碳酸盐碱度对青海湖裸鲤幼鱼肝和肾SOD、ACP和AKP酶活性的影响

青海湖裸鲤(Gymnocypris przewalskii, 以下简称裸鲤)为耐盐碱鱼类。自青海湖裸鲤救护中心取裸鲤幼鱼, 全长(4.42±0.02) cm, 体质量(0.84±0.01) g。碳酸盐碱度暴露浓度设定为 32 mmol/L(C_A32)和64 mmol/L(C_A64), 通过测定青海湖裸鲤幼鱼肝和肾中超氧化物歧化酶(SOD)、酸性磷酸酶(ACP)和碱性磷酸酶(AKP)酶活性变化规律, 探索裸鲤幼鱼肝和肾中SOD、ACP和AKP对碳酸盐碱度胁迫的生理响应。在本试验范围内, 裸鲤在高碱环境中显示出较强的适应调节能力, 在碳酸盐碱度胁迫下, SOD、ACP和AKP酶活性均能在发生显著变化后快速恢复到初始水平, 但3种酶显示出不同的变化规律: (1)肝SOD在C_A32和C_A64胁迫3 d、肾SOD在C_A32胁迫4 d、C_A64胁迫3 d时, 酶活性均显著升高。(2)肝和肾ACP活性出现不同的变化趋势, 肝ACP活性仅在C_A64胁迫组4 d出现显著上升, 而肾ACP活性在C_A32胁迫0.5 d、7 d和C_A64胁迫1 d时分别出现了显著性波动。(3)肝AKP在C_A32胁迫1 d、C_A64胁迫3 d时, 酶活性显著升高, 而肾AKP仅在C_A32胁迫0.5 d时, 酶活性显著升高。在碳酸盐碱度胁迫下, 3种酶活性均能发生显著变化, 说明青海湖裸鲤幼鱼通过抗氧化及去磷酸化应激调节, 来更好地应对高碱环境。

     

三角帆蚌内脏团不同部位插核育珠对珍珠囊形成的影响

对三角帆蚌(Hyriopsis comingii)内脏团不同部位进行插核, 研究各组珍珠囊形成、结构以及珍珠质沉积的差异, 从而确定出有利于珍珠形成的插核核位。实验选取内脏团5个部位(I: 斧足内脏团前端; II: 斧足内脏团中部; III: 近生殖腺部; IV: 近胃部; V: 近肾部)进行插核, 并分别在插核后第20、50、90、150 天(thd)采集内脏团插核部位进行组织固定, 利用石蜡切片、HE染色研究不同插核部位珍珠囊结构及珍珠质沉积情况。结果表明: (1) 插核施术后20 d, II组插核位点最早形成单层低柱状上皮细胞, 为次生珍珠囊; (2) 插核施术后50 d, I、II、III组均形成了珍珠囊上皮细胞, 而IV、V组插核位点未出现类似的柱状细胞。其中II、III组珍珠囊上皮细胞前端含有大量体积较大的颗粒物; (3) 插核施术后90 d, I、III组珍珠囊细胞间出现大量细胞间隙, I、II组珍珠囊表皮细胞具有多核现象的细胞数量增多, 且II、III组上皮细胞中颗粒物数量增多, 而IV、V组插核位点形成了复层扁平上皮细胞; (4) 插核施术后150 d, I、III组珍珠囊内表皮细胞间隙变少。II组珍珠囊上皮细胞游离端存在大量的微绒毛, 其与III组相似, 珍珠囊上皮细胞细胞核明显增多, 颗粒物减少。该时期, IV组在插核位点上形成了不连续的低柱细胞、V组插核位点仍未出现珍珠囊细胞。(5) 三角帆蚌在插核术后养殖150 d后, I、II、III组珠核表面出现明显的珍珠质沉积, II、III组珍珠质沉积均匀, I组不均匀, 并且II组沉积的珍珠层厚度(0.85 mm±0.06 mm)显著大于I、III组(P<0.05; 0.62 mm±0.07 mm, 0.56 mm±0.03 mm), 而IV、V组珠核表面没有珍珠质沉积。研究结果表明, 三角帆蚌内脏团不同插核部位珍珠囊上皮细胞的形成存在明显差异, 斧足–内脏团前端、斧足–内脏团中部以及近生殖腺部插核能形成完整的珍珠囊结构并沉积珍珠质, 其中斧足–内脏团中部插核更有利于珍珠的生长。本研究旨为淡水珍珠贝的内脏团育珠研究工作提供实践基础和理论依据。

     

南极大西洋扇区南极磷虾渔获率序列的振荡模态分析

为了解释南极大西洋扇区的48区南极磷虾(Euphausia superba)资源的多尺度振荡模态特征及其与环境振荡之间的响应关系, 采用经验模态分解方法, 对1982-2011年间的南极磷虾月均渔获率进行了分析。结果表明, 其振荡表现出了0.5 a、1 a、1.5 a、2.5 a、7 a和11 a等多个周期, 其中高频振荡对南极磷虾资源变动影响较大, 低频振荡影响较小; 3个亚区渔获率都为冬高夏低季节性振荡, 48.1~48.3亚区最高值依次出现在5月、 6月和9月, 渔获率的最低值出现在1月; 所有振荡周期中以1 a为最主要振荡周期(方差解释率为46.7%), 南极磷虾年补充规模对其渔获率最为重要; 其2.5 a振荡和海冰面积3.0 a;振荡有关; 渔获率低频振荡周期与气候-海流系统振荡周期有关。海冰面积和渔获率有较好的正相关关系(相关系数为0.44, 位相差10个月)。海冰面积异常振荡会在8~11个月之后对渔获率和渔获率异常产生的正相关影响。磷虾资源的振荡是环境振荡和磷虾生物周期综合作用的反映。

     

β-葡聚糖与硒、维生素E联合添加对凡纳滨对虾生长、血清免疫和抗氧化指标及抗病力的影响

选取800尾初始体质量为(0.83±0.02) g的凡纳滨对虾(Litopenaeus vannamei), 随机分成5组, 分别投喂添加β-葡聚糖(βG)、硒(Se)和维生素E(VE)的饲料, 其组合和添加量分别为: 0、300 mg/kg βG、300 mg/kg βG+0.2 mg/kg Se、300 mg/kg βG+100 mg/kg VE、300 mg/kg βG+0.2 mg/kg Se+100 mg/kg VE, 记为G0、G1、G2、G3和G4, 养殖35 d, 养殖结束后, 采用肌肉注射法对凡纳滨对虾进行白斑综合征病毒(WSSV)感染。结果显示, 养殖结束时G2组对虾增重率最高, 比G1组提高6.4%; 饵料系数比G1组降低6.3%, 显著低于G1组(P<0.05); G3组对虾存活率显著低于G0和G1组(P<0.05)。与G0组相比, G4组对虾血细胞总数和血清酚氧化酶活性显著升高(P<0.05); 与G1组相比, G2−G4组血细胞总数和酚氧化酶活性差异不显著(P>0.05), 但溶菌酶活性显著升高(P<0.05)。G3组酸性磷酸酶活性显著低于G4组(P<0.05); G2组碱性磷酸酶活性显著高于其他各添加组(P<0.05), 而与G0组差异不显著(P>0.05)。G4组谷胱甘肽过氧化物酶活性显著高于其他4组(P<0.05); 谷胱甘肽转移酶活性在各组间差异不显著(P>0.05)。G1组过氧化氢酶活性显著高于G2和G4组(P<0.05)。超氧化物歧化酶活性以G2组最高, 显著高于其他各组(P<0.05); G1和G3组次之, 分别显著高于G0和G4组(P<0.05)。G1、G2和G4组血清丙二醛含量较低, 分别显著低于G0和G3组(P<0.05); 抗超氧阴离子活性较高, 分别显著高于G3组(P<0.05)。与G1组相比, G3组总抗氧化能力显著升高(P<0.05)。注射WSSV粗提液72 h时, 对虾的累积死亡率以G0组最高, G1−G4的累积死亡率呈现降低的趋势, 其中G2和G4组显著降低(P<0.05), 其相对保护率分别为30.8%和26.9%。结果表明, βG与Se联合添加能一定程度提高凡纳滨对虾生长性能, 降低饵料系数; 与单独添加βG相比较, βG与Se联合添加或βG与Se、VE三者联合添加均能显著提高凡纳滨对虾的非特异性免疫、抗氧化能力和抗病力。

     

合浦珠母贝幼贝生长性状的遗传参数估计

以广东徐闻和海南三亚2个地理群体合浦珠母贝(Pinctada fucata)为亲本, 采用人工授精方法构建了33个全同胞家系。在162日龄时从每个家系随机抽取50个个体, 共1 650个, 测量其壳长、壳高、壳宽和体质量4个生长性状, 利用动物模型对4个性状进行遗传参数分析。结果表明, 合浦珠母贝4个生长性状的总平均值分别为(16.28 ± 4.46) mm、(14.85 ± 4.39) mm、(4.58 ± 1.52) mm、(0.66 ± 0.67) g。4个性状的遗传力分别为0.202 ± 0.020、0.203 ± 0.020、0.200 ± 0.021和0.204 ± 0.020, 均属中等遗传力, 因此可以用选择育种进行遗传改良。4个性状间表型相关系数和遗传相关系数的范围分别为0.667~0.698和0.685~0.959, 其中壳长、壳高和壳宽之间的遗传相关系数均低于0.7, 与表型相关一致, 而三者与体重间的遗传相关系数较高(0.868~0.959), 其中壳宽与体质量间的遗传相关系数最高(0.959)。本研究中合浦珠母贝的4个性状为中等遗传力, 并可通过对壳宽的选育来改良体质量性状。上述结果为进一步开展合浦珠母贝选择育种研究奠定了基础。

     

达氏鲟视网膜早期发育及其相关机能

本研究采用石蜡连续切片技术, 对出膜后0~64 d 的达氏鲟(Acipenser dabryanus)视网膜结构、视觉特性及相关机能进行研究。结果显示, 达氏鲟初孵仔鱼的视网膜没有分化, 视单锥细胞在36 h 出现, 视杆细胞在6 d 时出现, 7 d 时视网膜各层分化完毕。最小分辨角由8 d 的13.26′下降到64 d 的3.37′, 仔鱼发育到13 d 时表现出明显的视网膜运动反应。随着仔鱼发育, 视单锥细胞及神经节细胞密度不断降低, 视杆细胞密度不断增加, 外核层细胞核与视锥细胞及神经节细胞数量的比值均不断增大。结果表明6~12 d 是达氏鲟视网膜结构快速发育和视觉特性发生明显变化的时期, 这种变化与其生态变迁、趋光性及摄食方式的变化相适应。本研究旨在探明达氏鲟视网膜的发育特性及其相关机能特点, 为开展规模化繁育与种群资源的保护提供理论依据。

     

脱脂蚕蛹替代日粮中鱼粉对建鲤肠道菌群的影响

利用免培养的16S rDNA梯度凝胶电泳技术(DGGE)研究脱脂蚕蛹替代鱼粉对建鲤(Cyprinus carpio var. jian)肠道菌群的影响。6个饲养组分别饲喂6种等氮等能饲料, 分别为含10%鱼粉的基础饲料、3种替代饲料(脱脂蚕蛹替代鱼粉蛋白, 替代水平分别为25%、50%和75%)及2组分别在50%和75%替代基础上分别再添加0.6%和0.7%晶体赖氨酸的饲料 (分别记为DSP0、DSP25、DSP50、DSP50-Lys、DSP75、DSP75-Lys)。饲养结束后采集肠道样品, 分析建立指纹图谱, DSP0、DSP25、DSP50、DSP50-Lys、DSP75、DSP75-Lys组分别产生了19、15、11、12、8和12条可鉴别条带, 各组均存在优势种群条带。DSP0和其他各组(DSP25、DSP50、DSP50-Lys、DSP75、DSP75-Lys)的相似性指数为50.7%、50.6%、69.0%、42.4%、66.7%。对PCR-DGGE指纹图谱主要条带进一步回收、克隆和测序, 共得到19条序列, 将得到的序列在NCBI数据库中进行同源分析, 发现建鲤肠道菌群归为芽孢杆菌纲、螺旋体纲、β-变形菌纲、梭菌纲、放线菌纲、γ-变形菌纲、蓝藻纲、拟杆菌纲、梭杆菌纲等, 大部分为不可培养细菌。研究发现, 脱脂蚕蛹替代鱼粉对建鲤肠道菌群组成产生显著影响, 随着脱脂蚕蛹替代水平的提高, 肠道菌群多样性下降, 细菌种类从19种锐减至8种, 而饲料中补充赖氨酸可减弱这种影响, 本研究可为蚕蛹在鲤配合饲料中的开发应用提供参考资料。

     

虾夷马粪海胆溶菌酶基因全长cDNA的克隆与表达分析

本实验采用RT-PCR和cDNA末端快速扩增(RACE)技术克隆得到了虾夷马粪海胆(Strongylocentrotus intermedius)溶菌酶(LYZ)基因的全长cDNA序列。结果表明, 虾夷马粪海胆LYZ基因全长为912 bp, 含有1个480 bp的开放阅读框(ORF), 编码159个氨基酸, 其中第1−20个氨基酸为信号肽, 蛋白计算分子量为17.69 kD, 等电点为7.75。氨基酸比对分析表明, 虾夷马粪海胆LYZ基因与紫球海胆(Strongylocentrotus purpuratus)和刺参(Apostichopus japonicus)的i型LYZ基因相似百分比分别为91.4%和59.3%, 并且含有i型LYZ基因的保守序列DVGSLSCGP (Y)Y(F)QIK, 所以推断本实验克隆的溶菌酶为i型。采用实时定量PCR方法, 以β-actin为内标, 对其在虾夷马粪海胆各组织中的表达进行研究, 发现LYZ基因在围口膜中表达量最高, 其次是齿间肌、管足、肠、体腔液、雄性性腺和雌性性腺。利用脂多糖(LPS)刺激虾夷马粪海胆, 取刺激后不同时间的海胆体腔液, 对该基因的表达差异进行分析。结果表明, 虾夷马粪海胆的LYZ基因在LPS刺激后8 h时表达量最高, 12 h时开始逐步回落, 至36 h时回落至对照组相近水平。本结果可为虾夷马粪海胆免疫学研究及抗病相关分子标记的开发提供参考依据。

     

饲料中添加浒苔对黄斑蓝子鱼生长性能与生理生化指标的影响

试验用黄斑蓝子鱼(Siganus canaliculatus)幼鱼捕自汕头大学南澳临海试验站附近海域, 在海上网箱中暂养半个月后将其转入室内水族缸(容积200 L)中驯养2周, 饵料为自制配合饲料。新鲜浒苔(Enteromorpha prolifera)从汕头市南澳县盐田采得, 用水清洗后晒干, 经小型粉碎机粉碎, 过60目筛, 制成海藻干粉。选取体质量约23 g黄斑蓝子鱼进行试验。在蛋白水平32%、脂肪水平8%的情况下, 配制6种配合饲料, 其中3种饲料分别添加5%、10%和15%的浒苔干粉, 另2种添加10%、15% 浒苔的饲料中还添加0.2%非淀粉多糖酶(NSP酶), 对照组饲料不添加浒苔。养殖试验周期为8周。结果显示: 与对照组相比, 5%浒苔组鱼的生长性能不受影响(P>0.05), 但10%和15％浒苔组鱼的生长性能显著降低(P<0.05); 然而, 在添加0.2% NSP酶的情况下, 10％和15%浒苔组鱼的生长性能与对照组相比无显著差异(P>0.05)。各饲料组鱼的成活率及全鱼的水分、蛋白、脂肪、灰分含量无显著差异(P>0.05)。与对照组鱼相比, 浒苔饲料组鱼肝和肌肉中的过氧化氢酶及谷胱甘肽过氧物酶的活性增高, 丙二醛含量降低。结果表明, 黄斑蓝子鱼配合饲料中浒苔的添加比例可达5%; 在加入一定量NSP酶的情况下, 其添加比例可达10%～15%。饲料中添加适当比例的浒苔可提高鱼体的抗氧化能力。本研究旨在探讨浒苔作为黄斑蓝子鱼配合饲料原料加以利用的可行性, 为浒苔资源开辟一条有效的利用途径, 并为研发高效、低成本蓝子鱼配合饲料提供指导和依据。

     

基于多源数据的东海小黄鱼资源评估与管理

为建立稳定环境和波动环境机制下预防性渔业管理生物参考点, 整合调查设计和渔捞日志等多源资源指标构建混合矩阵, 利用logistic和Fox剩余产量模型的两步分析技术, 对东海区小黄鱼(Larimichthys polyactis)渔业资源动态进行评估。模型估算参数和管理参考点显示, Fox模型对渔获量和CPUE拟合的方差贡献率高于logistic模型, 两者分别为68%和57%, 环境承载力和内禀增长率相差较大。logistic模型估算了相对较低的承载力和较高的内秉增长率、初始开发率以及MSY。稳定环境下资源状况评判结果表明: 1999―2008年间多数年份的捕捞强度超过捕捞水平限制参考点, 渔业遭受过度开发, 平均资源量保持在中位水平且未达到过度捕捞状态, 但已超过目标参考点; 波动环境条件下的判别结果显示: logistic和Fox模型拟合的渔业水平均已达到过度捕捞。采用保护性捕捞参考点可增强渔业资源稳定性, 当捕捞死亡从参考点F_MSY降至预防性参考点F_opt, logistic模型估算资源量从8.1 t上升到10.1 t, 而渔获量从13.1 t下降至12.3 t; Fox模型资源量则从11 t增加到15.9 t, 相应的捕捞产量从12.8 t下降到11.6 t。Fox模型评估结果较为保守, 适合预防性渔业管理。

     

Rare serotype occurrence and PFGE genotypic diversity of Streptococcus agalactiae isolated from tilapia in China

Previously, we reported 10 PEGE types of 85 tilapia Streptococcus agalactiae(GBS), which shifted from Streptococcus iniae in China, by using PEGE method. Presently, larger and more representative tilapia GBS were isolated, for the ?rst time in China, to characterize their serotypes and genetic diversities more precisely than had done before. 168 GBS strains were distributed in ?ve provinces of China, in which Guangdong, Guangxi and Hainan were the major ones, holding36.9%(62/168), 37.5%(63/168) and 19.6%(33/168), respectively. Serotypes, Ia, Ib and III, were observed in these strains and the most predominant one was Ia(95.2%), which mainly distributed in Guangdong, Guangxi and Hainan. Ia initially occurred in 2009, it shoot up to 32.1% in 2010,but decreased to 16.1% in 2011 before went up to 45.2% in 2012. Ib sporadically occurred during2007–2011, III onlyoccurred in 2012. 14 different PFGE types, including 4 new types(N, O,P and Q), were observed, in which B, D, F and G were the predominant types, holding 83.9%(141/168) of the total GBS strains. Ia corresponded to 11 PFGE types(A–H, N–P), in which type D predominated(51%). Ib represented 3 genotypes(I, J and Q) and III harbored only 2genotypes(N and F). Type N and Fsynchronously presented in Ia and III. In summary, the genetic diversity of tilapia GBS varied by serotypes and changed with geographical locations and years.Although Iastillpredominated, new rareserotypeIII alreadyoccurred in China.     

Growth hormone (GH) and reproduction: a review

Interaction between growth and reproduction occurs in many vertebrates and is particularly obvious at certain stages of the life cycle in fish. Endocrine interactions between the gonadotropic axis and the somatotropic axis are described, the potential role of GH being emphasised. A comparative analysis of these phenomena in mammals, amphibians and fish, suggests a specific role of GH in the physiology of puberty, gametogenesis and fertility. It also shows the original contribution made by studies on the fish model in this field of investigations.     

Purification and partial characterization of GtHs (cfLH and cfFSH) from Indian walking catfish (Clarias batrachus) (L.) and development of a homologous ELISA for cfLH

Two gonadotropins (GtH; Qa and Qb) were purified by gel filtration and ion exchange chromatography from the pituitaries of Indian walking catfish (Clarias batrachus). The presence of GtH during purification was assessed by in vitro oocyte maturation and in vivo steroidogenic activity, and their identities were determined by elution profiles, molecular weight, biological activities and yield. The molecular weights of Qa and Qb were 37 and 42 kDa, respectively, and composed of distinct subunits (Qa: 20 and 14 kDa and Qb: 26 and 18 kDa). Polyclonal antibodies raised against Qa immunostained Qa, Qb and pituitary GtH cells. A competitive Qa‐ELISA was developed whose sensitivity was 6.25 ng mL^?1 (1.25 ng well^?1) with intra‐ (3.5%) and inter‐ (12.4%) assay coefficients of variation. Displacement curves parallel to the standard were obtained with plasma and pituitary extracts of catfish, Qb and carp GtHII. The assay was validated by measuring the plasma Qa levels after LHRH treatment and in relation to ovarian growth in the female catfish during different reproductive phases. Based on the results, Qa and Qb corresponded to fish LH and FSH respectively. The findings will increase the knowledge of the mechanisms controlling fish reproduction and identification of sensitive phases in fish in captivity for hormonal manipulation.     

Controlled infection of Poecilia reticulata Peters (guppy) with Tetrahymena by immersion and intraperitoneal injection

Tetrahymena is a protozoan parasite, which infects guppy, Poecilia reticulata Peters, and causes substantial economical losses in commercial farms worldwide. Studies of guppy infected by Tetrahymena require standardized infection protocols. The LD50 for Tetrahymena infection of guppies by intraperitoneal (IP) injection was calibrated, and the level obtained was 946 parasites per fish. Guppy infection with Tetrahymena by immersion, imitating the natural route of infection via the integument, was studied under normal or stress conditions. Exposure to cold and netting (CNI) and to cold only (CI) followed by immersion exposure to 10 000 Tetrahymena per mL resulted in 22.5% and 19.2% mortality, respectively, as compared to 14.2% and 10% in groups that were netted only (NI) or non‐stressed (I). Histopathology revealed that immersion infection resulted in a systemic infection. Lysozyme levels, measured 3 weeks after infection, were significantly higher in the CNI group (288 μg per mg protein) compared with CI‐, NI‐ and I‐treated groups (94.5, 64 and 62.3 μg mg^?1, respectively). There was no evident parasite immobilization activity in body homogenates, suggesting no development of acquired immunity. Re‐infection by IP injection revealed no increase in protection in any of the treatment groups, mortality range of 56.3–75%, higher than in the non‐exposed control (40.6% mortality).     

Evaluation of a Fast Method Based on the Presence of Two Restriction Sites in the Mitochondrial ND5 (mt ND5) Gene for the Identification of Scomber Species

The purpose of this work was to evaluate the suitability of a method based on the presence of two restriction sites (for Hae III and Hindf I) in the mitochondrial NADH dehydrogenase subunit 5 (mt ND5) gene to identify Scomber species. The evaluation was performed on 144 reference and market samples by sequencing of the entire 505-bp fragment of the mt ND5 gene and of a 464-bp fragment of the Kocher fragment of the cytochrome b gene (mt Cytb). Sequence analysis of any of the two fragments allows the identification of each of the four Scomber species, but S. japonicus and S. colias had the same restriction sites at the ND5 amplicon and would not have been differentiated by this analysis. Similarly, loss of the Hae III site in some S. scombrus individuals would have misidentified them as not being Scomber. All the market products were correctly labeled except one acquired in Spain labeled as originating in the Atlantic and containing S. japonicus.     

Imported ornamental fish are colonized with antibiotic‐resistant bacteria

There has been growing concern about the overuse of antibiotics in the ornamental fish industry and its possible effect on the increasing drug resistance in both commensal and pathogenic organisms in these fish. The aim of this study was to carry out an assessment of the diversity of bacteria, including pathogens, in ornamental fish species imported into North America and to assess their antibiotic resistance. Kidney samples were collected from 32 freshwater ornamental fish of various species, which arrived to an importing facility in Portland, Oregon from Colombia, Singapore and Florida. Sixty‐four unique bacterial colonies were isolated and identified by PCR using bacterial 16S primers and DNA sequencing. Multiple isolates were identified as bacteria with potential to cause disease in both fish and humans. The antibiotic resistance profile of each isolate was performed for nine different antibiotics. Among them, cefotaxime (16% resistance among isolates) was the antibiotic associated with more activity, while the least active was tetracycline (77% resistant). Knowing information about the diversity of bacteria in imported ornamental fish, as well as the resistance profiles for the bacteria will be useful in more effectively treating clinical infected fish, and also potential zoonoses in the future.     

Effect of iodophor disinfection of non‐hardened Salmo trutta eggs on their bacterial and fungus load

This study investigated the efficiency of iodophor disinfection (135 ppm active iodine for 15–30 min) of non‐hardened Salmo trutta eggs against different groups of bacteria and against fungus. Egg samples were taken from non‐disinfected and from disinfected eggs, microorganisms were cultured on specific nutrient media and their mass was measured by turbidimetric methods. Bacteria and fungus mass of non‐hardened eggs could be reduced but not eliminated by iodophor disinfection with 135 ppm active iodine for 15 min. The extent of reduction was 47–65% (Experiment 1). The efficiency of disinfection increased with disinfection time as the reduction in bacteria and fungus mass was 40–55% after 15 min and 58–74% after 30 min (Experiment 2). Disinfection efficiency of iodophor solution diluted in water (reduction 49–57%) and of iodophor solution diluted in sodium chloride solution iso‐osmolar to the oocytes (reduction 52–61%) was similar (Experiment 3). The reduction in bacteria and fungus mass was persistent as it was 39–72% lower in embryos deriving from disinfected eggs than in embryos deriving from non‐disinfected ones (Experiment 4). In conclusion, the tested disinfection method is inadequate to eliminate pathogens completely but it could positively influence immune defence of eggs and embryos.     

Nitrogenous waste excretion and accumulation of urea and ammonia inChalcalburnus tarichi (Cyprinidae), endemic to the extremely alkaline Lake Van (Eastern Turkey)

The endemic, anadromous cyprinidChalcalburnus tarichi is the only fish species known to occur in alkaline Lake Van (Eastern Anatolia, Turkey). EightC. tarichi were maintained individually in Lake Van water (17 – 19°C; pH 9.8; 153 mEq·I^–1 total alkalinity; 22 total salinity) and tank water samples analyzed for 24 h in 2 to 4 h intervals. At zero time, < 1µM ammonia was present and urea was undetectable in the tank water; at 24 h, total ammonia and urea made up 114±32 and 35±25µM, respectively. Over the experimental period, ammonia-N and urea-N excretion averaged 1041±494 and 607±169moles·kg^–1 fish·h^–1, respectively. The extent of urea excretion was highly variable between specimens. Uric acid excretion was not detectable.Urea was present at high concentrations in all tissues and plasma (25 – 35moles·g^–1·ml^–1) of freshly caughtC. tarichi; total ammonia content of the tissues was by a factor of 1.9 (liver) to 3.0 (brain) lower. High arginase activity (2.4±0.2 U·min^–1·g^–1) was detected in the liver ofC. tarichi but ornithine carbamoylphosphate transferase, a key enzyme of the ornithine-urea-cycle, was absent. Ureagenesis is likely through degradation of arginine and/or uricolysis. High glutamine synthetase activity (11±0.6 U·min^–1·g^–1) and low ammonia content in brain suggest that, like other teleosts,C. tarichi has an efficient ammonia detoxification in the brain, but in no other tissue.Nitrogenous waste excretion at alkaline pH is discussed. The ability ofC. tarichi to excrete high levels of ammonia at extremely alkaline pH is unique among teleosts studied so far. The mechanism of ammonia excretion under Lake Van conditions remains to be elucidated.