基于叶绿素a时空分布的胶州湾菲律宾蛤仔养殖容量评估

2017年7月~2019年4月期间，本研究采用大面观测、现场模拟实验与生长情况跟踪相结合的手段，基于Dame指标和Herman模型估算了胶州湾菲律宾蛤仔(Ruditapes philippinarum)的养殖容量。结果显示，调查期间，胶州湾水体的叶绿素a浓度为2.09~4.28 mg/m3，均值为3.07 mg/m3；不同规格(壳长2.29~3.59 cm)的菲律宾蛤仔单位个体的平均滤水率为0.45 L/(h?ind.)，单位重量菲律宾蛤仔的平均滤水率为2.52 L/(g?h)；菲律宾蛤仔1龄、2龄和3龄的平均干重分别为0.18、0.30和0.42 g；胶州湾的水团停留时间为52 d，初级生产时间为1.58 d，贝类滤水时间为2.09 d；1龄、2龄和3龄蛤仔的养殖容量分别为637、378和272 ind./m2。目前，菲律宾蛤仔养殖量已超过养殖容量，建议若以2龄蛤为采捕对象，适宜的播苗密度为582 ind./m2；若以3龄蛤为采捕对象，适宜的播苗密度为789 ind./m2。本研究结果可为保障胶州湾菲律宾蛤仔养殖产业的绿色高质量发展提供理论依据和数据支撑。     

基于生态模型估算胶州湾菲律宾蛤仔养殖容量

贝类的养殖容量是养殖功能海域的生态系统所能容纳的最大养殖个体数量。本文由实测资料建立了胶州湾生态模型,计算了浮游植物生物量,进而依据饵料收支平衡关系,估算了胶州湾菲律宾蛤仔的养殖容量,研究结果表明,各养殖区不同规格蛤仔的养殖容量在1月或3月份最大,9月份最小;胶州湾5个养殖区内,2~2.6cm、2.6~3.3cm和3.3~4cm 3种壳长规格菲律宾蛤仔的平均养殖容量分别为603枚/m2、441枚/m2和362枚/m2,胶州湾菲律宾蛤仔的播放密度已经饱和;为了保持最大产量、提高养殖品质的同时并将苗种成本降至最低,可适当降低播放密度;建议红岛东、红岛南、红岛西、胶州、黄岛等5个养殖区菲律宾蛤仔的放养密度分别为718枚/m2、693枚/m2、557枚/m2、805枚/m2和654枚/m2,胶州湾平均放养密度为690枚/m2。     

胶州湾菲律宾蛤仔生态容量评估及其碳汇功能

胶州湾是我国重要的菲律宾蛤仔(Ruditapes philippinarum)养殖基地,为探究湾内菲律宾蛤仔的生态容量及其碳汇功能,本研究采用Ecopath模型法评估了胶州湾菲律宾蛤仔的生态容量,并利用Ecosim模块动态分析了菲律宾蛤仔生物量扩大对胶州湾生态系统结构与功能特征的潜在影响,同时估算了胶州湾菲律宾蛤仔个体及种群水平的碳收支情况。结果显示,胶州湾菲律宾蛤仔的生态容量为239.9 t/km2,虽然整体水平尚未达到生态容量,但局部养殖区域已远超出了菲律宾蛤仔的生态容量;当胶州湾菲律宾蛤仔生物量从当前增加至生态容量时,生态系统总流量、容量、优势度和循环指数分别提高了16.0%、3.9%、47.1%和103.0%,而熵值降低了10.4%,表明此时生态系统具有更高的成熟度与稳定性,但菲律宾蛤仔生物量扩大至生态容量10倍时会对生态系统产生不利影响甚至崩溃;菲律宾蛤仔个体在1个养殖周期内约摄取3 310.1 mg C,其中约46.2%的碳沉降至海底,约13.2%的碳通过收获移出,如按菲律宾蛤仔生物量达到生态容量时计算,胶州湾每年将有1.5万t碳以生物沉积形式沉降至海底,有0.6万t碳以收获形式移出。研究结果为指导菲律宾蛤仔增养殖产业的健康可持续发展、阐明菲律宾蛤仔的碳汇功能提供了理论依据与数据支撑     

乳山湾滩涂贝类养殖容量的估算

通过计算单位面积的浮游植物和底栖微藻生产的有机碳供应量、单位面积浮游动物和其它底栖生物的生物量及其对有机碳的需求量,首次对乳山湾滩涂贝类(以菲律宾蛤仔为代表,后文简称蛤仔)在不同养殖季节的养殖容量进行了估算。结果显示,不同体长范围内的蛤仔养殖容量均表现为10月份最大,6月份次之,8月份最小。壳长在1.5~2.5 cm范围内的蛤仔的平均养殖容量为2 692 ind.m-2,目前乳山湾蛤仔实际养殖密度为1 080 ind.m-2,该体长范围内的蛤仔养殖密度尚有较大发展余地;壳长在2.5~3.5 cm范围内的蛤仔的平均养殖容量为1157 ind.m-2,该体长范围内的蛤仔养殖密度基本接近其实际养殖密度;壳长大于3.5 cm的蛤仔平均养殖容量为697 ind.m-2,该体长范围内的蛤仔养殖密度已超过其最佳养殖密度。     

鸭绿江口浅海海域菲律宾蛤仔养殖容量估算

通过对鸭绿江口海域初级生产力生产量,浮游植物、浮游动物和底栖生物的丰度和生物量的调查,根据PARSONS-TAKAHASHⅡ营养动态模型Q=(BEn)×k,对鸭绿江口浅海菲律宾蛤仔养殖容量进行了估算.研究结果表明,不同季节壳长1.5、2.0、2.5cm的菲律宾蛤仔年养殖容量分别为189 356.60、221 970.71、249 717.05t,养殖容量春季最大,秋季次之,夏季最小.春季单位面积可放养菲律宾蛤仔:滩涂养殖平均为1.48 kg/m2,深水养殖为1.17 kg/m2;夏季单位面积可放养的菲律宾蛤仔:滩涂养殖平均为0.17 kg/m2,深水养殖为0.32 kg/m2.该区域菲律宾蛤仔实际养殖密度已经大大超过其单位面积最佳放养容量,这也是导致该区域菲律宾蛤仔疾病频发和死亡率高的主要原因.     

胶州湾底栖生态系统健康评价——基于大型底栖动物生态学特征

根据2017年7月山东省胶州湾海域的大型底栖动物调查数据，应用聚类分析、生物多样性和Multivariate-AZTI’s Marine Biotic Index (M-AMBI)等方法分析了大型底栖动物的生态学特征，评估了胶州湾底栖生态系统的健康状况。结果显示，调查海域共采集到大型底栖动物64种，其中，多毛类25种，甲壳动物23种，软体动物9种，棘皮动物和其他类群共7种。该海域大型底栖动物生物量和丰度的平均值分别为70.0 g/m2和132 ind./m2，菲律宾蛤仔(Ruditapes philippinarum)、寡鳃齿吻沙蚕(Nephthys oligobranchia)和纽虫(Nemertinea)是优势种。物种多样性指数( )为0.69~3.77，平均值为2.35，丰富度指数(d)为0.67~3.12，平均值为1.56，Pielou均匀度指数(J)为0.25~1.00，平均值为0.81。多样性AMBI指数(M-AMBI)为0.26~0.60，平均值为0.44。根据CLUSTER分析结果，在15%相似水平上可将研究站位划分为3个群落，菲律宾蛤仔养殖密度较大的站位群落结构较为相似，被划分在同一个群落中，聚类结果与菲律宾蛤仔养殖密切相关。大型底栖动物群落的多样性指数和M-AMBI指数分析显示，胶州湾海域底栖生态系统受到中等程度的干扰。     

胶州湾菲律宾蛤仔个体生长模型的构建与验证

为更好地掌握胶州湾菲律宾蛤仔(Ruditapes philippinarum)的动态生长情况，本研究基于动态能量收支(Dynamic energy budget, DEB)理论，利用python软件构建了菲律宾蛤仔的个体生长模型，以2018年4月24日~2019年1月9日观测的胶州湾海域叶绿素a和水温为强制函数，通过现场实验和已有文献报道获取模型参数，模拟了菲律宾蛤仔软体组织质量和壳长的生长情况，并根据胶州湾海域菲律宾蛤仔生长的实测数据对模型进行了验证。结果表明，构建的个体生长模型能够很好地模拟胶州湾海域菲律宾蛤仔软体组织干重和壳长的生长，软体组织干重和壳长的模拟值与实测值呈显著线性相关关系(P<0.01)，R2分别为0.9374和0.9168。敏感度指数最高的是阿伦纽斯温度TA和参考温度T1，如果TA和T1分别改变10%，菲律宾蛤仔软体组织干重增加高达8.86%。研究结果为后续开展基于生态系统动力学模型的养殖容量动态评估提供了基础模块和数据支撑。     

福建诏安湾贝类养殖容量的研究

通过现场对诏安湾叶绿素a含量、初级生产力、生态效率、浮游植物有机碳含量、养殖贝类有机碳含量及其含壳重与鲜组织重比值、养殖贝类和野生滤食性动物滤水率、潮间带和潮下带及吊养区附着滤食性动物现存量等的调查获得模型参数,应用营养动态模型、沿岸能流模型估算贝类生态容量,进而扣除野生滤食性动物现存量形成贝类的养殖容量,同时采用贝类能量收支模型估算贝类养殖容量。3种模式估算的贝类养殖容量分别为58469t,288260×104ind;60275t,297167×104ind;61532t,30336×104ind;平均60092t,296263×104ind。并且采用统计分析法估算贝类及其各品种的适养面积。贝类适养总面积为2755hm2,其中缢蛏25hm2,牡蛎1560hm2,翡翠贻贝215hm2,菲律宾蛤仔120hm2,泥蚶30hm2,凸壳肌蛤95hm2,波纹巴非蛤710hm2。     

桑沟湾楮岛大叶藻床区域菲律宾蛤仔的生态贡献

桑沟湾楮岛大叶藻(Zostera marina L.)床周边存在大量的底栖菲律宾蛤仔(Ruditapes philippinarum),为摸清菲律宾蛤仔的生理活动与大叶藻的相互作用,2016年5~7月,在菲律宾蛤仔和大叶藻集中分布区,评估了菲律宾蛤仔种群资源量,现场流水法测定了菲律宾蛤仔个体水平的摄食、代谢生理,围隔实验法探讨了种群水平蛤仔与大叶藻的相互作用。结果显示,桑沟湾楮岛大叶藻床海区菲律宾蛤仔的平均生物量为(572.00±20.23) ind./m2,大(壳长为3.50~4.10 cm)、中(壳长为3.00~3.50 cm)、小(壳长为2.00~3.00 cm)规格各占9.01%、43.60%和47.38%。菲律宾蛤仔的排氨率、耗氧率、滤水率、摄食率分别为(0.44±0.15)~(1.40±0.35) μmol/(ind.·h)、(0.21±0.02)~(0.33± 0.08) mg/(ind.·h)、(0.69±0.38)~(0.83±0.66) L/(ind.·h)和(2.57±0.41)~(3.41±0.68) mg/(ind.·h),且都随体重的增加而增大。围隔实验设有3个实验组(蛤仔组、大叶藻组和大叶藻+蛤仔组),1个空白组,每组3个平行(大叶藻30茎枝左右、蛤仔15个左右),实验进行4 h。研究表明,蛤仔组、大叶藻+蛤仔组和大叶藻组间的溶氧浓度存在显著差异(P<0.05);蛤仔组与其他3组的氨氮浓度存在显著差异(P<0.05);蛤仔组、大叶藻+蛤仔组与空白组的水体颗粒物浓度存在显著差异(P<0.05),大叶藻组与空白组差异不显著(P>0.05)。桑沟湾楮岛海区菲律宾蛤仔养殖面积约为0.5 km2,蛤仔每天可以过滤46 t海水中的悬浮颗粒物,并为大叶藻提供0.4 t的氨氮。本研究为深入揭示大叶藻海区菲律宾蛤仔的生态作用提供了基础数据。     

胶州湾移植底播菲律宾蛤仔渔业生物学特性与养护对策研究

菲律宾蛤仔(Ruditapes philippinarum)属于软体动物门、双壳纲、帘形目、帘蛤科、蛤仔属,是我国主要的海产经济贝类之一,曾在胶州湾水域分布甚广。近年来由于自然种群资源严重衰退,目前主要以移植底播养殖为主。自2000年以来胶州湾底播养殖菲律宾蛤仔苗种主要来自福建莆田,菲律宾蛤仔的底播养殖已成为青岛的特色渔业。     

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.     

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.     

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.     

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.     

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.