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。

     

鲢小清蛋白的cDNA克隆及在大肠杆菌中的原核表达

以鲢(Hypophthalmichthys molitrix)肌肉cDNA为模板, 利用小清蛋白特异性引物进行PCR扩增, 克隆得到β小清蛋白两种不同亚型, 即Ⅰ型、Ⅱ型编码区基因。将目的基因片段连接到pET28a (+)表达载体, 并在大肠杆菌[E.coli BL21 (DE3)]中诱导表达。结果表明, 经诱导的小清蛋白重组质粒菌株有特异的蛋白表达。SDS-PAGE分析显示, 目的蛋白的分子量约为13 kD, 与预期大小一致。菌体超声破碎后发现2种亚型的小清蛋白均为可溶表达。利用Ni²⁺亲和层析柱对重组蛋白进行纯化, 得到高纯度的重组小清蛋白PVⅠ和PVⅡ。经Western Blot 鉴定, 重组小清蛋白PVⅠ和PVⅡ均能与抗鲢小清蛋白单克隆抗体反应。本研究为进一步分析小清蛋白的结构与致敏性的关系提供了重要的基础。

     

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。

     

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。

     

人工纳米材料对水生生物毒性的研究进展

近年来纳米技术发展迅速, 人工纳米材料(MNMs)在生物医学、航空航天和建筑等领域中广泛应用。然而, 随着大量MNMs不断进入水环境, 人工纳米粒子对水生生物的毒性效应已引起人们的关注。通过调研人工纳米粒子对水生生物毒性的最新研究成果, 重点对人工纳米粒子在5个方面对水生生物的毒性效应进行综述: 1) 对水生生物个体生长的毒性效应; 2) 对肝组织、鳃组织和脑组织等在组织细胞水平的毒性效应; 3) 在分子和基因水平上对DNA结构、mRNA和相关蛋白质表达的影响; 4) 对水生生物的生殖毒性效应和机制; 5) 对其他生理作用如光合作用和呼吸作用的毒性影响。同时还分析了MNMs对食物链的影响, 进一步对MNMs在水体环境中的毒理学发展方向进行了展望, 以期为中国学者在相关领域的研究工作提供参考与借鉴。

     

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。

     

大眼鳜与翘嘴鳜正反交及其正交子代自交的胚胎发育观察

对大眼鳜(Siniperca kneri)(♀)×翘嘴鳜(Siniperca chuatsi)(♂)正交F1(DQ)、翘嘴鳜(♀)×大眼鳜(♂)反交F1(QD)、大眼鳜(♀)×翘嘴鳜(♂)正交F1的自交F2(F2)的胚胎发育进行观察, 详细记录了受精卵、分裂期、囊胚期、原肠胚期、胚体形成期、破膜期6个胚胎发育时期的卵径、孵化破膜时间、初孵仔鱼大小以及胚胎发育特征。大眼鳜受精卵卵径为(1.231±0.057) mm, 翘嘴鳜卵径为(1.197±0.052) mm, 显著大于正交F1雌鱼的卵径(1.723±0.0519) mm(P<0.05)。DQ受精卵在水温25.5~27.7℃经过37 h孵化破膜, QD受精卵在水温27.5~28.7℃经过30 h孵化破膜, F2受精卵在21.6~24.1℃经过40 h 57 min孵化破膜。DQ、QD、F2初孵仔鱼大小分别为(4.1±0.4) mm、(4.0±0.2) mm、(3.5±0.2) mm。鳜属鱼类中翘嘴鳜与大眼鳜胚胎发育各时期特征基本一致, 3种杂交鳜胚胎发育特征与其父母本也基本一致。经过比较发现, 其色素的形成与运动有鳜属的特异性: 在胚孔封闭后, 黑色素开始形成并逐渐扩散覆盖整个卵黄囊, 中期黑色素呈现星芒状, 并在油球处有集中现象, 后期色素则逐渐出现在眼和头部。水温21.6~28.7℃时3种杂交鳜的胚胎发育时间都偏向与翘嘴鳜的胚胎发育时间一致, 在水温23~26.5℃时DQ、F2与大眼鳜的胚胎发育时间有较大差别。

     

不同技术处理的钝齿短浆蟹淋巴液中和麻痹性贝毒毒性的效果

钝齿短浆蟹(Thalamita crenata)淋巴液可以中和麻痹性贝毒(PSP)的毒性, 这个信息为PSP的降毒研究提供重要依据, 但是淋巴液处理方法是否对其毒性中和效果有影响尚不清楚。本研究采用小鼠腹腔注射法, 以淋巴液的PSP毒性中和效果为指标, 探讨抗凝剂、提取方法和冻存条件等淋巴液处理方法对其PSP毒性中和效果的影响, 为蟹淋巴液的制备提供科学依据。分析结果显示, 不同抗凝剂对淋巴液的PSP毒性中和效果有不同程度的影响, 其中EDTA抗凝剂对淋巴液的PSP毒性中和效果最好, 相对于对照组(小鼠致死时间在5 min左右), PSP-EDTA-淋巴液组的小鼠均存活。低浓度EDTA (5 mmol/L)即可起到抗凝作用并保持淋巴液较好的PSP毒性中和效果, EDTA浓度过高反而对PSP毒性中和效果产生抑制作用。在低浓度EDTA条件下, 针头抽取淋巴液的PSP毒性中和效果明显优于组织破碎法。EDTA浓度为5 mmol/L时, 在针头抽取淋巴液组中, 67%的小鼠致死时间超过30 min。相比之下, 组织破碎提取的淋巴液组的小鼠致死时间均分布在8.1~24 min。另外, 蔗糖对淋巴液的冻存起到较好的抗冷冻保护作用。以上结果表明淋巴液处理方法对其麻痹性贝毒毒性中和效果有较大影响。

     

太平洋牡蛎不同组织DNA甲基化的F-MSAP分析

采用荧光标记的甲基化敏感性扩增多态性(F-MSAP)技术对太平洋牡蛎(Crassostrea gigas)的6个组织进行全基因组CCGG位点甲基化水平的检测。结果表明: 鳃、闭壳肌、外套膜、唇瓣、性腺、消化盲囊6个组织的甲基化水平分别为: 31.77%、36.41%、32.00%、36.47%、32.77%和37.92%。甲基化模式分为全甲基化和半甲基化, 在太平洋牡蛎中, 全甲基化模式与总体甲基化水平一致, 消化盲囊、唇瓣、闭壳肌组织的甲基化水平较高, 而鳃、外套膜、性腺组织的甲基化程度较低; 半甲基化位点显著少于全甲基化位点, 并且不同组织间的半甲基化位点不存在显著性差异, 而从全甲基化位点及总甲基化水平分析, 不同组织之间甲基化水平差异显著。太平洋牡蛎中存在组织特异性甲基化片段和非组织特异性甲基化片段, 但却只在一个或部分个体中出现, 没有发现在所有研究个体中都存在的甲基化差异片段, 这可能与牡蛎较高的杂合度相关。对实验样品进行的荧光标记的扩增片段长度多态性(F-AFLP)分析发现, 样品间的确存在较大的遗传差异, 基于以上结果可以推测基因组甲基化水平可能与个体遗传背景相关联。

     

牙鲆连续三代抗鳗弧菌病家系的筛选与分析

为了培育牙鲆(Paralichthys olivaceus)抗鳗弧菌(Vibrio anguillarum)病的品系或品种, 2009和2012年利用中国牙鲆抗病群体、从日本和韩国引进的牙鲆群体以及2007年和2009年从大量牙鲆家系中选留的优良家系为亲本, 通过巢式杂交、三元杂交及雌核发育等方法, 分别于2009年和2012年建成牙鲆家系43个和65个, 选取2009年的33个家系和2012年的43个家系进行鳗弧菌感染实验, 共筛选出13个抗病家系, 其中3个家系的存活率极显著高于对照组(P<0.01), 另外10个家系的存活率显著高于对照组(P<0.05), 这13个家系包含F3家系、雌核发育一代和二代家系各1个, F2家系3个, 在以上6个家系中,除了1个F2家系, 其他家系的亲本均来自于抗病家系且鳗弧菌感染存活率的变异系数都低于10%。对连续三代抗病家系进行分析, 发现在上述13个抗病家系和2007年筛选出的3个抗病家系共16个抗病家系中有13个家系来自于中国牙鲆抗病群体相关, 结果表明, 部分F1、F2、F3和雌核发育家系较好地遗传了其亲本的抗病性能, 抗病性能稳定, 为培育抗鳗弧菌病的牙鲆品系或品种奠定了基础。

     

芳香化酶抑制剂对暗纹东方鲀CYP19A、DMRT1基因表达及性腺分化的影响

采用组织学和分子生物学方法,研究了投喂芳香化酶抑制剂来曲唑(LE)后暗纹东方鲀(Takifugu obscures)初孵仔鱼CYP19A、DMRT1基因表达以及性腺的组织学变化,以期进一步了解P450芳香化酶(P450arom)在鱼类早期性别分化过程中的作用。RT-PCR结果显示,对照组样品CYP19A和DMRT1表达显示性二态,雌性表达CYP19A基因,雄性表达DMRT1基因。LE处理组在性别分化期间,雄性样品单一表达DMRT1,雌性样品则同时表达CYP19A和DMRT1。qRT-PCR结果显示:LE处理组雌性仔鱼CYP19A基因表达被显著抑;虽然在仔鱼出膜后22d(dph)的表达水平高于9 dph,但仅为同日对照组的2.11%。LE处理组雌性样品22 dph时DMRT1基因表达量上调,至150 dph时达对照组雄性水平。55 dph的性腺组织学结果表明,LE处理可导致暗纹东方鲀稚鱼原始卵巢退化,并向功能性精巢发育。150 dph的LE处理组性腺均为精巢,并与对照组精巢发育同步。结论认为,暗纹东方鲀性腺分化期间P450arom是卵巢形成和维持发育所必须的,抑制P450arom活性可导致雌性暗纹东方鲀发生雄性化逆转。     

Studies on feminization,sex determination,and differentiation of the Southern catfish, <Emphasis Type="Italic">Silurus meridionalis</Emphasis>—a review

The sex ratio of the feral Southern catfish was reported to be about 1:1, while the fish obtained by artificial fertilization were always female. Hence, we examined the possible influence of the micro-environment during artificial insemination (pH of the ovarian fluid and concentration of the semen) and early development (feed, hatching temperature, and water) on the sex ratio of Southern catfish fry. In order to examine the possibility of the occurrence of gynogenesis during artificial propagation, cytological observations on the insemination processes and the artificial induction of gynogenesis were also performed. However, no male fish were obtained even in these experiments, excluding the possibilities of these micro-environmental changes on catfish sex ratio and the occurrence of gynogenesis during artificial propagation. Female-to-male sex reversal was achieved by treatment with fadrozole (an aromatase inhibitor) and tamoxifen (an estrogen receptor antagonist). Histological analyses on the gonadal development of both female and induced male fish were subsequently performed. Moreover, several genes involved in sex differentiation, such as dmrt1, foxl2, and cyp19, and three subunits of gonadotropin (gth), i.e., gthα, lhβ, and fshβ, were isolated. Their expression patterns were studied under normal gonadal development and sex reversal conditions. The results revealed that dmrt1, foxl2, and cyp19a were closely related to catfish sex differentiation, and the gth subunits were possibly related to ovarian differentiation and oocyte development. Taken together, we hypothesized that estrogen was highly responsible for the ovarian differentiation and feminization of catfish fry under artificial propagation, although the mechanism involved remains elusive.     

Effects of a nonsteroidal aromatase inhibitor on gonadal differentiation of bluegill sunfish Lepomis macrochirus

In the present study, the efficacy of Letrozole, a potent nonsteroidal aromatase inhibitor (AI), on gonadal sex differentiation and sex reversal was examined in bluegill sunfish (Lepomis macrochirus). In Experiment 1, using AI diet treatments (50, 150, 250 and 500 mg kg⁻¹) from 30 to 90 days posthatch (dph), AI interrupted ovarian cavity formation at a dose of 500 mg kg¹ diet and one intersex fish was identified in this group. The proportions of males in all the treated groups were significantly higher than those in the control group. In Experiment 2, using AI immersion treatments (250, 500 and 1000 μg L⁻¹) during 30–50 dph, the treated groups of 500 and 1000 μg L⁻¹ produced significantly more males than the control and 250 μg L⁻¹ groups. Histological examination revealed no differences in ovary or testis tissue between control and AI‐treated fish. There were no significant differences detected in body weight and length among the AI treated and control groups (P>0.05) for both experiments. The results from these two experiments suggest that inhibition of aromatase activity by AI could influence sex differentiation in bluegill sunfish.     

Gonadal morphogenesis and sex differentiation in cultured chub mackerel,Scomber japonicus

The timing of primordial germ‐cell (PGC) migration with regard to the gonadal anlagen, gonad formation and sex differentiation was examined histologically in the chub mackerel (Scomber japonicus) at 5–190 days post hatching (dph). At 5 dph, PGCs appeared on the peritoneal epithelium surface or in the mesentery, on the dorsal side of the abdominal cavity. By 10 dph, stromal cells around the PGCs proliferated. The gonadal primordium was formed by 15 dph. The gonadosomatic index was 0.01% at 30 dph and increased thereafter (0.32% in females and 0.04% in males at 160 dph). Ovarian differentiation occurred at 30–40 dph, indicated by ovarian cavity formation (elongation and fusion of the upper and lower ovarian edges). Meiosis was subsequently initiated. A few meiotic oocytes surrounded the cavity at 50 dph; most were in the perinucleolus stage at 60 dph and attained a diameter of 60–70 μm at 190 dph. Testicular differentiation occurred at 30 dph, indicated by the formation of the sperm duct primordium. Spermatogonia gradually proliferated, developing into spermatocytes at the chromatin–nucleolus stage (after 90 dph) and subsequently into spermatids and spermatozoa (160 dph). These data could aid the development of seeding and cell‐engineering technologies for scombrid fish.     

Evaluation of a 40 day Assay for Testing Endocrine Disrupters: Effects of an Anti-Estrogen and an Aromatase Inhibitor on Sex Ratio and Vitellogenin Concentrations in Juvenile Zebrafish (Danio rerio)

In the present study, the effects of the anti-estrogen ZM 189,156 and the aromatase inhibitor fadrozole were evaluated in a 40-day juvenile assay developed for screening of endocrine disrupting chemicals. Juvenile zebrafish were exposed from 20 to 60 days post hatch (dph) to ZM 189, 154 (100 μg l⁻¹ and 200 μg l⁻¹) and fadrozole (10, 32, and 100 μg l⁻¹). VTG concentrations were measured at 38 dph by the use of a direct non-competitive sandwich ELISA and sex ratios were determined at 60 dph by histological examination of the gonads. A small but significant increase in VTG concentrations was observed in fish exposed to ZM 189, 156 (100 and 200 μg l⁻¹) and fadrozole (10 and 100 μg l⁻¹) compared to control groups. In fish exposed to ZM 189, 156 and fadrozole, the percentage of females declined and the number of undifferentiated fish increased. These findings show that exposure of juvenile zebrafish to an aromatase inhibitor or an anti-estrogen during early development inhibits differentiation and development of female gonads. The data presented, furthermore, show that the 40-day juvenile assay may be suitable for screening endocrine disrupting chemicals acting as anti-estrogens and aromatase inhibitors.     

暗纹东方鲀芳香化酶基因的结构及表达分析

性腺型芳香化酶基因是一种调节雌雄激素平衡的基因。为初步探究暗纹东方鲀性腺型芳香化酶基因在性腺发育和性别分化过程中的作用,通过RACE及荧光定量PCR技术,成功克隆出暗纹东方鲀性腺型芳香化酶基因的cDNA全长序列,共1786 bp,编码514个氨基酸,与红鳍东方鲀及星点东方鲀同源性最高。氨基酸序列分析显示,该基因编码的蛋白是一种稳定的亲水性蛋白,但不存在信号肽序列;性腺型芳香化酶含有38个磷酸化位点、4个N-糖基化位点、2个跨膜保守结构域;其氨基酸序列在哺乳动物和鱼类中均十分保守,且含有跨膜区、Ⅰ-螺旋区、Ozol′s肽区、芳香化酶特异性保守区和亚铁血红素结合区等功能保守区。表达分析显示,暗纹东方鲀性腺型芳香化酶基因主要在肌肉和卵巢中表达,其次在其他组织中也有少量表达,而且在幼鱼不同发育期卵巢中的表达量呈现出逐渐升高再降低的表达趋势,在精巢中则基本不表达。研究结果表明,性腺型芳香化酶基因很可能参与了暗纹东方鲀雌鱼性腺分化后卵巢的发育、雌性特征的维持和其他组织的发育等过程。     

Increase in estrogen signaling in the early brain of orange-spotted grouper Epinephelus coioides: a mini-review

Despite neurosteroidogenic enzymes are playing important roles in the regulation of brain development and function, the potential link between brain and gonad by the action of steroid hormones during gonadal sex differentiation is still not clear in teleosts. In this mini-review, we summarized our understanding on the early brain development related to the synthesis of neurosteroids and receptor signaling during gonadal sex differentiation in protogynous orange-spotted grouper, Epinephelus coioides (functional females for the first 6 years of life and start to sex change around the age of 7 years) and protandrous black porgy (functional males for the first 2 years of life but begin to change sex during the third year). We found a similar profile in the increased expression of brain aromatase gene (aromatatse B or cyp19a1b), aromatase activity, estradiol (E₂), and estrogen signaling in the brain of both grouper and black porgy fish during gonadal sex differentiation. In contrast to mammals, teleost fish Cyp19a1b expressed in a unique cell type, a radial glial cell, which is acted as progenitors in the brain of developing and adult fish. In agreement with these pioneer studies, we demonstrated that the grouper cyp19a1b/Cyp19a1b was expressed in radial glial cells. Further, in vivo data in the grouper brain showed that exogenous E₂ upregulated Cyp19a1b immunoreactivity (ir) in radial glial cells. These data suggest the possible roles of Cyp19a1b and E₂ in early brain development which is presumably related to gonadal sex differentiation.     

Effects of Natural EstradioI-17β and Synthetic 17α- Ethynylestradiol on Direct Feminization of European Sea Bass Dicentrarchus labrax

To produce a monosex female population of European sea bass Dicentrarchus labrax, fry were fed dry diets containing dosages of 12.5, 25, and 50 mg/kg food of either the natural estrogen estradiol-170β(E₂) or the synthetic estrogen 17α-ethynylestradiol (EE₂) for 60 d starting at 88 d post-hatch (dph). A complete feminization (100%) was achieved in all E₂-treated groups at the age of 11 mo (330 dph). All affected fish had ovaries similar in size and histological structure to those of control females. In the E₂-treated groups, feminized fish were heavier and longer than untreated controls (males and females combined). In control groups females exhibited significantly higher body weight and total length than males. Untreated females from control groups and females from the group treated with E₂ at 12.5 mg/kg food had similar body weight, suggesting that in sea bass growth is related to phenotypic sex. In the Entreated groups, survival rates were similar to those of the control fish. A relatively high percentage of females was obtained in the EE₂-treated groups (from 38.6 to 96.5%). However, the gonadal development in these fish was significantly suppressed and a dose-dependent reduction of gonadal sizes was evident. Treatments with the EE₂ (12-5, 25, and 50 mg/kg food) resulted in many fish having abnormal (2.9-5.4-39.8%, respectively) and sterile (0.6-6.0-21.6%, respectively) gonads. Effects also included significantly lower weight and shorter length when compared with controls. Furthermore, fish fed with EE₂ at the dosage of 50 mg/kg food had high mortality rate. A simple protocol was developed for the complete feminization in sea bass in which the fry (80-100 dph) were fed to satiation two times daily with a diet containing 12.5 me of E₂/ks food for a period of 60 d.