象山港不同温度区围隔浮游生态系统营养盐迁移—转化的模拟对比

为评估象山港海域电厂温排水对水体富营养化影响,以生态系统中氮、磷营养盐循环为主线,建立了适用于海洋围隔浮游生态系统的多变量的营养盐迁移—转化动力学模型。该模型包括浮游植物、浮游动物、溶解无机态营养盐、溶解有机态营养盐和生物碎屑5 个模块,涉及溶解无机氮、磷酸盐、溶解有机氮、溶解有机磷、浮游植物、浮游动物和生物碎屑7 个状态变量。利用2010年10月象山港其中一个温度区的围隔生态实验数据成功地进行了模型的验证,确定了相关参数的量值,并用该参数同时模拟3个不同温度区围隔氮、磷营养盐生物化学迁移—转化过程,进而得出温度对围隔浮游生态系统氮、磷营养盐迁移—转化影响的结论。结果表明,象山港电厂温排水加剧了受纳水体的富营养化程度。     

海水池塘鱼贝施肥混养生态系中贝类与浮游生物的相互影响_

于１９９５年６－９月间在施肥鱼贝混养生态系中，实验研究了搭配养殖菲律宾蛤仔对浮游生物的效应和浮游生物对菲律宾蛤仔养殖的影响。在浮游生物群落构成方面，菲律宾蛤仔使蓝藻、甲藻和浮游桡足类显著减少。对生物量和初级生产力的影响程度与养殖密度有关，而浮游生物丰度和初级生产力在时间上的变化又与营养盐有关。     

基于Ecopath模型的20世纪80年代武汉东湖生态系统结构和能量流动研究

为了解1980s蓝藻水华等环境干扰期间武汉东湖生态系统的结构和特征,依据1980s武汉东湖生态环境及鱼类资源的调查数据构建东湖湖泊生态系统Ecopath模型,定量分析东湖生态系统食物网结构及能量流动特征。该生态系统模型由大型鲌类、其他肉食性鱼类、红鳍原鲌（Chanodichthys erythropterus）、杂食性鱼类、其他小型鱼类、浮游生物食性鱼类、虾类、底栖生物、浮游生物、大型沉水植物和碎屑等14个生物组分构成,基本覆盖整个东湖生态系统食物网。Ecopath模型结果表明,武汉东湖生态系统主要由4个整合营养级构成,鲢（Hypophthalmichthys molitrix）、鳙（Aristichthys nobilis）和浮游植物的营养转换效率很低。系统的香农多样性指数为1.47,说明系统在该时期的组分简单,抵抗能力弱;系统的循环指数为3.541%,远小于10%,说明系统整体的再循环能力低。系统的总初级生产量/总呼吸量（TPP/TR）、连接指数（CI）、Finn’s循环指数（FCI）、Finn’s平均能流路径长度（FML）和系统杂食性指数（SOI）分别为3.802 2、0.331...     

电厂温排水对水生生物影响评价综述

总结温排水对水生生物和生态系统的一般性影响;介绍我国和美国4个不同环境背景的大型电厂温排水对当地水生生物的影响;分析厂址特定因素和环境背景的影响;讨论电厂温排水影响评价存在的问题。(1)温排水可能会影响水生生物的生长、生存和繁殖,改变群落的多样性和丰度,并可能导致栖息地的变化,但影响性质和程度各不相同;(2)温排水对水生生物的潜在影响程度与厂址特定因素包括地理位置、受纳水体是海水还是淡水、受纳水体的体积、水交换速率、生物栖息地等密切相关;(3)为了准确评价温排水的影响,我国首先应根据不同海域、流域或湖泊的特点,选择出代表性重要水生生物并进行热影响研究,为不同流域、湖泊、海域温度基准的制定奠定基础;应尽快制定温排水环境影响评价导则,使得温排水限值能够满足国家水体质量标准,确保受纳水体中平衡土著的贝类、鱼类和野生生物种群的生长和繁育,并且已考虑了温排水与所有其他对物种重要影响(包括杀生剂的影响、取水卷吸效应的影响、过度捕捞、其他污染源的排放等)的累积影响。     

基于Ecopath模型的筑坝河流浮游生物变化分析

了解浮游生物对河流筑坝的响应，为高原河流的生态保护与可持续利用提供科学依据。基于野外调查、历史调研和室内实验，分别构建2007年（筑坝前）和2018年（筑坝后）火烧沟河流水生生态系统的Ecopath模型，通过对比分析筑坝前后的生态系统结构和功能及其系统特征，探讨筑坝对浮游生物的影响，并应用冗余分析（RDA）分析浮游生物与环境因子的相关性，识别出关键环境因子。结果表明，筑坝对浮游生物有显著影响，具体表现为：（１）浮游生物物种由2007年（筑坝前）的50种增加至2018年（筑坝后）的87种，密度和生物量均增加7.9倍，Shannon-Wiener多样性指数、Pielou均匀度指数均显著增加，但Margalef丰富度指数降低；（２）Ecopath模型结果显示，筑坝后生态系统趋向稳定，其周转率的上升、食物链的转变及混合营养效应的变化是浮游生物变化的重要原因；（３）冗余分析表明，筑坝后总磷（TP）、总氮（TN）、水温（WT）是影响浮游生物群落分布的主要环境因子。     

利用对虾池肥水养殖贝类试验总结

<正> 随着我省对虾养殖业的发展,对虾养殖面积发展到近16万亩。多年来,由于对虾池肥水的利用和处理没有得到应有的重视,大量富营养虾池肥水排入近海海域,使近岸海水富营养化程度日益加重,浮游生物大量繁殖,造成局部赤潮,很大程度上影响了我省近岸海水养殖业的发展。1992年我们承担了江苏省科委下达的“利用对虾池肥水养殖贝类的研究”项目。我们根据贝类的摄食习性,采用虾贝混养、排水河养贝及低洼荒滩围塘蓄水养贝三级贝类过滤法进行了试验研究。所谓三级贝类过滤法:贝类在虾贝混养池中滤掉部分浮游生物(称初级过滤);混养池的肥水排入排水河,在排水河内养殖贝类,贝类进一步滤食掉浮游生物(称二级过滤);排水河的水进入围塘养贝池,围塘里养殖的贝类再进一步滤食掉部分浮游生物(称三级过滤)。通过混养池、排水河、围塘养殖的贝类     

秦山核电温排水对鱼类分布的影响

根据2010年5月(春季)、2010年9月(夏季)和2009年12月(冬季)秦山核电海域渔业资源调查资料以及秦山核电站温排水扩散数学模拟结果,通过秦山核电温排水海域鱼类季节密度的时空分布、优势种、优势种对鱼类总数量的贡献,探讨并分析了秦山核电海域温排水对鱼类分布的影响。结果显示,春季、夏季和冬季的尾数密度分别为5.55×10~3 ind/km~2、22.10×10~3 ind/km~2和10.52×10~3 ind/km~2,重量密度分别为33.80 kg/km~2、59.06 kg/km~2和66.46 kg/km~2。秦山核电海域渔业资源数量季节变化的规律与其他海域相反,冬季最高,春夏季较低,主要与冬季温排水海域具有暖池效应,形成部分鱼类滞留在此越冬有关。温排水平面分布对鱼类分布有重要的影响。主要表现在夏季温排水区域鱼类密度低于其他水域,冬季相反,鱼群滞留在温排水热羽区域,因而显示出温排水海域有较高的鱼群密度。温排水对不同适温习性鱼类影响不同,暖温种能够适应一定的低温,例如,刀鲚(Coilia ectenes)可以在温排水水域越冬,而对高温有耐受性的棘头梅童鱼(Collichthys lucidus)夏季在温排水水域成为优势种。鱼类优势种的适温性决定着鱼群的分布特征,冬季最重要的优势种为刀鲚,在尾数上的贡献率高达45.02,由于该种在温排水的热羽区域分布密集,形成温排水水域鱼群密度大于周边水域的现象。由于温排水改变了渔场环境,导致新的越冬场的形成,有可能形成新的渔汛,引起当地渔场属性的改变。     

阳宗海浮游植物和浮游细菌群落的空间分布特征

浮游植物和浮游细菌在水生态系统的物质循环和能量流动中起重要作用,其分布规律及其驱动机制的识别和比较是评价水生生态系统健康的重要基础。阳宗海2008年经历了大规模的砷污染,且砷浓度目前仍处于超标水平,有必要识别砷污染水体中不同浮游生物群落分布的基本特征及其异同。通过显微镜检和聚合酶链式反应-变性梯度凝胶电泳(PCR-DGGE)方法,探究阳宗海浮游植物和浮游细菌的组成及其空间分布因子。结果表明,蓝藻门在浮游植物中占绝对优势(全湖平均比例为91%),其次是甲藻门、绿藻门、金藻门、硅藻门、隐藻门和裸藻门。对DGGE条带中的DNA片段进行blast比对显示,阳宗海水体中的浮游细菌(异养细菌)主要包含放线菌纲、β-变形菌纲、α-变形菌纲和拟杆菌。PCA分析显示,浮游植物和浮游细菌群落空间分布存在差异,ANOSIM结果表明,南部和中北部的浮游植物群落存在显著差异(P0.05,R=0.48)。多变量统计分析结果显示,空间变量和水温分别单独解释了阳宗海浮游植物群落变化的5.69%和16.51%,砷主要通过与水温和空间距离的相互作用对浮游植物的空间分布产生影响,水环境指标和空间距离与浮游细菌的空间分布没有显著关系(P0.05)。与浮游细菌相比,浮游植物群落相似性存在显著的距离衰减关系(R2=0.61,P0.001),可能与浮游植物扩散能力小于细菌有关。     

秦山核电站温排水附近海域鱼类群落分布空间的差异

根据秦山核电站温排水扩散数学模拟结果以及在秦山核电站附近海域春季(2010年5月)、夏季(2010年9月)和冬季(2009年12月)渔业资源调查资料,通过聚类分析方法对鱼类群落分布进行划分,从不同群落空间分布及种类组成、种类数及多样性的分析等方面,探讨并分析了秦山核电站温排水对附近海域鱼类群落分布的影响。结果显示,春、夏和冬季秦山核电站温排水附近海域均划分为2个群落:温排水影响海域(即群落Ⅰ,以下简称内侧;位于秦山核电站排水口附近,温排水排入水域使水温升高,水温向外侧扩散逐渐降低)和温排水外侧海域(即群落Ⅱ,以下简称外侧)。鱼类群落结构差异表现为春夏季鱼类种类数和多样性指数特征差异一致,外侧高于内侧,数量密度差异较大,夏季和冬季差异明显,呈相异特征。春季鱼类种类数外侧(14种)内侧(6种),尾数和重量多样性指数(Hn′)平均值类似,外侧(2.30和1.93)内侧(1.76和1.56),数量密度差异较大,尾数密度外侧(1.95×103个/km)内侧(0.88×103个/km),而重量密度内侧(6.14 kg/km2)外侧(2.26 kg/km2),主要与春季温排水影响海域鱼类产卵,鱼类在内侧滞留且体质量较大有关;夏季与春季类似,鱼类种类数、尾数和重量多样性指数、尾数和重量密度都是外侧(11种、1.76、1.92、2.57×103个/km和9.06 kg/km2)内侧(9种、1.75、1.65、1.98×103个/km和3.67 kg/km2),主要因为夏季水温较高,温排水进入海域改变内侧鱼类群落特征,表现为内侧低于外侧;而冬季与夏季正相反,各指标都是内侧(15种、1.61、1.86、1.09×103个/km和8.64 kg/km2)外侧(7种、1.24、1.13、0.84×103个/km和4.72 kg/km2),主要与冬季水温较低,温排水影响海域具有暖池效应,形成部分鱼类滞留在此越冬有关。温排水对不同适温性的鱼类影响不同,一些暖温性鱼类能够适应一定的低温,因而在冬季温排水附近海域鱼类暖温种数和种类数(8种和15种)均为三季最高,这与物种在温排水的热羽区域分布密集有关,从而形成温排水附近海域鱼类种类多于其他群落的现象。研究表明,秦山核电站温排水附近海域鱼类群落分布空间差异显著,温排水引起的水温变化是主要原因。     

东海浮游异足类环境适应分析

根据1997~2000年东海23°30′~33°00′N、118°30′~128°00′E海域4个季节海洋调查资料,采用浮游异足类物种丰度和同步的温、盐度数据拟合曲线,构建数学模型,计算物种分布的最适温度和盐度值。同时根据以往对异足类生态特征分析的结论,划分东海浮游异足类各物种的生态类型。结果表明,塔明螺(Atlanta turriculata)和拟翼管螺(Firoloi-da desmaresti)分布在外海,具有高温、高盐的适应特征,是热带大洋种。其他为亚热带外海种,其中玫瑰明螺(Atlantarosea)具广温种特征,明螺(Atlanta peroni)适温偏低,有广盐种的特征,大口明螺(Atlanta lesueuri)分布在盐度较高的水域,扁明螺(Atlanta depressa)具有近海种特征。东海浮游异足类总体上属于典型的暖水性生态类型,温、盐适应范围较窄,对水温和盐度敏感,是较好的指示种。东海浮游异足类主要分布在28°00′~30°00′N,124°00′~126°00′E的海域,绝大多数物种难以逾越冷水水团的阻隔,这是浮游异足类很少在黄渤海出现的主要原因之一。浮游异足类生态类型划分在古气象海洋学、海洋地质、海洋物理和海洋生物学的研究中具有重要的意义。     

Protein and amino acid composition from the mantle of juvenile O ctopus vulgaris exposed to prolonged starvation

Protein and amino acid composition of the mantle of juvenile O ctopus vulgaris (Cuvier, 1797) during fasting for 27 days were determined. Average protein content of octopus mantle was of 711.19 ± 46.80 g kg^?1 DW, and it decreased with increasing fasting days. The non‐essential amino acids content was higher (486.18 ± 11.08 g kg^?1 protein) than essential amino acids (425.82 ± 9.15 g kg^?1 protein) at the start of the experiment (unstarved animals). The results suggest that the amino acid profile of the mantle where the most abundant amino acids are Arg, His, Lys, Gly, Leu and Pro could indicate a prolonged fasting condition (>20 days) or poor nutrition of O . vulgaris. This study supports the idea of using mantle for metabolic needs of starved O . vulgaris suggesting that the degradation pathway of amino acids to pyruvate and tricarboxylic acid cycle intermediates was favoured contrary to the degradation pathway of ketogenic amino acids. Special considerations should be taken concerning Thr, Ile, Ser, Ala, Asx (Asp, Asn), Glx (Glu, Gln) (because of their fast intake) and Lys and His (due to their stable contents) during a prolonged period of fasting.     

美人鱼发光杆菌对凡纳滨对虾非特异性 免疫功能及抗病力的影响

在基础饲料中分别添加0.1%和1%美人鱼发光杆菌灭活菌、0.1%美人鱼发光杆菌活菌配制成3种免疫实验饲料,以基础饲料为空白对照组饲料,每组设3个平行样。对个体质量为(4.83±0.36)g的凡纳滨对虾进行为期20 d的饲养实验,分别在0、5、10、15和20d进行取样,以血清中的酚氧化酶(PO)、酸性磷酸酶(ACP)、碱性磷酸酶(AKP)、超氧化物歧化酶(SOD)和溶菌酶(UL)活性为免疫指标,探讨了美人鱼发光杆菌作为免疫制剂对凡纳滨对虾非特异性免疫效应的影响;在投喂免疫饲料后的第22天,按0.004 2 kg/kg体重的剂量,直接投喂对虾白斑综合征病毒(WSSV)病料,并记录累积死亡率。结果表明,美人鱼发光杆菌免疫实验组对凡纳滨对虾血清中PO、ACP、AKP、UL和SOD活性影响明显高于对照组,并且在饲料中添加美人鱼发光杆菌后,明显提高了对虾抵御WSSV感染的能力。其中0.1%美人鱼发光杆菌活菌实验组的抗病毒感染能力最强,WSSV感染14d内累计死亡率为63.3%±5.8%;而对照组为96.7%±3.3%。研究表明,美人鱼发光杆菌添加在对虾饲料中能提高凡纳滨对虾非特异性免疫水平,增强抵抗疾病的能力,将其作为对虾免疫增强剂具有良好的应用前景。     

Effects of Spirulina platensis as a feed additive on growth and coloration of blue dolphin cichlids (Cyrtocara moorii Boulunger, 1902)

This study was carried out to investigate the effects of replacing fish meal with dietary Spirulina as a feed supplement on the growth performance and coloration of blue dolphin cichlids (Cyrtocara moorii). Five isonitrogenous (47% crude protein) and isocaloric (17.36 kJ/g digestible energy) diets were for formulated to replace FM with 0, 5, 10, 15 and 20% Spirulina (designated as Control, SP5, SP10, SP15 and SP20 respectively) and fed to the fish (initial body weight, 3.15 ± 0.01 g). Fish were randomly distributed into fifteen 120 L aquariums (26.5 ± 1.00°C), 15 fish per aquarium. The diets were tested in triplicate for 12 weeks. Experimental groups were fed twice daily (09:00 and 17:00) by hand to satiation. At the end of the feeding trial, significantly (p < 0.05) higher weight gain (WG), specific growth rate (SGR), protein efficiency ratio (PER) and lower feed conversion ratio (FCR) were observed in fish fed the SP10 diet when compared to the SP20 diet. There was no significant difference in these parameters between the other groups. The skin coloration of blue dolphin cichlid fed a diet containing Spirulina meal was enhanced. The best coloration was observed in the SP15 group. These impressions were objectively validated by chemical determinations of carotenoids extracted from fish skins and passed statistical tests of significance. The study findings show that Spirulina meal does not diminish growth rates except at very high levels.     

Sea bream culture in Egypt; status, constraints and potential

Marine fish farming in Egypt began in 1976 with the culture of gilthead sea bream, (Sparus aurata) as this fish was notably adaptable to brackish and marine pond conditions. Today, marine fish and shrimp farms amount to about 19,000 ha, out of which 42% is already in production while the rest, i.e., 58% is still under construction. In 1997, cultured gilthead sea bream production of 2,250 tons made up 3% of the 75,000 tons total aquaculture catch. In polyculture, usually with the grey mullet and sea bass, gilthead sea bream contributed 440 kg ha^–1 to the total yield of 1,700 kg ha^–1 (26%) over a period of 16 months. For the same period, the yield of monoculture ponds averaged 100 kg ha^–1, while in marine cages, yields ranged from 4–10 kg m³. In 1996–1997, fry of 0.25–1 g and fingerlings 1–10 g with a total of 3 million, were collected from the wild and 1 million fry were produced in the three marine hatcheries out of the four existing ones. The development of sea bream culture in Egypt is now severely inhibited by the shortage of seeds and adequate feeds. Exports of both sea bream and sea bass, during 1994–1996 averaged 1,300 tons per year.     

Dietary thiamin and pyridoxine requirements of fingerling Indian major carp,Cirrhinus mrigala (Hamilton)

Two experiments were conducted to quantify the dietary thiamin (experiment I) and pyridoxine (experiment II) requirements of fingerling Cirrhinus mrigala for 16 weeks. In experiment I, dietary thiamin requirement was determined by feeding seven casein–gelatin‐based diets (400 g kg^?1 CP; 18.69 kJ g^?1 GE) with graded levels of thiamin (0, 0.5, 1, 2, 4, 8 and 16 mg kg^?1 diet) to triplicate groups of fish (6.15 ± 0.37 cm; 1.89 ± 0.12 g). Fish fed diet with 2 mg kg^?1 thiamin had highest specific growth rate (SGR), protein retention (PR), RNA/DNA ratio, haemoglobin (Hb), haematocrit (Hct), RBCs and best feed conversion ratio (FCR). However, highest liver thiamin concentration was recorded in fish fed 4 mg thiamin kg^?1 diet. Broken‐line analysis of SGR, PR and liver thiamin concentrations exhibited the thiamin requirement in the range of 1.79–3.34 mg kg^?1 diet (0.096–0.179 μg thiamin kJ^?1 gross energy). In experiment II, six casein–gelatin‐based diets (400 g kg^?1 CP; 18.69 kJ g^?1 GE) containing graded levels of pyridoxine (0, 2, 4, 6, 8 and 10 mg kg^?1 diet) were fed to triplicate groups of fish (6.35 ± 0.37 cm; 1.97 ± 0.12 g). Fish fed diet containing 6 mg kg^?1 pyridoxine showed best SGR, FCR, PR, RNA/DNA ratio, Hb, Hct and RBCs, whereas maximum liver pyridoxine concentration was recorded in fish fed 8 mg kg^?1 dietary pyridoxine. Broken‐line analysis of SGR, PR and liver pyridoxine concentrations reflected the pyridoxine requirement from 5.63 to 8.61 mg kg^?1 diet. Data generated during this study would be useful in formulating thiamin‐ and pyridoxine‐balanced feeds for the intensive culture of this fish.     

A Minchinia mercenariae‐like parasite infects cockles Cerastoderma edule in Galicia (NW Spain)

The cockle Cerastoderma edule fishery has traditionally been the most important shellfish species in terms of biomass in Galicia (NW Spain). In the course of a survey of the histopathological conditions affecting this species in the Ria of Arousa, a haplosporidan parasite that had not been observed in Galicia was detected in one of the most productive cockle beds of Galicia. Uni‐ and binucleate cells and multinucleate plasmodia were observed in the connective tissue mainly in the digestive area, gills and gonad. The parasite showed low prevalence, and it was not associated with abnormal cockle mortality. Molecular identification showed that this parasite was closely related to the haplosporidan Minchinia mercenariae that had been reported infecting hard clams Mercenaria mercenaria from the Atlantic coast of the United States. The molecular characterization of its SSU rDNA region allowed obtaining a fragment of 1,796 bp showing 98% homology with M. mercenariae parasite. Phylogenetic analysis supported this identification as this parasite was clustered in the same clade as M. mercenariae from the United States and other M. mercenariae‐like sequences from the UK, with bootstrap value of 99%. The occurrence of M. mercenariae‐like parasites infecting molluscs outside the United States is confirmed.     

A novel approach to denitrification processes in a zero-discharge recirculating system for small-scale urban aquaculture

This paper presents an innovative process to solve the nitrate build-up problem in recirculating aquaculture systems (RAS). The novel aspects of the process lie in a denitrification bioreactor system that uses solid cotton wool as the primary carbon source and a unique degassing chamber. In the latter, the water is physically stripped of dissolved gaseous O₂ (by means of a Venturi vacuum tube), and the subsequent denitrification becomes more efficient due to elimination of the problems of oxygen inhibition of denitrification and aerobic consumption of cotton wool. The cotton wool medium also serves as a physical barrier that traps organic particles, which, in turn, act as an additional carbon source for denitrification. Operation in the proposed system gives an extremely low C/N ratio of 0.82 g of cotton wool/g of nitrate N, which contributes to a significant reduction of biofilter volume. The additional advantage of using solid cotton wool as the carbon source is that it does not release organic residuals into the liquid to be recycled. Operation of the system over a long period consistently produced effluents with low nitrate levels (below 10 mg N/l), and there was only a very small need to replace system water. The overall treatment scheme, also incorporating an aerobic nitrification biofilter and a granular filtration device, produced water of excellent quality, i.e., with near-zero levels of nitrite and ammonia, a sufficiently high pH for aquaculture, and low turbidity. The proposed system thus provides a solution for sustainable small-scale, urban aquaculture operation with a very high recovery of water (over 99%) and minimal waste disposal.     

Fertilization by refrigerator stored sperm of the Indian major carp, Labeo calbasu (Hamilton, 1822)

This study reports on the spermatological properties, and on the development of a protocol for refrigerator storage (4°C) of Labeo calbasu (Hamilton, 1822) sperm for artificial breeding. Volume, motility, concentration and pH of the freshly collected sperm were 2.21 ± 0.53 (μL g^?1 of fish weight) (mean ± SD), 95 ± 1 (%), 1.93 ± 0.44 × 10⁹ (cells mL^?1) and 7.56 ± 0.17 respectively. Sperm activation was evaluated at different osmolalities of NaCl solution, and motility ceased completely when osmolality of the extender was ≥287 mOsmol kg^?1. Sperm retained motility for 24, 72 and 108 h, after refrigerator storage when sperm were undiluted, suspended in Alsever's solution and suspended in Alsever's solution containing 5% methanol respectively. Fertilization rate of fresh eggs with sperm stored at 4°C in Alsever's solution and Alsever's solution containing 5% methanol was 77% and 60% with a hatching rate of 60% and 43% respectively. The fertilization and hatching success of the stored sperm suggests potential to use refrigeration for transporting genetic material to hatcheries for artificial breeding of L. calbasu in Bangladesh.     

Effects of metomidate anaesthesia or transfer to pur sea water on plasma parameters in ammonia-exposed Atlantic salmon (Salmo salar L) in sea water

Atlantic salmon (Salmo salar L) postsmolts weighing 150 ± 53 g were exposed to 14–15 mg l^–1 TA-N (total ammonia-N) in sea water in 1 m³ tanks for 24h. Blood samples were then taken A) immediately after the fish were netted from the exposure tanks and stunned by a blow to the head; B) 2–20 min after the fish were transferred to 15 l of an anaesthetic solution of metomidate in ammonia-free sea water; or C) 2–20 min after the fish were transferred to 15 l of ammonia-free sea water. Plasma TA-N level was 18% lower in the anaesthetised fish compared to in the fish sampled directly from the exposure tanks (p 0.05), and accordingly 16% lower in the fish transferred to pure sea water although this difference was not significant (p = 0.07). Plasma glucose level was higher in the fish transferred to pure sea water than in the fish receiving the two other treatments (p 0.05), but plasma urea, osmolality, Na^{+, Cl–, Ca2+ or Mg2+} levels did not vary significantly between the different treatments. Plasma TA-N level increased with time in the fish in the metomidate solution (p 0.02).