外套膜中HSP70基因的表达量均显著高于对照组(P0.05)。pH 6.7、7.7、9.7、10.7处理组肌肉、鳃、外套膜中HSP70基因的表达量与pH为8.7的对照组差异显著(P0.05)。试验结果表明,超出一定盐度、pH范围,可显著诱导文蛤肌肉、鳃、外套膜中HSP70基因的过量表达,研究结果可为池塘文蛤的健康养殖提供参考。     

红鳍东方鲀伪雌鱼卵巢发育迟滞的调控机制

伪雌鱼的培育是红鳍东方鲀(Takifugu rubripes)全雄制种技术研发的关键环节之一,然而外源雌激素诱导获得的伪雌鱼表现出卵巢发育迟滞,降低了其育种价值和效率。为探讨红鳍东方鲀伪雌鱼卵巢发育迟滞的调控机制,本研究从孵化后20日龄开始,用10 μg/L 17 β-雌二醇(E2)浸泡红鳍东方鲀稚幼鱼,每天浸泡1次,每次2 h,至90日龄结束。在90、180和330日龄分别采集处理组(10 μg/L E2)遗传雄性幼鱼和对照组(0 μg/L E2)遗传雌性幼鱼,比较两组幼鱼性腺的组织学和形态学变化特征、下丘脑-垂体-性腺轴相关激素(FSH、LH、E2和17α, 20βOH-PROG)和基因(fshr、lhr、erα、erβ1、erβ2)及脂质积累相关基因(lpl和vldlr)的变化规律。结果显示: 10 μg/L E2可将遗传雄性幼鱼全部诱导为伪雌鱼,且伪雌鱼直至330日龄未二次反转为间性或者雄性,但其性腺系数、卵母细胞数量及卵黄生成前期的卵母细胞面积均显著小于对照雌鱼。此外, 90日龄伪雌鱼的lhr和pgr的表达量显著高于同期对照雌鱼,而17α, 20β-PROG的含量及fshr的表达量显著低于对照组;180日龄伪雌鱼的vldl表达量显著低于对照组;330日龄伪雌鱼的激素含量及基因表达量没有显著差异。综合分析伪雌鱼性腺发育的形态学、组织学和性腺轴相关激素及基因变化规律可见,足够浓度的外源E2能够诱导并维持伪雌鱼的卵巢特征,但E2浓度过高,一方面可能抑制fshr和vldlr基因的表达,从而影响脂质在卵黄生成早期卵母细胞中的积累,导致红鳍东方鲀伪雌鱼卵母细胞生长迟缓;另一方便,高浓度E2抑制伪雌鱼卵原细胞减数分裂的启动,是导致红鳍东方鲀伪雌鱼卵母细胞数量较少的原因之一。     

MS-222对红鳍东方鲀幼鱼血液生化指标的影响

通过研究MS-222对红鳍东方鲀(Takifugu rubripes)幼鱼血液生化指标的影响,以对其使用安全性及麻醉机理的分析提供依据。分别使用20、40、60mg/L等不同浓度的MS-222麻醉红鳍东方鲀幼鱼,测定麻醉后1/4、4、8、24h和复苏后24h鱼体血糖(GLU),血清中总蛋白(TP)、谷丙转氨酶(ALT)、谷草转氨酶(AST)、总胆红素(T-BIL)、尿素氮(BUN)等血液生化指标和血清溶菌酶(LZM)的活性。结果表明,使用MS-222麻醉对红鳍东方鲀幼鱼的大部分血液生化指标和血清溶菌酶活性均有显著影响,且在高麻醉浓度下,这种影响更加显著。使用MS-222麻醉复苏24h后,红鳍东方鲀幼鱼的大多数血液生化指标和血清溶菌酶活性尚未恢复至麻醉前水平。     

迟钝爱德华氏菌对杂交东方鲀rags基因表达的影响

利用实时荧光定量PCR技术检测冀研一号(菊黄东方鲀♀×红鳍东方鲀♂)稚鱼肝胰脏、脾脏、头肾中重组激活基因rags在腹腔注射迟钝爱德华氏菌后6、12、24、36、48、72h内相对表达量的变化情况。试验结果显示,感染迟钝爱德华氏菌后,肝胰脏中rags基因表达呈下降趋势,相对表达量峰值出现在攻毒后6h。脾脏和头肾中rags基因表达均呈先升后降趋势,但在攻毒后48h出现反弹回升。脾脏中,rags基因相对表达量峰值出现在攻毒后6h;头肾中,rag1基因和rag2基因相对表达量峰值分别出现在攻毒后48h和6h。与对照组相比,腹腔注射迟钝爱德华氏菌能引起冀研一号东方鲀rags基因表达上调,且rag1基因和rag2基因表达趋势基本一致。     

Physiological short-term response to sudden salinity change in the Senegalese sole (Solea senegalensis)

The physiological responses of Senegalese sole to a sudden salinity change were investigated. The fish were first acclimated to an initial salinity of 37.5?ppt for 4?h. Then, one group was subjected to increased salinity (55?ppt) while another group was subjected to decreased salinity (5?ppt). The third group (control group) remained at 37.5?ppt. We measured the oxygen consumption rate, osmoregulatory (plasma osmolality, gill and kidney Na⁺,K⁺-ATPase activities) and stress (plasma cortisol and metabolites) parameters 0.5 and 3?h after transfer. Oxygen consumption at both salinities was higher than for the control at both sampling times. Gill Na⁺,K⁺-ATPase activity was significantly higher for the 55?ppt salinity at 0.5?h. Plasma osmolality decreased in the fish exposed to 5?ppt at the two sampling times but no changes were detected for high salinities. Plasma cortisol levels significantly increased at both salinities, although these values declined in the low-salinity group 3?h after transfer. Plasma glucose at 5?ppt salinity did not vary significantly at 0.5?h but decreased at 3?h, while lactate increased for both treatments at the first sampling time and returned to the control levels at 3?h. Overall, the physiological response of S. senegalensis was immediate and involved a rise in oxygen consumption and plasma cortisol values as well as greater metabolite mobilization at both salinities.     

Response of ATPases in the osmoregulatory tissues of freshwater fish Oreochromis niloticus exposed to copper in increased salinity

An increase in salinity of freshwater can affect the physiology and metal uptake in fish. In the present study, Nile tilapia Oreochromis niloticus were exposed to copper (1.0 mg/l) in increased salinities (2, 4, and 8 ppt) for 0, 1, 3, 7, and 14 days. Following the exposures, the activities of Na⁺/K⁺-ATPase, Mg²⁺-ATPase, and Ca²⁺-ATPase were measured in the gill, kidney, and intestine to evaluate the changes in osmoregulation of fish. Results showed that increases in salinity and Cu exposure of fish significantly altered the ATPase activities depending on the tissue type, salinity increase, and exposure durations. Salinity-alone exposures increased Na⁺/K⁺-ATPase activity and decreased Ca²⁺-ATPase activity. Na⁺/K⁺-ATPase activity decreased following Cu exposure in 2 and 4 ppt salinities, though the activity increased in 8 ppt salinity. Ca²⁺-ATPase activity decreased in the gill and intestine in all salinities, while the activity mostly increased in the kidney. However, there were great variations in Mg²⁺-ATPase activity following exposure to salinity alone and salinity+Cu combination. Cu accumulated in the gill and intestine following 14 days exposure and accumulation was negatively correlated with salinity increase. Data indicated that ATPases were highly sensitive to increases in salinity and Cu and might be a useful biomarker in ecotoxicological studies. However, data from salinity increased freshwaters should carefully be handled to see a clear picture on the effects of metals, as salinity affects both metal speciation and fish osmoregulation.     

Hsp60/10 and sHsp families of heat shock protein genes in rainbow trout (Oncorhynchus mykiss) and their expression under heat stress

Heat shock proteins (Hsps) are highly conserved proteins whose expression can be induced by high temperature and play an important role in a variety of biological processes. However, systematic identification of the Hsp60/10 and small Hsp (sHsp) gene family in rainbow trout has not yet been reported, and there is little available information about its roles in evolution in rainbow trout, a typical economical cold-water fish. In this study, we performed a comprehensive analysis of the rainbow trout Hsp60/10 and sHsp gene family and to investigate their expression profiles. A total of one Hsp60 gene, one Hsp10 gene, and ten sHsp genes were identified. According to RNA-seq analysis of rainbow trout liver and head kidney under heat stress, a total of six out of ten sHsp genes were significantly upregulated in liver and head kidney. Real-time RT-PCR (RT-qPCR) was used to quantitatively analyze the expression levels of these genes in different tissues of rainbow trout. Results showed that the expression of hspe1 and hspd1 was lowest in liver and gill, respectively, and highest in brain. In sHsp gene family, all genes are highly expressed in the liver and head kidney, but relatively low in the heart, spleen, brain, gills, and muscles. This systematic analysis provided valuable information about the diverse roles of Hsp60/10 and sHsp in the evolution of teleost fish, which will contribute to the functional characterization of Hsp60/10 and sHsp genes in further research.

     

盐度对点篮子鱼的存活、生长及抗氧化防御系统的影响

在容积为500 L的圆锥形塑料缸中分别用对照(自然海水)、配制的盐度为20、10、5的海水和淡水(地下水)养殖点篮子鱼［(67.76?26.12) g］,研究了不同盐度对点篮子鱼存活、生长和抗氧化酶活性的影响。结果显示,淡水组第9天出现死亡,至第27天时死亡率达100%,其余各组未出现异常,死亡率为0%。各盐度组鱼的特定生长率未表现出显著性差异,但盐度10组鱼体重显著高于盐度20和盐度5组,与对照组无显著性差异；盐度5组全长显著低于其余各盐度组。驯化40 d后,对各组鱼鳃、肝脏、肾脏和肌肉中超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、抗超氧阴离子自由基、羟自由基活性检测结果显示,除盐度5组外,盐度10、20组点篮子鱼鳃、肝脏、肾脏、肌肉中SOD、CAT、抗超氧阴离子自由基和羟自由基活性在驯化40 d后均恢复到对照组水平,组间无显著性差异；盐度5组中鱼鳃的SOD和抗超氧阴离子自由基活性显著高于盐度10和盐度20组,肝脏、肌肉和肾脏中SOD、CAT、抗超氧阴离子自由基和羟自由基活性均恢复到对照组水平。点篮子鱼不同组织中SOD和CAT酶活力在不同盐度下均以肝脏中最高,肾脏和鳃次之,肌肉中最低；抗超氧阴离子自由基活力以肝脏中最高,极显著高于其余各组织中抗超氧阴离子自由基活力(P<0.01),肌肉次之,肾脏和鳃最低；羟自由基活力以肾脏中最高,显著高于其余各组织中羟自由基活力(P<0.05)；鳃次之,肝脏和肌肉中最低,结果表明盐度能影响抗氧化酶活力大小,但并未影响鱼体内酶的分布。     

Effects of experimental hypo- and hyperthyroidism on iodothyronine deiodinases in Nile tilapia, Oreochromis niloticus

In the present study, we examined the effects of experimentally-induced increases or decreases in plasma concentrations of thyroid hormones on iodothyronine deiodinases in tilapia, Oreochromis niloticus. To obtain hyperthyroid tilapia, fish were injected with porcine follicle stimulating hormone (pFSH) 36 hours before sampling or fed on demand for 11 days with tilapia pellets containing 12 ppm T3. Tilapias were made hypothyroid by providing them food containing 0.2% methimazole for 11 days. Plasma T4 and T3 and the in vitro deiodinase activity in liver, kidney, brain and gill were measured at the end of the treatment period. Injection with pFSH caused an increase in plasma T4 but had no influence on plasma T3 levels. A small increase in plasma T3 was observed in T3-fed fish. Plasma levels of both T4 and T3 were decreased by methimazole treatment. We observed no changes in kidney type I deiodinase (D1), whereas liver type II deiodinase (D2) was increased during hypothyroidism and decreased during hyperthyroidism. Hypothyroidism resulted in a significant decrease in brain, gill and liver type III deiodinase (D3). An pFSH-induced increase in T4 stimulated brain and gill D3 but not liver D3, whereas the opposite was true in T3-fed fish. We conclude that the regulation of D1 and D3 in tilapia is probably different compared to mammals.     

低盐胁迫下松江鲈ATP1A3和ATP2B1基因的表达变化规律

为了探究Na+/K+-ATP酶和Ca2+-ATP酶在松江鲈(Trachidermus fasciatus)应对低盐胁迫过程中的调节作用,本研究基于前期转录组数据,获取目标基因ATP1A3 (Na+/K+-ATP酶α3亚基基因)和ATP2B1 (Ca2+-ATP酶1基因)的序列信息并进行了系统进化分析。利用实时荧光定量PCR技术检测了松江鲈的鳃、肠、肾脏和肝脏组织中2个基因在2种低盐胁迫处理(盐度渐变处理,盐度变化速率为1.1/h;盐度骤变处理,盐度变化速率为27/h)下,不同时间点(0 h、12 h、24 h和48 h)的表达水平。系统进化分析结果表明,ATP1A3和ATP2B1基因分别聚类形成独立分支;在各基因分支中,松江鲈与已报道的鲈形目和鲽形目等鱼类共同聚在硬骨鱼类分支中。在2种低盐胁迫处理下,2个基因在鳃、肠、肾脏和肝脏组织中的表达量呈现不同的变化趋势。鳃组织中ATP1A3表达量在盐度渐变处理下先上升后下降,ATP2B1表达量仅在24 h显著升高;盐度骤变处理下,ATP1A3表达量显著下降,ATP2B1表达量显著上升。2种盐度渐变处理下,肠组织中ATP1A3表达量均在24 h显著下降;ATP2B1表达量在盐度渐变处理下显著上升,盐度骤变处理下在24 h显著上升。在盐度渐变处理下,肾脏组织中2个基因的表达量均在24 h显著上升至最大值;ATP1A3表达量在盐度骤变处理下显著上升,ATP2B1表达量在12 h和48 h显著上升。肝脏组织中2个基因的表达量在盐度渐变处理下均无显著变化;盐度骤变处理下,ATP1A3表达量持续显著上升,ATP2B1表达量在48 h显著上升。结果表明,低盐胁迫处理显著影响了ATP1A3和ATP2B1基因的表达水平,但2个基因的表达量变化规律存在显著性差异。上述结果为探讨Na+/K+-ATP酶和Ca2+-ATP酶在鱼类渗透压调节过程中的作用及洄游性鱼类适应盐度变化的分子调控机制提供了理论依据。     

Enhancement of Hsp70 synthesis protects common carp, Cyprinus carpio L., against lethal ammonia toxicity

Exposure to TEX‐OE^®, a patented extract of the prickly pear cactus (Opuntia ficus indica) containing chaperone‐stimulating factor, was shown to protect common carp, Cyprinus carpio L., fingerlings against acute ammonia stress. Survival was enhanced twofold from 50% to 95% after exposure to 5.92 mg L^?1 NH₃, a level determined in the ammonia challenge bioassay as the 1‐h LD50 concentration for this species. Survival of TEX‐OE^®‐pre‐exposed fish was enhanced by 20% over non‐exposed controls during lethal ammonia challenge (14.21 mg L^?1 NH₃). Increase in the levels of gill and muscle Hsp70 was evident in TEX‐OE^®‐pre‐exposed fish but not in the unexposed controls, indicating that application of TEX‐OE^® accelerated carp endogenous Hsp70 synthesis during ammonia perturbation. Protection against ammonia was correlated with Hsp70 accretion.     

Effects of low environmental salinity on the cellular profiles and expression of Na+, K+-ATPase and Na+, K+, 2Cl? cotransporter 1 of branchial mitochondrion-rich cells in the juvenile marine fish Monodactylus argenteus

The goal of this study was to determine the osmoregulatory ability of a juvenile marine fish, silver moony (Monodactylus argenteus), for the purpose of developing a new experimental species for ecophysiological research. In this study, M. argenteus was acclimated to freshwater (FW), brackish water (BW), or seawater (SW). The salinity tolerance of this euryhaline species was effective, and the fish survived well upon osmotic challenges. The largest apical surface of mitochondrion-rich cells was found in the FW individuals. Immunohistochemical staining revealed that Na(+), K(+)-ATPase immunoreactive (NKA-IR) cells were distributed in the interlamellar region of the gill filaments of the silver moony in all experimental groups. In addition to the filaments, NKA-IR cells were also found in the lamellae of the FW individuals. The number of NKA-IR cells in the gills of the FW individuals exceeded that of the BW and SW individuals. The NKA-IR cells of FW and SW individuals exhibited bigger size than that of BW fish. The NKA activities and protein expression of the NKA α-subunit in the gills of the FW individuals were significantly higher than in the BW and SW groups. Additionally, the relative amounts of Na(+), K(+), 2Cl(-) cotransporter 1 (NKCC1) were salinity-dependent in the gills. Immunofluorescent signals of NKCC1 were localized to the basolateral membrane of NKA-IR cells in all groups. In the gills of the FW individuals, however, some NKA-IR cells did not exhibit a basolateral NKCC1 signal. In conclusion, the present study illustrated the osmoregulatory mechanisms of this easy- and economic-to-rear marine teleost with euryhaline capacity and proved the silver moony to be a good experimental animal.     

Effects of Low Salinities on Oxygen Consumption of Selected Euryhaline and Stenohaline Freshwater Fish

The amount of energy required for osmoregulation depends on the difference between internal and external concentrations of ions (Rao 1968; Farmer and Beamish 1969), changes in corticosteroid hormone levels (Morgan and Iwama 1996), glomerular filtration rates (Furspan et al. 1984), gill and kidney Na⁺, K⁺-ATPase activity (McCormick et al. 1989; Morgan and Iwama 1998), tissue permeability to water and ions, and gill ventilation, perfusion, and functional surface area (Rankin and Bolis 1984). Differences in the energetic cost of osmoregulation play a significant role in the difference in growth rate between seawater-and freshwater-adapted fish (Morgan and Iwama 1991; Ron et al. 1995; Wang et al. 1997). Oxygen consumption is an indirect indicator of metabolic rate in fish (Cech 1990) and can be used to determine effects of salinity changes on energy costs.