长江口近海秋季鱼类资源的年变化分析

选用2002~2005年秋季长江口近海渔业资源和温盐度同步调查数据,对该水域秋季鱼类资源量指数、多样性指数、优势种组成以及水温、盐度的年间变化进行了分析,并对鱼类资源量与水温、盐度之间的关系进行了初步研究。结果表明:秋季长江口近海的鱼类资源量指数和多样性指数的年间变化均较为明显,但优势种组成较为稳定,以带鱼、小黄鱼、银鲳、刺鲳为主要优势种,且各年份基本上以带鱼和小黄鱼占有绝对的优势地位。当前长江口近海鱼类群落处于较低水平的相对稳定状态。秋季长江口近海鱼类的资源量和底层水温的变化趋势较为一致,而与表层水温的变化趋势呈现相反的趋势,同时和表底层的水温差变化呈负相关关系;鱼类资源量的变化受表层盐度的影响较为明显,它们之间呈现相同的变化趋势。     

长江口鱼类群落分类学多样性变动的分析

为研究长江口鱼类群落分类学多样性值（平均分类差异指数△+与分类变异差异指数∧+）的长期变动,根据1985~1986年、2004年及2010~2011年3个时期共12个航次长江口鱼类调查资料,分别计算了反映鱼类群落不同物种亲缘关系△+和亲缘关系均匀性∧+值。结果显示,2004年4个航次及2010~2011年3个航次鱼类△+均位于长江口鱼类群落总名录△+95%置信区间以下,与1985~1986年相比,2004年及2010~2011年各航次平均△+均较低;∧+的分布格局则与△+有所不同,主要表现为12个航次的∧+均在95%置信区间内。长江口鱼类群落△+的降低跟过度捕捞、环境污染、生境破坏等有关,其下降也反映出群落种类组成在形态亲缘关系上更加接近。     

长江口海上风电场水域鱼类群落结构特征及其与环境因子的关系

为探明长江口海上风电场水域的鱼类群落结构及其影响因素, 本研究利用多元统计和冗余分析(RDA)等方法对该水域鱼类群落组成及其与环境因子的关系进行分析。春、秋季共获得鱼类 28 种, 隶属 6 目 15 科 26 属; 鲈形目鱼类占比最高(57.14%), 其中以虾虎鱼科鱼类最多(21.43%)。鱼类组成以海洋性、暖温性、底层鱼类为主。春季优势种为棘头梅童鱼 (Collichthys lucidus) 、刀鲚 (Coilia nasus) 、凤鲚 (Coilia mystus) 、拉氏狼牙虾虎鱼 (Odontamblyopus lacepedii)和鮸(Miichthys miiuy), 秋季优势种为龙头鱼(Harpadon nehereus)、凤鲚、棘头梅童鱼、 刀鲚和鮸。多样性分析和 ABC 曲线表明, 调查水域鱼类群落结构处于受干扰状态。T 检验显示, 风电场水域鱼类的丰度、生物量、丰富度指数(D)、均匀度指数(J'')和多样性指数(H'')均与邻近水域无显著性差异(P＞0.05)。等级聚类和非度量多维排序(NMDS)表明, 长江口海上风电场及邻近水域鱼类群落分为春季和秋季 2 个组群。相似性检验 (ANOSIM)显示 2 个组群差异极显著(R=0.726, P＜0.01), 群落结构的季节更替明显。RDA 表明鱼类群落结构受溶氧、 温度、深度和盐度的综合影响, 不同环境因子对不同生活史阶段优势种的影响作用不同。结果表明, 长江口海上风电场及邻近水域鱼类群落结构的干扰状态主要与季节和环境因素相关, 风电场对其影响有限。     

2015年夏季长江口及其邻近海域渔业生物群落结构分析

根据2015年6月(夏季)长江口及其邻近海域的底拖网调查数据,分析了该海域渔业生物种类组成、优势种、群落结构及其多样性特征。结果表明,调查共捕获渔业生物93种,其中底层鱼类56种、中上层鱼类7种、头足类10种和甲壳类20种,以底层鱼类和甲壳类为主。优势种包括小黄鱼(Larimichthy-spolyactis)、鳀(Engraulis japonicus)和带鱼(Trichiurus haumela)。鱼山渔场及舟山渔场近岸区和长江口渔场离岸区群落多样性较高,舟山渔场离岸区和大沙渔场南部多样性较低。渔业生物群落可分为3组:20 m等深线附近的近岸区、20~50 m水深的长江口渔场外部和大沙渔场南部、以及50~75 m水深的舟山渔场和鱼山渔场中外部。渔业生物群落结构不同组间差异主要由小黄鱼、鳀、带鱼和刺鲳(Psenopsis anomala)引起。     

鄱阳湖湖口鱼类资源现状调查

2014年5月-12月对鄱阳湖湖口县水域鱼类资源进行逐月调查,对该水域鱼类种类组成、渔获物结构、优势种、群落多样性指数和单位捕捞努力量渔获量(CPUE)进行分析。结果显示,在鄱阳湖湖口水域共采集鱼类52种,隶属于7目12科40属;优势种分别为鲤(Cyprinus carpio)、鲢(Hypophthalmichthys molitrix)、鲫(Carassius auratus)、鳙(Aristichys nobilis)和光泽黄颡鱼(Pelteobagrus nitidus),占样本个体总数的61.34%;Shannon-Wiener多样性指数(Hi)为2.59,Margalef种类丰富度指数(D)为6.09,Pielou均匀度指数(J')为0.65,Simpson优势度指数(λ)为0.87,相对稀有种数(R)为97.87%;该水域定置网CPUE为1.10~6.21 kg/d,与湖口水位呈显著正相关(P0.05)。鄱阳湖湖口水域渔业捕捞个体以小型鱼类居多,洄游型鱼类的幼鱼补充群体数量极少,鱼类群落多样性指数有上升趋势。     

钱塘江富阳段鱼类资源现状

2014年11月—2015年12月对钱塘江富阳江段3个断面鱼类资源进行了逐月采样调查,对该水域鱼类种类组成、优势种、群落多样性指数和捕捞量进行分析。结果显示:共采集鱼类48种,隶属8目13科37属,其中鲤科鱼类种类最多,占总种类数的64.58%,优势种为鲢、鲤、鲫和光泽黄颡鱼。各月中,4月份捕获的鱼类种数最多,占总种数的52.08%;9月份鱼类捕获量最高,占总渔获量的17.85%。Margalef丰富度指数4月份较高,2月份较低;Shannon-Wiener多样性指数和Pielou均匀度指数在7月份较高,9月份较低,而Simpson多样性指数与之相反。富阳段鱼类捕捞强度较大,渔获物中小个体鱼类占主要部分。与历史记录比较,富阳江段鱼类群落组成已经发生了显著变化,除本地种光泽黄颡鱼外,增殖放流鱼种已成为了优势或重要种群。     

钱塘江水系兰溪段鱼类资源现状

2016年3月—2017年11月,对钱塘江水系兰溪段的鱼类资源进行逐季度采样调查,对该水域鱼类种类组成、生态类型、优势种、多样性指数、群落结构、ABC曲线和捕获情况进行了分析。试验结果显示,共采集鱼类59种,隶属5目13科44属,其中,鲤科鱼类种类最多(67.8%);优势种为鲤鱼和似鳊;生态类型以中小型、杂食性、底层性鱼类为主;Margalef丰富度指数呈先增后减的趋势,2016年的Simpson多样性指数、Shannon-Wiener多样性指数和Pielou均匀度指数均呈逐渐减小的趋势,而2017年这3个指数除9月份最小外,其他月份变化差异不显著;鱼类群落结构季节变化差异显著,但处于稳定状态;鱼类资源严重小型化。     

长江口青草沙水库正式供水前的鱼类群落结构特征

为研究上海青草沙水库的鱼类物种组成、多样性及其空间变化,2010年7--10月在该水库共捕获鱼类993尾,隶属5目,18种,其中淡水鲤形目鱼类最多,占总物种数的72.2％.群落优势种为贝氏(鳖)、刀鲚、鲫、光泽黄颡鱼.聚类分析表明,鱼类群落类型存在较显著的空间差异,刺网网目大小对渔获物物种组成有较显著的影响.物种多样性与丰富度和均匀度均显著正相关,但更多地受丰富度的影响.单因素方差分析表明,鱼类物种多样性在空间上无显著差异.4种摄食功能群中,无脊椎动物食性(44.4％)和杂食性(33.3％)鱼类物种数比例较高;4种生态类群中,定居性鱼类占绝对优势(77.8％).青草沙水库鱼类群落表现出淡水或长江口低盐淡水区鱼类区系的主要特征,与以近海鲈形目鱼类为优势的长江口邻近水域的鱼类群落差异巨大,推测水库建设导致的隔离与盐度下降是形成该水库鱼类群落趋于淡水区系的主要原因.     

长江口及其邻近海域渔业资源结构的季节变化

基于2012年8月(夏季)和11月(秋季)、2013年1月(冬季)和5月(春季)长江口及其邻近海域的渔业底拖网调查数据,对渔业种类组成、数量分布、群落多样性及其与环境因子的关系进行了研究。结果显示,共捕获渔业种类114种,隶属于17目66科90属,其中鱼类12目36科50属58种,鲈形目种类最多(26种),甲壳类2目25科33属49种,头足类仅3目5科6属7种。长江口及其邻近海域渔业资源优势种季节更替明显,仅龙头鱼(Harpodon nehereus)为全年优势种。秋季平均单位网次渔获量最高(29.20 kg/h·net),春季(17.95 kg/h·net)高于夏季(14.60 kg/h·net),冬季最低(10.15 kg/h·net),各季节均以底层鱼类和甲壳类为主,中上层鱼类渔获量仅春季较高,占总渔获量20.1%。春、夏季群落多样性指数较秋、冬季高,春季(163)和夏季(176)渔业资源群落更替指数较高,群落稳定性较低,夏季(6)和冬季(–5)迁移指数接近于零,渔业生物迁入和迁出处于相对平衡状态。各季节渔获种类数和总渔获量分别与底层鱼类和甲壳类渔获量呈极显著正相关;秋季渔获种类数与表层温度呈显著正相关,与深度呈极显著正相关。长江口及其邻近海域渔业低质种类呈增加趋势,并且渔业资源结构存在明显的季节变化,渔获种类数、总渔获量及群落多样性指数与表层温度及深度关系密切。     

长江口及邻近海域无脊椎动物群落结构及其生物多样性研究

根据2006年6月、8月和10月长江口及邻近海域无脊椎动物的底拖网定点捕捞调查资料,研究区域内无脊椎动物的群落结构及其生物多样性.调查共捕获无脊椎动物49种,共2232.277kg、1 037 641尾.分析了调查区域内虾类、蟹类、头足类及口虾蛄4个类别的生物量及密度组成,虾类在密度组成中占主导地位,占总密度的90.1%,蟹类在生物量组成中占主导地位,占总生物量的58.2%.运用相对重要性指数(IRI)研究不同种类的生态优势度,细点圆趾蟹(1 822.64)为6月份的唯一优势种,双斑蝠(1 573.90)及中华管鞭虾(1 135.36)为8月份优势种.三疣梭子蟹(3 667.30)、鹰爪虾(1 568.35)及口虾蛄(1248.70)为10月份优势种.使用多样性指数D、H'、J分析了该水域无脊椎动物群落的多样性,发现在3个航次调查中,10月份多样性指数最高;在不同调查区域,长江口中部多样性指数最高.采用Bray-Curtis指数Cn比较了长江口不同区域的无脊椎动物群落之间物种组成的相似性.结果表明,长江口中部及长江口南部种类组成相似性最高,Cn=0.628;长江口北部和长江口南部种类组成相似性最低,Cn=0.1660与历史资料对比,长江口及邻近海域无脊椎动物主要捕获种类变化不大,群落结构比较稳定.     

Association between the interannual variation in the oceanic environment and catch rates of bigeye tuna (Thunnus obesus) in the Atlantic Ocean

The environmental processes associated with variability in the catch rates of bigeye tuna in the Atlantic Ocean are largely unexplored. This study used generalized additive models (GAMs) fitted to Taiwanese longline fishery data from 1990 to 2009 and investigated the association between environmental variables and catch rates to identify the processes influencing bigeye tuna distribution in the Atlantic Ocean. The present findings reveal that the year (temporal factor), latitude and longitude (spatial factors), and major regular longline target species of albacore catches are significant for the standardization of bigeye tuna catch rates in the Atlantic Ocean. The standardized catch rates and distribution of bigeye tuna were found to be related to environmental and climatic variation. The model selection processes showed that the selected GAMs explained 70% of the cumulative deviance in the entire Atlantic Ocean. Regarding environmental factors, the depth of the 20 degree isotherm (D20) substantially contributed to the explained deviance; other important factors were sea surface temperature (SST) and sea surface height deviation (SSHD). The potential fishing grounds were observed with SSTs of 22–28°C, a D20 shallower than 150 m and negative SSHDs in the Atlantic Ocean. The higher predicted catch rates were increased in the positive northern tropical Atlantic and negative North Atlantic Oscillation events with a higher SST and shallow D20, suggesting that climatic oscillations affect the population abundance and distribution of bigeye tuna.     

Growth performance,digestive enzyme activity and immune response of Japanese sea bass,Lateolabrax japonicus fed with fructooligosaccharide

In this experiment, a feeding trial was performed to determine the effects of fructooligosaccharide (FOS) on growth performance, digestive enzyme activity and immune response of Japanese sea bass, Lateolabrax japonicus juveniles (initial weight 38.3 ± 0.5 g), and the fish were examined following feeding with six levels of FOS (0, 0.5, 1, 2, 4 and 6 g/kg) for 28 days. Significant enhancement of weight gain (WG) and specific growth rate (SGR) was found in fish fed 1 g/kg FOS incorporated diets (p < .05), while the feed conversion ratio (FCR) in the 1, 2 g/kg FOS groups reduced significantly compared with the control (p < .05). Besides, the crude lipid in the 4, 6 g/kg FOS groups increased significantly compared with the control (p < .05). On the other hand, the erepsin and lipase activities significantly elevated in intestine of fish fed 2 g/kg FOS (p < .05) and the lysozyme activity in serum of fish fed 2 g/kg FOS were significantly higher than that in the control (p < .05). Moreover, the alkaline phosphatase activities in serum of fish fed 0.5, 1, 2 g/kg FOS were significantly higher than in control (p < .05). Regression analysis showed that the relationships between dietary FOS levels and either SGR, FCR, erepsin or lysozyme activities were best expressed by regression equations, and the optimal inclusion levels are 1.37, 1.80, 3.06, 3.11, 1.93 and 1.80 g/kg for SGR, FCR, erepsin, lipase, lysozyme and total superoxide dismutase activities, respectively. Overall, this study revealed that FOS incorporated diets could beneficial for L. japonicus culture in terms of increasing the growth, digestion and immune activities. Under the present experimental condition, the optimal supplementary level of FOS in the diet of L. japonicus is 1–3 g/kg.     

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).     

Involvement of gonadal steroids in final oocyte maturation of white perch (Morone americana) and white bass (M. chrysops): in vivo and in vitro studies

Plasma estradiol-17 (E₂), testosterone (T), 17,20-dihydroxy-4-pregnen-3-one (DHP) and 17,20,21-tri-hydroxy-4-pregnen-3-one (20-S) levels were measured by radioimmunoassay (RIA) in white perch (Morone americana) and white bass (M. chrysops) that were induced to undergo final oocyte maturation (FOM) with human chorionic gonadotropin (hCG). Plasma DHP levels increased in females of both species in association with oocyte germinal vesicle migration (GVM) and germinal vesicle breakdown (GVBD) and decreased thereafter. Plasma 20-S levels also increased with oocyte GVM in white bass, but were several-fold lower than DHP levels. Circulating E₂ and T levels were greatest during GVM and GVBD in both species and decreased to low levels during oocyte hydration and ovulation. Follicles from white perch and white bass which received a priming injection of hCG in vivo, produced both DHP and 20-S in vitro after exposure to hCG and their oocytes underwent GVBD. Ovarian incubates from unprimed fish of either species produced only E₂ and T and their oocytes did not complete GVBD. Oocytes from unprimed bass, but not perch, matured when follicles were exposed to hCG in vitro. Both trilostane and cycloheximide blocked in vitro production of DHP and 20-S and oocyte GVBD by white perch follices. DHP and 20-S were equipotent inducers of FOM in the GVBD bioassay. None of several other structurally-related steroids tested were effective within a physiological range of concentrations. These results indicate a role for DHP and 20-S in the control of FOM in white perch and white bass.     

Cardiac,ventilatory and metabolic responses of two ecologically dissimilar species of fish to waterborne cyanide

Changes in heart rate, ventilatory activity and oxygen consumption were determined in trout (Salmo gairdneri) and brown bullhead catfish (Ictalurus nebulosus) during exposure to a steadily increasing concentration of waterborne cyanide selected to produce death in 8–9 hours for each species. The lethal cyanide concentration for the bullheads was an order of magnitude higher than for trout. Trout developed an immediate and gradually increasing bradycardia throughout the exposure period. Cyanide produced tachycardia in the bullhead followed by a gradual onset of bradycardia as the concentration of cyanide was raised. Pericardial injection of atropine (a muscarinic cholinergic antagonist) indicated that bradycardia in the trout was due initially to increased vagal tone but later due to the direct effect of cyanide on the heart. Hyperventilation in the trout persisted throughout the exposure period, although the rate and amplitude fluctuated and was variable between individual fish. During the last hour of exposure (highest cyanide concentration), ventilation was characterized by rapid, shallow breaths followed by a sudden respiratory arrest. The bullheads exhibited hyperventilation during the first 3 hours of exposure followed by a gradual, linear drop in ventilation rate and amplitude until death occurred. Cardiac and ventilatory responses in both species were attributed to stimulation of central and peripheral chemoreceptors by cyanide. Evidence is presented which suggests the initial response in the bullheads was due, at least in part, to gustatory stimulation by the cyanide. Oxygen consumption of the trout remained above pre-exposure levels for the majority of the test period. Oxygen consumption in the bullhead paralleled the changes in heart and ventilatory rates. Whole-body lactate levels of fingerlings of both species during cyanide exposure were measured to estimate the extent of anaerobiosis. Whole-body lactate levels were much greater in the bullheads than the trout, indicating a higher capacity for anaerobiosis, possibly due to a greater fuel supply. Overall, the trout responded to cyanide in a manner similar to that produced by environmental hypoxia whereas the bullheads experienced a gustatory stimulus which masked the hypoxia-like response.     

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.