Assessment of dietary lecithin and cholesterol requirements of mud crab, Scylla serrata, megalopa using semi-purified microbound diets

The effects of varying dietary lecithin and cholesterol levels on growth, development and survival of mud crab, Scylla serrata, megalopa were evaluated using six semi‐purified, microbound diets formulated to be iso‐energetic and containing three levels of supplemental lecithin (0, 20 and 40 g kg⁻¹ diet dry weight) and two levels of supplemental cholesterol (0 and 7 g kg⁻¹ diet dry weight). Fifteen megalopa were reared individually in each treatment and the nutritional value of diets was assessed on basis of mean dry weight and mean carapace width of newly settled first crab stage, as well as development time to the first crab stage and overall survival. A significant interaction between supplemental dietary lecithin and supplemental dietary cholesterol was found for final mean dry weight of newly settled crabs, and highest survival (60%) was recorded for megalopa fed diets containing the highest levels of dietary lecithin (39.7–44.1 g kg⁻¹) (diet 5 and 6) regardless of whether diets were supplemented with cholesterol; this rate of survival was identical to that of megalopa fed live Artemia nauplii. The results indicate that supplemental dietary cholesterol may not be essential for mud crab megalopa when fed diets containing sufficient levels of supplemental dietary phospholipids.     

Development of nursery culture techniques for the mud crab Scylla paramamosain (Estampador)

Cannibalism is one of the main causes of mortality in the culture of the mud crab Scylla paramamosain, particularly in the early post‐larval and juvenile stages when the densities of hatchery‐reared crabs may be very high before stocking into ponds or release into the wild for stock enhancement. In a series of experiments investigating cannibalism mitigation, the influence of stocking density, the effectiveness of sand substrate, brick and shell shelters and feed type were compared in culture of crabs from instar 1 for short nursery periods of 15–30 days. Inclusion of brick and shell shelters significantly increased survival over sand substrate alone. However, inclusion of shelters did not affect growth rates. In scaled‐up nursery production in lined‐ponds, with shelters, live Artemia biomass and fresh chopped shrimp or tilapia were found to be equally effective feeds for juvenile crabs stocked at a density of 70 m⁻² from instar 1 and grown for 30 days [52–66% survival, 21.6–24.6 mm carapace width (CW)]. In an extended nursery period for a further 30 days, crabs of 22 mm CW, stocked at 30 m⁻² in the same ponds, attained a final size of 34.5–36.2 mm CW with a survival of 64.3–67.0% using the same feeds.     

锯缘青蟹促雄腺发育的组织学研究

采用组织切片技术，以OlympusBH-2型显微镜对锯缘青蟹(Scylla serrata)促雄腺的发育进行观察。结果显示，促雄腺附着于射精管近末端，发育过程可分为4期：Ⅰ期促雄腺短小，腺细胞数量少；Ⅱ期促雄腺呈明显的索状；Ⅲ期促雄腺体积达到最大，一些部位膨大增生；Ⅳ期促雄腺不再生长，腺体急剧退化。腺细胞具有2种类型：A型细胞，核圆、异染色质少、胞质染色浅；B型细胞，核扁平、异染色质多，细胞染色深、界限不清晰，有时细胞质消失。促雄腺发育过程中，A、B型细胞数量、比例发生变化。B型细胞为A型细胞完成分泌后的存在形式，B型细胞比例反映了促雄腺分泌活动的状况。锯缘青蟹促雄腺发育和精巢成熟具有一定的相关性。     

锯缘青蟹亲蟹选择及培育技术

亲蟹质量及亲蟹培育是锯缘青蟹人工育苗的基础。本文就亲蟹的选择、亲蟹暂养期的环境、亲蟹的饵料及饲养条件进行了探讨。在相同的理化因子条件下,海捕亲蟹的抱卵率(62.13％)大约为养殖亲蟹抱卵率(26.67％)的2.31倍。     

饥饿对拟穴青蟹大眼幼体和Ⅰ期仔蟹蜕皮和生长的影响#br#

为了给拟穴青蟹(Scylla paramamosain)苗种培育过程中饵料的合理投喂提供基础理论数据,采用投喂-饥饿和饥饿-投喂的处理方式对拟穴青蟹大眼幼体和Ⅰ期仔蟹分别开展营养储存饱和点实验(PRS)和不可恢复点实验(PNR),研究饥饿对大眼幼体和Ⅰ期仔蟹蜕皮和生长的影响。结果显示,大眼幼体的PRS实验中,投喂时间≤2 d时,大眼幼体的蜕皮率为0;投喂时间≥4 d时,大眼幼体的蜕皮率和发育时间与连续投喂组(F组)无显著性差异;但投喂4 d-饥饿组(F4S组)大眼幼体蜕皮后Ⅰ期仔蟹的增重率和个体大小均显著小于F组(P<0.05)。大眼幼体的PNR实验中,饥饿2 d时大眼幼体的存活率仅为(30.00±13.23)%。Ⅰ期仔蟹的PRS实验中,连续饥饿组(S组)Ⅰ期仔蟹的蜕皮率为0,而投喂2 d-饥饿组(F2S组)、投喂3 d-饥饿组(F3S组)和F组3组Ⅰ期仔蟹的蜕皮率均无显著性差异。投喂1 d-饥饿组(F1S组)和F2S组Ⅰ期仔蟹蜕皮后Ⅱ期仔蟹的增重率和个体大小均显著小于F组(P<0.05),且F1S组Ⅰ期仔蟹的发育时间显著延长(P<0.05)。Ⅰ期仔蟹的PNR实验中,除饥饿1 d-投喂组(S1F组)外,F组Ⅰ期仔蟹的蜕皮率显著高于其他处理组(P<0.05);各组Ⅰ期仔蟹蜕皮后Ⅱ期仔蟹的增重率与饥饿时间呈负相关,而发育时间却与饥饿时间呈正相关;饥饿时间≥2 d时,Ⅰ期仔蟹蜕皮后Ⅱ期仔蟹的个体大小明显变小。拟合分析结果显示,大眼幼体的PRS;值是3.57 d,Ⅰ期仔蟹的PRS;和PNR;值分别是0.90 d和2.01 d。研究结果表明,新蜕皮的大眼幼体必须给予充足的饵料才可确保高的存活率,大眼幼体投喂6 d后可以适当减少投喂量,短期饥饿对Ⅰ期仔蟹蜕壳和生长的影响相对较小,Ⅰ期仔蟹的耐饥饿能力强于大眼幼体。     

锯缘青蟹苗池微生态环境影响因素的初步探讨

通过对锯缘青蟹苗池微生态环境和水质环境的全过程检测,探讨了总菌数、弧菌数及弧菌数/总菌数的消长规律,并对苗种培育阶段涉及的各种外源因素及控制苗池微生态环境的相关手段的有效性作了初步的探讨。结果表明:苗池水体中总菌数在Z1~Z2少量添加水不换水阶段,呈相对稳定状态,进入Z3后总菌数逐渐增加,最高达3.5×106cfu/m l;弧菌数在Z1培育阶段出现2×102cfu/m l激增至5×104cfu/m l的峰值,第二峰值出现在Z5阶段,达6×105cfu/m l;弧菌数/总菌数比值在育苗起始时仅为0.4%,之后迅速升至30%~40%,在Z5阶段,由于弧菌数量急剧上升,达到50%的高比值;NH4-N与COD检测值在育苗过程中变动较大,两者与弧菌数/总菌数比值呈正相关关系。现行育苗方式中对苗池微生态环境产生影响的主要因素是苗种培育密度,海水、饵料的处理方式和抗生素;净化功能菌和蛭弧菌应用于育苗水体具有抑制弧菌繁殖的效果。     

锯缘青蟹大眼幼体与凡纳滨对虾混养试验

利用3口池塘共1.14 hm2进行锯缘青蟹大眼幼体与凡纳滨对虾的混养试验,投放锯缘青蟹大眼幼体8500只,凡纳滨对虾苗2.03×105尾,经96~129 d的养殖,收获锯缘青蟹729.1 kg,凡纳滨对虾2804.3 kg;锯缘青蟹平均312 g/只,凡纳滨对虾57.5尾/kg;锯缘青蟹大眼幼体成活率27.5%,凡纳滨对虾成活率79.4%。试验结果表明,锯缘青蟹大眼幼体可以直接投入池塘中与凡纳滨对虾混养,将为今后大规模发展锯缘青蟹养殖摸索出一条有效途径。     

锯缘青蟹卵巢发育的组织学观察

根据锯缘青蟹卵巢的外部形态和内部组织学特征,卵巢发育可以划分为六个时期:未发育期、发育早期、发育期、将成熟期、成熟期和排卵后期。在发育早期,多数卵母细胞胞质中有多个嗜酸性液泡,这种结构在其他十足类卵母细胞中较少见。少数个体在发育早期发生卵母细胞全面退化,这种现象可能是缺乏交配或饥饿造成的。     

Lipids and fatty acids in wild and pond-reared mud crab Scylla serrata (Forsskål) during ovarian maturation and spawning

Wild‐caught and pond‐reared female mud crab Scylla serrata at different stages of ovarian maturation were collected from Samar and Capiz, Philippines. Crabs were categorized into five stages according to the external morphological and microscopic appearance of the most advanced oocytes. The ovaries, hepatopancreas, muscle and newly spawned eggs (NSE) were analysed for lipid class components and fatty acids. Total lipid was higher in pond‐reared than in wild‐caught crabs but increased with ovarian maturation in both groups. Ovarian lipid peaked at the fully mature stage, coinciding with a decline in hepatopancreatic and muscle lipids. Lipid levels declined significantly in spent females. The tissues contained elevated highly unsaturated fatty acids such as arachidonic (20:4n‐6), eicosapentaenoic (20:5n‐3) and docosahexaenoic (22:6n‐3) acids, but at higher levels in late maturing and fully mature ovaries and in NSE. The type of lipid class and fatty acid components in mature ovaries as well as in NSE are generally considered to be indicative of their importance in reproductive physiology and embryonic and larval development.     

青蟹的营养需求研究及其配合饲料研制

青蟹属（Scylla）有锯缘青蟹（Scylla serrata），拟穴青蟹（S．paramamosain），紫螯青蟹（S．tranquebarica）和榄绿青蟹（S．olivacea）等4个种。我国以拟穴青蟹占绝对优势，它有个体大、生长快、适应性强、肉味鲜美、营养丰富等特点，已成为具有重要经济价值的海水养殖蟹类之一。