饲料中添加锌对星斑川鲽幼鱼生长、生理生化指标和机体抗氧化的影响

以酪蛋白和明胶为蛋白源,以七水硫酸锌为锌源,在基础饲料中分别添加锌0、50、100、150、200、400mg/kg,配制成6种等氮等能的精制饲料,饱食投喂初始体重为62.89±0.51g的星斑川鲽幼鱼66d,探讨饲料锌水平对星斑川鲽幼鱼生长、血液生理生化指标和机体抗氧化功能的影响.结果表明,添加150～400mg/kg饲料锌显著提高了星斑川鲽幼鱼的增重率(WGR)(P<0.05),且WGR的最大值及饲料系数(FCR)的最小值均出现在150mg/kg锌饲料组.添加100～200mg/kg饲料锌显著提高了试验鱼血液红细胞数量(P<0.05),0mg/kg锌饲料组的血细胞比容和血红蛋白含量均显著低于其他各组(P<0.05).血清蛋白含量不受饲料锌添加量的影响(P>0.05).血清溶菌酶(LSZ)活力随着锌添加量的增加而显著升高(P<0.05),在锌添加量为150mg/kg时达最高值;当添加量高于150mg/kg时,LSZ活力变化不显著(P>0.05).0与50mg/kg锌饲料组的血清铜锌-超氧化物歧化酶(CuZn-SOD)活力显著低于其他各组(P<0.05).0和50mg/kg锌饲料组肌肉丙二醛(MDA)含量显著高于其他各组(P<0.05),以150mg/kg锌饲料组最低(P<0.05).建议星斑川鲽幼鱼精制饲料中锌的适宜添加量为150mg/kg.     

军曹鱼幼鱼日粮锌最适添加量的研究

在以卵白蛋白为蛋白源的基础饲料（Zn含量为5．65mg／kg）中添加10、20、30、40、50mg／kg以ZnSO4为Zn源的Zn，使饲料中总Zn含量为15．97、25．66、33．90、45．85、55．88mg／kg。投喂军曹鱼幼鱼8周。试验结果表明，基础饲料组鱼出现生长不良、厌食、皮肤糜烂和白内障等症状，其成活率、增重率、血清碱性磷酸酶活性（AKP）显著低于添加Zn组（P〈0．05），骨骼、肌肉、血清和肝脏Zn含量也表现出相同趋势。10mg／kg和20mg／kgZn添加量组鱼仍出现缺Zn症状，各项测定指标随Zn添加量的增加而增大。当饲料中Zn添加量达到30mg／kg时，各项指标趋向稳定，与添加量40mg／kg和50mg／kg组无显著差异。以增重率和骨骼Zn含量为主要评价指标，通过回归分析表明，以ZnSO4为Zn源时，军曹鱼幼鱼日粮Zn的最适添加量为42．86mg／kg。     

丙氨酰—谷氨酰胺和维生素E对军曹鱼的影响

本研究探讨了添加不同剂量和比例的丙氨酰—谷氨酰胺和维生素E对军曹鱼幼鱼相对质量增加率、特定生长率和不同组织器官RNA/DNA比值的影响。在饲料中添加不同剂量和比例的丙氨酰—谷氨酰胺和/或维生素E,饲喂军曹鱼幼鱼12周后,称其体质量,计算相对质量增加率和特定生长率,测定肝脏、肌肉、脑、心脏、肾和血清的RNA和DNA含量,计算RNA/DNA比值。将鱼特定生长率与各组织器官RNA/DNA比值做线性回归方程分析,比较二者的相关性。结果显示,添加丙氨酰—谷氨酰胺、维生素E可促进幼鱼的特定生长率。试验鱼主要组织器官RNA/DNA比值与特定生长率的线性回归相关系数r2的大小为肌肉血清肝脏肾心脏脑。其中鱼肉RNA/DNA比值与其特定生长率的线性回归相关系数r2=0.8422,血清RNA/DNA比值与特定生长率的线性回归相关系数r2=0.82705,均呈高度正相关。由此得出结论,在本试验条件下,添加丙氨酰—谷氨酰胺和/或维生素E可促进军曹鱼幼鱼的相对质量增加率和特定生长率,也增加其主要组织器官RNA/DNA比值;当每千克干饲料添加丙氨酰—谷氨酰胺5g和维生素E 50IU时,效果最佳。军曹鱼幼鱼的特定生长率与其肌肉、血清的RNA/DNA比值高度正相关,可互为指示。     

大口黑鲈幼鱼对饲料中锌的需求量

为确定大口黑鲈幼鱼对饲料锌的适宜需求量,以酪蛋白、明胶和鱼粉为主要蛋白质源,以ZnSO_4·H_2O为锌源制作半精制基础饲料,分别向基础饲料中添加0、25、50、100和200 mg/kg锌,制成5种含不同锌水平饲料(24.8、48.8、78.9、126.1和223.6 mg/kg干物质)(命名为Zn-25、Zn-49、Zn-79、Zn-126和Zn-224),投喂初始体质量为(10.99±0.07) g的大口黑鲈幼鱼8周。结果显示,饲料中补充25 mg/kg锌(Zn-49)显著提高了大口黑鲈增重率,降低了饲料系数,进一步提高锌的添加量后,各组增重率和饲料系数趋于稳定。当饲料锌含量为25～49 mg/kg时,T-SOD和CuZn-SOD活性增加,锌含量达到49 mg/kg后,其活性保持基本稳定,而AKP活性在Zn-79组最高。大口黑鲈全鱼和脊椎骨中的锌含量随饲料中锌含量的增加而上升,当饲料锌含量达到126 mg/kg (Zn-126)后,全鱼和脊椎骨中的锌含量不再显著增加,而全鱼铁、骨铁、骨锰含量和全鱼铁、锌沉积率则随饲料锌含量的增加而下降。研究表明,在半精制饲料中补充锌可以显著改善大口黑鲈的生长和饲料利用,提高血清免疫能力、全鱼锌和骨锌的沉积,以增重率、饲料系数、全鱼锌和骨锌为指标,基于折线模型确定大口黑鲈幼鱼对饲料中锌的需求量分别为45.5、44.6、121.8和130.5 mg/kg干物质。     

饲料中添加叔丁基氢醌对大菱鲆生长、血液生化指标、非特异性免疫及肠道组织结构的影响

为研究饲料中添加不同含量叔丁基氢醌(TBHQ)对大菱鲆幼鱼生长、血液生化指标、非特异性免疫及肠道组织结构的影响,在饲料中分别添加0、150、450和750 mg/kg的叔丁基氢醌,配制成4种等氮等脂实验饲料,选择初始体质量(8.31±0.04)g大菱鲆幼鱼,随机分成4组,每组6个重复,每个重复30尾,采用饱饲投喂方式,每天投喂2次,饲养周期为12 W。结果显示,与对照组相比,450和750 mg/kg TBHQ添加组大菱鲆的增重率、特定生长率均显著降低;450 mg/kg TBHQ添加组实验鱼血清碱性磷酸酶活力显著高于150 mg/kg TBHQ添加组;150 mg/kg TBHQ添加组实验鱼血清白蛋白和高密度脂蛋白含量显著低于对照组和450 mg/kg添加组;450 mg/kg TBHQ添加组鱼的血清肌酐含量显著高于对照组;150 mg/kg TBHQ添加组鱼的血清总蛋白含量显著低于对照组;饲料中添加高剂量的TBHQ能够显著升高血清中CAT、溶菌酶活力(450和750 mg/kg)及头肾吞噬细胞呼吸爆发活力(750 mg/kg);饲料中TBHQ添加量为750 mg/kg时,血清SOD活力显著降低;与对照组相比,饲料中添加450和750 mg/kg TBHQ能够显著降低中肠肠道绒毛长度与肠道直径比,而添加750 mg/kg TBHQ时中肠肠道做绒毛长度与肠道直径的比值显著降低。研究表明,饲料中TBHQ的添加量为150 mg/kg时,对大菱鲆幼鱼生长及生理生化指标无显著影响,而饲料中添加450 mg/kg以上的TBHQ则会对大菱鲆幼鱼的生长及生理状况产生一定负面作用。     

饲料中不同维生素E添加量对黄颡鱼幼鱼生长性能及免疫功能的影响

本研究探讨了饲料中不同维生素E添加量对黄颡鱼(Pelteobagrus fulvidraco)幼鱼生长和免疫的影响。在以鱼粉、豆粕为蛋白源的基础饲料中分别添加0mg/kg(对照组)、25mg/kg、75mg/kg、125mg/kg和175mg/kg的维生素E配成5种实验饲料。在水温(24.0±3.0)℃下,用上述实验饲料分别饲喂平均体质量约为5.1g的黄颡鱼幼鱼50d。实验结果表明,饲料中维生素E的添加量对黄颡鱼的特定生长率和饲料效率的影响不显著(P0.05);而添加量为175mg/kg时,黄颡鱼摄食率显著降低(P0.05);随着饲料中维生素E添加量的增高,黄颡鱼血浆超氧化物歧化酶(SOD)的活性未产生显著变化(P0.05);添加量为125mg/kg和175mg/kg时,血浆中丙二醛(MDA)的含量显著降低(P0.05);白细胞吞噬指数随添加量升高显著上升(P0.05),而吞噬百分率没有显著变化(P0.05)。综合以上结果,饲料中添加适量的维生素E可适当改善黄颡鱼的摄食,增强黄颡鱼的非特异性免疫力和抗氧化能力,从而提高动物的健康状况。推荐在黄颡鱼幼鱼饲料中添加125mg/kg的维生素E。     

吉富罗非鱼对饲料中锌的需要量

为考察吉富罗非鱼(GIFT,Oreochromis niloticus)对饲料中锌的需要量,以蛋氨酸锌为锌源,配制锌添加水平分别为0,10,20,40,80,160 mg/kg的6组等氮等脂饲料(实测值分别为9.98,21.47,33.75,56.03,88.16,172.54 mg/kg),饲喂初始体质量为(84.44±3.04)g的吉富罗非鱼,试验鱼分为6组,每组3个重复,每个重复20尾鱼,养殖周期为10周。结果显示,随着饲料中锌含量的增加,吉富罗非鱼的增重率、特定生长率先显著升高,在锌含量达到33.75 mg/kg后趋于稳定,添加锌显著降低了饲料系数,提高了成活率。饲料锌含量对全鱼水分、粗蛋白及灰分含量无显著影响,显著降低了全鱼粗脂肪含量。饲料中添加锌对血清总胆固醇含量无影响,显著提高了血清碱性磷酸酶的活性,碱性磷酸酶活性在锌含量达到33.75 mg/kg后趋于稳定,血清甘油三酯含量,乳酸脱氢酶、谷草转氨酶和谷丙转氨酶活性则呈下降趋势。饲料锌含量显著影响脊椎骨、全鱼和肝脏锌的含量,脊椎骨和全鱼锌含量先线性上升,在锌含量达到56.03 mg/kg后趋于稳定,各组的肌肉锌含量无显著差异。以增重率、骨骼锌和全鱼锌含量为评价指标,根据折线回归分析得出,以蛋氨酸锌为添加锌源,吉富罗非鱼对饲料中锌的需要量分别为32.37、55.67和56.13 mg/kg。     

肌醇对胭脂鱼生长、体成分和部分血清生化指标的影响

以酪蛋白、明胶和鱼粉为蛋白源配制6组实验饲料,分别在饲料中添加0、75、150、300、600和1 200mg/kg的肌醇,每组设3个重复,连续投喂初始体质量(10.01±0.24)g的胭脂鱼(Myxocyprinus asiaticus)幼鱼8周,考察饲料中添加不同水平的肌醇对胭脂鱼幼鱼生长性能、全鱼以及肌肉营养成分和部分血清生化指标的影响,以确定胭脂鱼幼鱼饲料中肌醇的适宜添加量。结果显示:随着饲料中肌醇含量增加,胭脂鱼幼鱼增重率、成活率和特定生长率呈先上升后稳定的趋势,均在300 mg/kg组时达到稳定;饲料肌醇对全鱼体成分无显著性影响,肌肉脂肪含量在300 mg/kg组时显著低于未添加组;饲料中肌醇对血清总胆固醇、低密度脂蛋白胆固醇和血清甘油三酯均有显著性影响;饲料中肌醇(150 mg/kg)不足时,血清中谷草转氨酶和谷丙转氨酶的活性显著高于其它实验组。以特定生长率为评价指标,经折线回归分析,饲料中补充310.3 mg/kg的肌醇时,胭脂鱼幼鱼获得最大生长。     

饲料中铁元素含量对鱼菜共生系统水质及鱼菜生长的影响

通过控制饲料中铁元素含量,研究其对鱼(金鲫)、菜(红皱生菜和红油阿拉斯)生长和系统水质的影响。实验设置1个对照组和5个处理组,饲料铁含量分别为0、0、10、20、40和80 mg/kg。结果显示:该系统对水体质量有净化作用;不同铁含量对金鲫存活率影响不显著(P0.05),对增重率影响显著(P0.05);当饲料中铁含量为20 mg/kg时,金鲫鱼存活率和鱼体增重率均达到最大值;饲料中铁含量为80 mg/kg时,金鲫的存活率和增重率均出现下降趋势;饲料中不同铁含量对两种蔬菜的存活率和增重率均没有产生显著影响(P0.05),但在增重率方面有一定的差异。研究表明:饲料中添加铁元素能够促进金鲫和蔬菜的生长,当铁元素含量为20 mg/kg时,该鱼菜共生系统具有最佳的生产力。     

饲料中添加蛋氨酸锌对奥尼罗非鱼幼鱼生长和抗氧化功能的影响

以奥尼罗非鱼(Oreochromis aureus×Oreochromis niloticus)幼鱼为试验对象,以蛋氨酸锌为饲料锌源,研究了在饲料中添加6种浓度的锌(0、5、10、20、40和80 mg/kg)对奥尼罗非鱼幼鱼生长和肌肉抗氧化功能的影响。试验周期56d。试验结果显示:饲料转化率、全鱼脂肪含量、肝脏中水分和脂肪含量随锌添加浓度的升高而降低;增重率、特定生长率、脊椎骨中锌离子含量和血液红细胞数量在锌添加浓度为10 mg/kg时达到最大值;肌肉中硫代巴比妥酸底物(TBARS)值在锌添加浓度为5 mg/kg时达到最小值。饲料中锌添加浓度为5~10 mg/kg时,奥尼罗非鱼幼鱼生长迅速,鱼体抗氧化功能增强。     

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.