云纹石斑鱼(♀)×七带石斑鱼(♂)杂交子一代胚胎发育及仔稚幼鱼形态学观察

以云纹石斑鱼(Epinephelus moara)♀为母本,七带石斑鱼(E.septemfasciatus)♂为父本进行种间远缘杂交,系统观察了杂交子一代胚胎及仔稚幼鱼的生长发育及形态特征。对杂交子一代的胚胎发育按卵裂期、囊胚期、原肠胚期、神经胚期和器官形成期各阶段进行观察,在水温21～22.5℃、盐度29、pH 8～8.1的海水中,整个胚胎发育过程经35 h 20min完成。根据在卵黄囊期、第二背鳍棘和腹鳍棘生长消退过程、鳞片生长、体表色素变化的不同,观察比较了胚后发育的仔鱼期、稚鱼期、幼鱼期形态特征。鱼苗培育至58 d后完成了稚鱼至幼鱼的变态:初孵仔鱼4 d以前为内源性营养(卵黄囊仔鱼);4 d后开口摄食,为外源性营养;(42±2)d基本完成变态进入稚鱼阶段,(58±4)d全身被鳞,进入幼鱼期。同时,用同一母本(云纹石斑鱼)同批卵与同种雄鱼采集的精子授精后获得的受精卵作为对照组,进行孵化和仔稚幼鱼培育,与杂交子一代进行比较,结果发现杂交子一代在仔稚幼鱼阶段生长速度快于云纹石斑鱼,与七带石斑鱼相近。     

云纹石斑鱼(♀)×鞍带石斑鱼(♂)杂交子代胚胎发育及仔稚幼鱼形态观察

对云纹石斑鱼(♀)与鞍带石斑鱼(♂)杂交子代胚胎及仔稚幼鱼的生长发育进行了观察与研究。在水温(22±1)℃、盐度33、p H7.8的海水中,杂交受精卵经过35 h 23min完成整个胚胎发育。胚胎发育可分为卵裂期、囊胚期、原肠期、神经胚期和器官形成期,其中在卵裂期、囊胚期和仔鱼出膜前后,杂交子代胚胎的死亡率较高。杂交石斑鱼的孵化率为91.5%,低于对照组的93.1%;畸形率为10.5%,高于对照组的5.3%。根据杂交子代卵黄囊消失与否、第二背鳍棘和腹鳍棘的生长与收缩、体色和鳞片的出现,可将杂交石斑鱼胎后发育分为:前期仔鱼(0!3日龄)、后期仔鱼(4!27日龄)、稚鱼期(28!45日龄)、幼鱼期(46日龄以后);通过与其亲本早期发育进行比较发现,云纹石斑鱼(♀)与鞍带石斑鱼(♂)杂交子代具有一定的杂交优势。     

[11]斜带石斑鱼亲鱼周年产卵的观察及仔鱼活力判别

对5～7龄斜带石斑鱼(Epinephelus coioides)亲鱼的周年产卵、产卵量、卵质以及初孵仔鱼活力的判别进行了观察研究.亲鱼共231尾,雌、雄、性别不明鱼样的数量比例为88:84:59;养殖于面积为4 000 m2,平均水深为2.0 m的土池中;冬季使用温泉加温管控制水温在18～26℃,夏季通过遮阳网控制水温在26～32℃.结果显示:(1)斜带石斑鱼亲鱼每月均可产卵,在水温25～31℃之间产卵量最多.全年产卵天数共为141 d,总产卵量为184 999.6万粒,平均每尾雌鱼的年产卵量为2 102.3万粒,其中,1月中旬到7月下旬是亲鱼的产卵盛期,共产卵108 d,占全年产卵时间的76.6%;产卵166 133.5万粒,占全年产卵量的89.8%.(2)斜带石斑鱼卵的受精率和孵化率在初夏的产卵盛期可达80%～90%,其他季节一般在30%～60%.(3)测定了15批受精卵所孵化出仔鱼的存活力指数SAI值为3.98～18.30,SAI值与卵的受精率、孵化率呈正相关性;只有SAI值高于6.19的仔鱼才有可能被成功培育成苗.因此,在春夏之交和夏秋之交,水温24～28℃时,选用受精率、孵化率和SAI值较高的受精卵进行人工育苗,获得成功可能性最大.     

云纹石斑鱼(♀)×赤点石斑鱼(♂)杂交子代胚胎发育及生长

通过人工授精技术对云纹石斑鱼(Epinephelus moara,♀)和赤点石斑鱼(E.akaara,♂)进行了杂交实验,并对杂交子代的胚胎发育和生长状况进行了观察。观察结果显示,杂交子代受精卵为圆形、透明、浮性卵,卵径0.858±0.022 mm,有油球一个,居卵中央;在水温26±0.5℃、盐度32、pH 8.2、静水微充气的孵化条件下,胚胎可以正常发育,共经历了受精卵、卵裂、原肠胚、神经胚、器官形成和出膜6个阶段28个时期,历时25h 15 min完成胚胎发育。统计结果显示,杂交石斑鱼的受精率、孵化率和畸形率分别为87.3%、91.6%和9.5%。在仔稚幼鱼生长方面,杂交石斑鱼的生长速度介于云纹石斑鱼和赤点石斑鱼之间,快于云纹石斑鱼而慢于赤点石斑鱼,表现出一定的杂种优势。     

杂交石斑鱼(褐点石斑鱼♀×清水石斑鱼♂)仔、稚鱼的摄食与生长特性

为阐明人工育苗条件下褐点石斑鱼♀×清水石斑鱼♂杂交子代(简称杂交石斑鱼)仔、稚鱼阶段的摄食与生长变化状况,采用随机取样实验生态学方法,在水温27.5～31°C条件下,对人工培育的杂交石斑鱼仔、稚鱼的摄食及生长进行了研究。结果显示,杂交石斑鱼仔、稚鱼具有较强的摄食能力;仔鱼3日龄开口摄食,摄食发生率为40%,之后的仔、稚鱼摄食发生率均为100%。仔、稚鱼摄食量随体质量的增加而逐渐上升,可用二项方程式表达。消化道饱满系数为0.95%～11.26%。仔、稚鱼在1.5 h内可以饱食,仔鱼对轮虫和桡足类的消化时间分别为0.5～1 h和1～2 h,稚鱼对桡足类成体的消化时间为1.5～3.5 h。杂交石斑鱼仔、稚鱼各阶段的日摄食率分别为49.85%(5日龄)、22.55%(10日龄)和15.72%(24日龄),可将其作为杂交石斑鱼仔、稚鱼日投喂量参考依据。杂交石斑鱼仔、稚鱼摄食具有明显的昼夜节律性,白天摄食,夜间不摄食。5日龄和10日龄仔鱼均出现2个摄食高峰,分别为9:00和18:00;24日龄稚鱼仅在中午12:00出现摄食高峰。3～30日龄的仔、稚鱼平均全长日增长率为7.96%,平均体质量日增重率为28.73%。全长、体质量分别与日龄的关系均可用指数方程表达,体质量(y)与全长(x)的回归方程为y=0.037 3x2.537 8,b值接近3,表明杂交石斑鱼仔、稚鱼为等速生长类型。     

饥饿对云纹石斑鱼(Epinephelus moara)卵黄囊期仔鱼摄食和生长的影响

研究了在水温为(23±0.5)℃,盐度为29?30的培育条件下,饥饿胁迫对云纹石斑鱼(Epinephelus moara)仔鱼生长、摄食、存活等一系列的变化。结果显示,2.5日龄体长出现负增长现象,3日龄仔鱼开口摄食,4.5日龄卵黄囊和油球消耗殆尽;仔鱼摄食率随日龄的变化呈先升高后降低,最终为0,最大值出现在卵黄囊和油球消失之后的当天,即5.5日龄仔鱼达到最大初次摄食率,摄食率为66.67%;6日龄仔鱼的初次摄食率为最大初次摄食率的1/2,仔鱼达到不可逆点,其混合营养的时间为2?3 d,即仔鱼初次摄食率发生到达不可逆点的时间为2.5 d;云纹石斑鱼仔鱼孵化出膜后的3?6 d为其摄食的重要时期。     

饥饿对云纹石斑鱼(Epinephelus moara)卵黄囊期仔鱼摄食和生长的影响

研究了在水温为(23±0.5)℃,盐度为29-30的培育条件下,饥饿胁迫对云纹石斑鱼(Epinephelus moara)仔鱼生长、摄食、存活等一系列的变化。结果显示,2.5日龄体长出现负增长现象,3日龄仔鱼开口摄食,4.5日龄卵黄囊和油球消耗殆尽;仔鱼摄食率随日龄的变化呈先升高后降低,最终为0,最大值出现在卵黄囊和油球消失之后的当天,即5.5日龄仔鱼达到最大初次摄食率,摄食率为66.67%;6日龄仔鱼的初次摄食率为最大初次摄食率的1/2,仔鱼达到不可逆点,其混合营养的时间为2-3 d,即仔鱼初次摄食率发生到达不可逆点的时间为2.5 d;云纹石斑鱼仔鱼孵化出膜后的3-6 d为其摄食的重要时期。     

鞍带石斑鱼(♀)×云纹石斑鱼(♂)杂交后代早期发育及正反交后代生长特性

以鞍带石斑鱼为母本,云纹石斑鱼为父本,采用人工授精技术进行了种间反交实验,并对反交子代的胚胎发育和仔稚幼鱼的生长情况进行了观察,进而与亲本及正交F1云龙石斑鱼(♀)×鞍带石斑鱼(♂)的表型性状进行对比分析。结果显示,反交子代受精卵为圆形、透明、浮性卵,卵径为(0.787±0.013) mm,有1个油球,居卵中央,在水温为24°C、盐度30、pH为7.8的孵化条件下,胚胎可以正常发育,经历受精卵、卵裂、囊胚、原肠胚、器官形成和出膜6个阶段25个时期完成胚胎发育,初孵仔鱼全长为(1.595±0.015)mm,说明反交的可行性。孵化后3 d,卵黄囊消失,由前期仔鱼发育为后期仔鱼,全长(2.530±0.023) mm。孵化后52 d进入稚鱼期,全长(17.500±1.915) mm,第二背鳍棘长(5.795±0.049) mm,第一腹鳍棘长(2.992±0.911) mm;58 d稚鱼背鳍棘收缩至最小值(4.460±0.600) mm时,鳞片和体色开始出现。孵化后67 d进入幼鱼期,全长(34.500±1.291)mm,第二背鳍棘和第一腹鳍棘完全退化,体型与成鱼相似,全身覆盖鳞片,反交F_1体色不一致,具4种表现型。生长对比结果显示,正反交F_1的发育速率均介于亲本之间,均快于云纹石斑鱼,慢于鞍带石斑鱼,反交F_1生长速率慢于正交F_1。研究结果为石斑鱼杂交优势性状形成及遗传解析提供了一定数据基础。     

乌苏里江唇(鱼骨)的全人工繁育

从乌苏里江捕获野生唇(鱼骨)(Hemibarbus labo)亲鱼150余尾,经人工繁殖获得鱼苗,饲养于池塘中,研究其在人工养殖条件下的生长、繁殖和性腺发育等生物学特性.结果表明,野生亲鱼及其F1在池塘中饲养下,性腺可自然发育至成熟,繁殖季节(5-6月)雌、雄亲鱼会出现明显的副性征,注射催产激素HCG、LRH-A2和DOM的混合制剂,可促使成熟的雌性亲鱼产卵,水温22～26℃时,药物的效应时间在17～22 h,人工繁殖的催产率、受精率、孵化率和畸形率分别为87.55%、68.95%、92.5%和5.75%.唇(鱼骨)的卵为圆形、灰白色或淡绿色,遇水后产生较强的黏性,吸水膨胀卵径为(2.32±0.12)mm(n=50),体质量400～900 g的雌性亲鱼绝对怀卵量为(3.19±0.85)×104粒(n=15).水温22～24℃时,从卵授精到仔鱼孵出需要积温69.43℃·d,到仔鱼平游摄食需要积温139.25℃·d,刚出膜的仔鱼全长(6.1±0.3)mm,平游时全长达到(8.9±0.4)mm.在哈尔滨地区人工池塘养殖唇(鱼骨),1+龄鱼体质量为(17.20±2.46)g,2+龄鱼为(89.84±9.30)g,3+龄鱼为(234.94±25.94)g,4+龄鱼为(371.57±64.65)g;雄性3+、雌性4+有部分个体性腺成熟,5+龄时多数个体可发育至性成熟.唇(鱼骨)的全人工繁育成功,可初步解决苗种来源和池塘养殖问题,并为野生资源的增殖和人工规模化养殖奠定基础.     

伊犁裂腹鱼胚胎及早期仔鱼发育的观察

2010年5月通过人工催产,人工授精方法获得伊犁裂腹鱼(Schizothorax pseudaksaiensis Herzenstein)受精卵,在人工培育的条件下对其胚胎和仔鱼发育进行观察.结果显示:伊犁裂腹鱼成熟卵为淡黄色,卵径为1.70～1.80 mm.受精40 min后,受精卵卵周隙接近最大化,此时卵径为2.9...     

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.     

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.     

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.     

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).