吉富罗非鱼对饲料中苯丙氨酸的需要量

分别用含6种水平(质量比分别为0.78%、0.95%、1.09%、1.34%、1.51%和1.72%)苯丙氨酸(phenylalanine,Phe)的等氮等能(粗蛋白30.10%,总能17.73 MJ/kg)饲料,在池塘网箱中(实验期间水温为24~32℃)饲喂初始体重为(52.70±1.80)g的吉富罗非鱼60 d,考察饲料Phe对吉富罗非鱼(GIFT,Oreochromis niloticus)生长性能、饲料系数、体成分、部分血清生化指标及前肠消化酶活性的影响,以期获得吉富罗非鱼对饲料苯丙氨酸的需要量。结果表明,随着饲料中Phe水平的升高,吉富罗非鱼的增重率、特定生长率、蛋白质效率、蛋白质沉积率、肥满度、肝体比和脏体比均呈现先上升后下降的趋势,饲料系数呈现先下降后上升的趋势;全鱼粗脂肪和全鱼灰分含量显著上升(P0.05),肌肉灰分含量显著下降(P0.05)。饲料中Phe对全鱼水分和粗蛋白质、肌肉水分、肌肉粗蛋白质和肌肉粗脂肪含量无显著性影响(P0.05);各实验组的肌肉氨基酸含量差异不显著(P0.05)。饲料中Phe显著影响血清中谷丙转氨酶活性,甘油三酯、总胆固醇和葡萄糖的含量(P0.05),对谷草转氨酶活性无显著性影响(P0.05);Phe显著影响肠蛋白酶、肠脂肪酶和肠Na~+-K~+-ATP酶活性(P0.05),而对肠淀粉酶活性影响不显著(P0.05)。以增重率、饲料系数和蛋白质效率为评价指标,通过二次回归分析可知,吉富罗非鱼对饲料中Phe需要量为1.17%~1.21%,占饲料蛋白质的3.89%~4.02%。本研究结果为合理配制吉富罗非鱼配合饲料提供了理论依据。     

蝇蛆粉替代鱼粉对罗非鱼生长、肌肉组成和肝脏非特异性免疫指标的影响

为探讨以蝇蛆粉替代鱼粉对吉富罗非鱼生长性能、肌肉组成和肝脏非特异性免疫指标的影响,将450尾初始体质量为(80.26±7.36)g的吉富罗非鱼随机分为6组,每组3个平行,进行了饲养对比试验。试验组分别用蝇蛆粉替代基础饲料中20 %、40 %、60 %、80 %和100 %的鱼粉,对照组投喂基础饲料,养殖周期60 d。试验结果,以蝇蛆粉替代鱼粉,各替代水平组试验鱼的终末体质量、增重率、特定生长率、肥满度、成活率、饲料系数、肌肉中粗蛋白、水分含量、肝脏丙二醛含量无显著差异(P＞0.05)。除20 %替代组外,其它各试验组鱼的肝体比、脏体比与对照组相比显著降低(P＜0.05)。随着蝇蛆粉替代水平的增加,罗非鱼肌肉中粗灰分、总磷的含量显著降低(P＜0.05)。替代水平不超过40 %时,各替代组试验鱼肌肉中粗脂肪、钙及肝脏超氧化歧化酶的含量无显著差异(P＞0.05)；当替代水平不小于60 %时,试验鱼肌肉中粗脂肪、钙的含量显著降低(P＜0.05),但肝脏超氧化歧化酶含量显著升高(P＜0.05)。结果表明,在本试验条件下,以生长性能、肌肉成分和肝脏非特异性免疫作为评价指标,蝇蛆粉可完全替代罗非鱼饲料中的鱼粉。     

吉富罗非鱼对饲料中维生素B1的需要量

采用维生素B1(VB1)含量为0.08(对照组)、0.57、1.13、2.09、4.11和8.09 mg/kg的6种纯化饲料,分别饲养初始体质量为(64.4±1.5)g的吉富罗非鱼12周,研究VB1对其生长性能、部分血清生化指标、肝脏VB1蓄积量及转酮醇酶基因表达量的影响,以确定其对饲料VB1的需要量.结果显示,随着饲料中VB1含量增加,吉富罗非鱼增重率先呈线性增加后趋于稳定,当饲料中VB1含量为1.13、2.09、4.11、8.09 mg/kg时增重率达最大.吉富罗非鱼肝脏VB1含量随着饲料VB1含量增加不断增大,当增加到2.09 mg/kg后趋于稳定.饲料中缺乏VB1显著提高血清丙酮酸含量(P＜0.05),但对全鱼水分、粗脂肪、粗蛋白、灰分无显著性影响(P＞0.05).饲料中添加VB1显著提高血清高密度脂蛋白胆固醇和肝脏转酮醇酶基因表达量(P＜0.05).饲料中VB1含量大于1.13 mg/kg各组的肝脏转酮醇酶活性显著高于VB1含量小于0.57 mg/kg组(P＜0.05).折线回归分析表明,吉富罗非鱼(64 ～325 g)获得最佳生长时对饲料VB1需要量为1.16 mg/kg;肝脏VB1蓄积量达到最大时,对VB1的需要量为2.06mg/kg.     

吉富罗非鱼对饲料亚油酸的需要量

选用初始体重为(60.98±3.82)g的吉富罗非鱼(Oreochromis niloticus)630尾,随机分成7组(每组设3个重复,每个重复30尾),饲喂亚油酸含量分别为0.07%(对照组)、0.36%、0.61%、1.03%、2.00%、3.00%和4.15%的7种半纯化等能等氮饲料10周。结果表明,鱼体增重率、饲料效率、蛋白质效率和蛋白质沉积率均在亚油酸水平为1.03%时较对照组差异显著(P0.05),且均在饲料亚油酸水平为2.00%时达到最大。经二次回归分析,饲料亚油酸水平为2.49%和2.66%时吉富罗非鱼分别获得最大增重率和最高饲料效率。通过折线回归发现饲料亚油酸水平为1.02%时,吉富罗非鱼获得最大蛋白沉积。肝体比和脏体比均随亚油酸水平的升高而升高,当饲料亚油酸含量为0.61%~4.15%时显著高于对照组(P0.05)。亚油酸添加组的肌肉粗脂肪含量显著高于对照组(P0.05);当饲料亚油酸含量为1.03%~4.15%时,肝和全鱼粗脂肪含量显著高于对照组(P0.05)。随饲料亚油酸水平升高,血清甘油三酯和总胆固醇变化趋势一致,呈现先下降后上升的趋势,经二次回归分析亚油酸水平为1.63%时血清甘油三酯含量最低;各亚油酸添加组的血清高密度脂蛋白胆固醇含量显著高于对照组,且在饲料亚油酸含量为1.13%时达到最大(P0.05);当饲料亚油酸水平为1.03%~4.15%时,血清低密度脂蛋白胆固醇含量显著低于对照组(P0.05)。随饲料中饱和脂肪酸(∑SFA)含量下降,吉富罗非鱼肌肉和肝脏∑SFA含量均呈下降的趋势;随饲料亚油酸水平增加,肌肉和肝脏的n-6多不饱和脂肪酸(∑n-6 PUFA)含量呈上升趋势,肌肉和肝脏的∑n-3 PUFA含量呈下降趋势。综上所述,初始体重为(60.98±3.82)g的吉富罗非鱼饲料亚油酸需要量为1.02%~2.66%。     

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。     

34 ℃水温下吉富罗非鱼对饲料脂肪的需求量

为研究34 ℃水温下吉富罗非鱼对饲料脂肪的需求量，选用初始体质量为(50.88±1.57) g的吉富罗非鱼360尾，随机分成6组(每组设3个重复，每重复20尾)，饲喂脂肪含量分别为0.22%(对照组)、2.83%、4.98%、7.45%、9.23%和12.47%的6种纯化饲料，在34 ℃水温下饲养56 d后，测定并分析了吉富罗非鱼的生长性能、体成分、部分血清生化和肝脏脂肪代谢酶活性等指标。结果显示，随饲料脂肪水平升高，吉富罗非鱼增重率、特定生长率、蛋白质效率与蛋白质保留率均呈现先上升后下降的趋势，饲料系数和摄食率呈现相反的趋势；12.47%实验组肝体比显著高于其他实验组，其他指标组间无显著性差异。饲料脂肪水平对吉富罗非鱼的成活率无显著影响。对照组全鱼粗脂肪含量显著低于其他实验组；当饲料脂肪含量为7.45%~12.47%时，肌肉粗脂肪含量显著高于对照组；肝脏粗脂肪含量在饲料脂肪含量为2.83%~9.23%时较对照组显著降低。血清甘油三酯和总胆固醇随饲料脂肪水平升高呈现先下降后上升的趋势；肝脏脂肪酶和脂蛋白酯酶活性随脂肪水平的增加呈上升趋势，在12.47%组达到最大值；肝脂酶的活性呈先上升再下降最后趋于稳定的趋势，在脂肪水平为2.83%时最高, 显著高于其他各组。经回归分析，在34 ℃水温下，吉富罗非鱼要获得最佳的增重率、蛋白质效率和最低饲料系数对饲料脂肪的需求量分别为4.92%、5.67%和6.49%。     

饲料碳水化合物与脂肪比例对吉富罗非鱼成鱼生长、体成分和血清生化指标的影响

为确定吉富罗非鱼(GIFT Oreochromis niloticus)成鱼饲料中适宜的碳水化合物与脂肪比例(C/L),实验设计了6组等氮等能的半纯化饲料,饲料C/L比例分别为1.53、2.36、3.55、5.58、9.85、21.82。投喂初始质量为(218.33±11.03) g的吉富罗非鱼成鱼56 d。结果显示,增重率和特定生长率在C/L比例为3.55时最高,显著高于C/L比例1.53、9.85和21.82组(P0.05);饲料效率和蛋白质效率在C/L比例介于2.36～5.58时无显著差异,显著高于1.53和21.82组(P0.05)。随着饲料C/L比例的升高,肝体比和脏体比呈显著下降趋势(P0.05),成活率各组无显著差异(P0.05)。全鱼和肝脏的粗脂肪含量随饲料C/L比例的增加显著降低(P0.05)。血清甘油三酯(TG)和高密度脂蛋白胆固醇(HDL-C)含量随C/L比例升高而下降,低密度脂蛋白胆固醇(LDL-C)和血糖(GLU)含量则呈显著上升趋势(P0.05)。分别利用二次多项式回归分析增重率、蛋白质效率和饲料效率与碳水化合物水平及脂肪水平的相关性,得到饲料中适宜的C/L比例分别是4.19、4.15和4.11。研究表明吉富罗非鱼成鱼饲料中适宜的C/L比例为4.11～4.19。     

不同种类碳水化合物对吉富罗非鱼生长性能、体组成和血清生化指标的影响

为了解罗非鱼对不同种类碳水化合物(CBH)的利用效果,研究了6种碳水化合物对罗非鱼生长性能、体组成和血清生化指标的影响。实验选用720尾初重为(3.0±0.3)g的健康吉富罗非鱼,随机分为6组,每组4个重复,每个重复30尾,分别投喂设计含30%南方糙米、次粉、玉米淀粉、马铃薯淀粉、甘薯淀粉和木薯淀粉的6种不同CBH的等氮、等能饲料,实验周期为8周。结果显示,南方糙米、玉米淀粉组的终末均重、增重率、特定生长率和蛋白效率显著高于其他组,而饲料系数明显最低(P0.05)。CBH种类明显影响全鱼、肌肉的组成(P0.05)。玉米淀粉组肝糖原含量明显高于马铃薯淀粉、甘薯淀粉和木薯淀粉组(P0.05),而马铃薯淀粉和甘薯淀粉组的血糖明显低于木薯淀粉、玉米淀粉和次粉组(P0.05)。CBH种类对血清CHO、TG影响明显(P0.05),但对TP、SOD、T-AOC和MDA的影响不明显(P0.05)。研究表明,不同种类CBH对罗非鱼生长性能的影响明显(P0.05),以特定生长率为指标,罗非鱼对南方糙米和玉米淀粉的利用效果较好。     

饲料蛋白质和能量含量对云纹龙胆石斑鱼幼鱼生长、体组成及消化酶活力的影响

为探求云纹龙胆石斑鱼(Epinephelus lanceolatus♂×E.moara♀)幼鱼饲料的最适蛋白质和能量含量,以鱼粉和大豆浓缩蛋白为蛋白源、添加鱼油构建能量梯度,配制粗蛋白含量为46%、50%和54%,能量含量为20.00、20.50和21.00 k J/g,蛋能比为22.04~26.87 mg/k J的9组饲料,编号为D1~D9组,投喂初始体重为(46.23±0.51)g的云纹龙胆石斑鱼幼鱼56 d。结果显示,蛋白质和能量的交互作用对云纹龙胆石斑鱼幼鱼增重率影响显著(P0.05),蛋白质和能量升高显著提高增重率和特定生长率(P0.05)。蛋白质和能量的交互作用对蛋白质沉积率和肝体比影响显著(P0.05),蛋白质升高显著提高能量保留率和肥满度(P0.05),蛋白质效率先升后降(P0.05);能量升高显著提高蛋白质效率和能量保留率(P0.05);D6组蛋白质沉积率和蛋白质效率显著高于其他组(P0.05)。蛋白质和能量的交互作用对全鱼及肌肉水分、粗蛋白、粗灰分均无显著影响(P0.05),全鱼及肌肉粗蛋白随饲料粗蛋白升高而升高(P0.05),水分随能量升高而降低(P0.05),全鱼粗脂肪随蛋能比降低而升高(P0.05)。蛋白质和能量的交互作用对胰蛋白酶、脂肪酶和淀粉酶活力影响显著(P0.05),胃蛋白酶活力随蛋白质含量升高而升高(P0.05),能量对其无显著影响(P0.05);D6组胰蛋白酶活力最高,其随饲料蛋能比降低呈先升后降的趋势(P0.05),能量为21.00 k J/g时,脂肪酶活力显著高于其他组(P0.05)。综上,在设定的蛋白质和能量范围内云纹龙胆石斑鱼幼鱼饲料以50%粗蛋白,21.00 k J/g能量为宜。     

饲料中添加中性蛋白酶对吉富罗非鱼生长和消化功能的影响

在吉富罗非鱼(Oreochromis niloticus)基础饲料中添加中性蛋白酶,添加量分别为0.00%、0.05%、0.1%、0.15%、0.2%和0.25%,研究添加后对吉富罗非鱼生长和消化功能的影响。结果表明,在饲料中添加0.1%~0.25%的中性蛋白酶,吉富罗非鱼的相对增重率和特定生长率显著提高,饲料系数显著降低(P<0.05);添加0.1%~0.2%的中性蛋白酶,显著提高饲料干物质表观消化率和粗蛋白表观消化率(P<0.05);添加量为0.1%~0.15%时,肝胰脏蛋白酶显著高于对照组(P<0.05),添加量为0.15%时,肠道蛋白酶活性显著提高(P<0.05)。综合鱼体相对增重率、特定生长率、饲料系数、消化器官消化酶活性等各项指标,吉富罗非鱼饲料中中性蛋白酶的添加量以饲料的0.1%~0.2%为宜。     

Surface disinfection of Pacific threadfin, Polydactylus sexfilis, and amberjack, Seriola rivoliana, eggs

The effects of exposing the eggs of Pacific threadfin and amberjack eggs (AEs) to different concentrations of hydrogen peroxide for 5 min on hatch rate and survival were assessed in a series of experiments using a petri dish model rearing system. Despite significant inter‐batch variation in hatch rate, it was shown that eggs of both species could be safely exposed to up to 11 340 mg L⁻¹ H₂O₂ for 5 min. Exposure to 34 230 mg L⁻¹ H₂O₂ for 5 min was shown to be lethal to AEs at a late stage of development. In two further experiments, it was demonstrated that Pacific threadfin eggs were resistant to all tested concentrations of a range of polyvinylpyrrolidone iodine (PVP‐I) concentrations and contact times (up to 1000 mg L⁻¹ PVP‐I for 10 min). The level of bacteria adhering to the eggs of both species was highly variable. Where eggs were heavily colonized (>10⁴ cfu egg⁻¹), hydrogen peroxide concentrations of at least 11 340 mg L⁻¹, or PVP‐I concentrations higher than 500 mg L⁻¹ for 10 min, were required for effective sterilization. In less colonized batches, rinsing in sterile seawater or exposure to lower (550 mg L⁻¹) concentrations of H₂O₂ was sufficient to result in high apparent levels of surface sterility (<1 cfu egg⁻¹).     

Anguilla huangi Teng, Lin, and Tzeng, 2009, is a junior synonym of Anguilla luzonensis Watanabe, Aoyama, and Tsukamoto, 2009

Anguilla luzonensis and A. huangi were each described in 2009 using eels obtained from northern Luzon Island. We examined the taxonomic status of these two groups of eels using morphological and molecular genetic characters. There were no significant differences in two vertebrae counts between eels of A. luzonensis and A. huangi. Mitochondrial 16S ribosomal RNA and cytochrome b genes sequences were obtained and compared among 28 specimens of A. luzonensis, the holotypes of A. luzonensis and A. huangi, and one specimen of the other 15 anguillid species. The specimens of A. luzonensis exhibited almost identical sequences, including the holotype, with only a few site differences, and the genetic difference between the holotypes of A. luzonensis and A. huangi was within the range of differences of specimens of A. luzonensis. The other anguillid species were genetically very different from A. luzonensis and A. huangi, although A. interioris is a closely related species. It is clear that A. luzonensis and A. huangi are the same species, and according to the principle of priority in zoological nomenclature, A. luzonensis Watanabe, Aoyama, and Tsukamoto, 2009 is the valid species name, and A. huangi Teng, Lin, and Tzeng, 2009 is a junior synonym of A. luzonensis.     

驼背鲈(Chromileptes altivelis)的胚胎发育及仔、稚、幼鱼形态观察

对驼背鲈(Chromileptes altivelis)的胚胎发育及仔、稚、幼鱼的形态特征进行了详细的观察与研究,描述了从受精卵到仔、稚、幼鱼各发育期的时间和形态特征变化。结果表明,在水温25-26℃、盐度30的海水中,受精卵历时27 h 25 min完成整个胚胎发育过程,经历从卵裂、囊胚、原肠、神经胚到肌节形成、各器官的逐渐形成、变化、完善等一系列的胚胎发育和变化过程;根据其卵黄囊消长情况、鳞片的覆盖状态、体色发生的不同变化以及第二背鳍和腹鳍的消长,将胚后发育分为仔、稚、幼鱼3个阶段。在水温22-26℃、盐度29-31、DO≥5 mg/L的条件下,2-3 d仔鱼卵黄囊消失,开口摄食;生长发育至31 d,仔鱼已变态进入稚鱼期;培育至57 d,稚鱼完成变态,成为幼鱼。第二背鳍棘和腹鳍棘的生长与收缩等石斑鱼类早期发育的共性生长特征及其体表特性体色变化特征为驼背鲈胚后发育过程中最明显的特征。     

Effect of Temperature on Growth,Energy Budget,and Physiological Performance of Green,White, and Purple Color Morphs of Sea Cucumber,Apostichopus japonicus

As an intertidal species, Apostichopus japonicus is subject to diel and seasonal temperature fluctuations. Color variation is a distinct characteristic of A. japonicus, and a new color morph, purple A. japonicus, was recently found on the coast of Rushan, Weihai City. This study was conducted to compare the performance of green, white, and purple color morphs of A. japonicus at different water temperatures to help improving aquaculture technology and management. In this study, green, white, and purple color morphs of juvenile A. japonicus (1.5 ± 0.1 g) were cultured at 10, 14, 18, 22, and 26 C for 60 d, according to the suitable temperature range for sea cucumber growth. Temperature was shown to have a significant effect on growth, energy budget, and physiology of sea cucumbers (P < 0.05). Specific growth rates, feed conversion efficiencies, and the proportion of energy allocated to growth of all three color morphs were optimal at 18 C. Activities of the enzymes related with oxidative stress, immune response, and digestion were determined. Superoxide dismutase (SOD) and trypsin activities generally reached a maximum in all three color morphs at 18 C. The purple color morph of A. japonicus was higher in growth rate, food conversion efficiency, and proportion of energy allocated to growth than green and white color morphs at 18 and 22 C, consistent with its higher trypsin and SOD activity, indicating the mutual effect of growth and physiology. At 18, 22, and 26 C, the green color morph had the highest level of lysozyme activity and purple color morph had the lowest, indicating possible infection by external pathogens of green color morph, which might be caused by high temperature. These results suggested that the optimum temperature for culture of the three color morphs was approximately 18 C, the purple had a better adaption to high temperature, and the green and white color morphs may be more susceptible to thermal stress than the purple color morph.     

Effects of Mosquitofish,Gambusia affinis,on Channel Catfish,Ictalurus puncatatus,Production Ponds

Mosquitofish, Gambusia sp., have been spread throughout the world to biologically control mosquitoes. However, the fish has gained a reputation as an invasive species and has been implicated in displacing native aquatic species. Gambusia affinis are native to the southeastern United States and commonly occur in commercial channel catfish, Ictalurus punctatus, production ponds. We investigated effects of mosquitofish presence on zooplankton populations, water quality, disease occurrence, and fish production in experimental ponds. There were no differences between ponds with or without mosquitofish in numbers of calanoid copepods, cyclopoid copepods, total copepods, Bosmina sp., Ceriodaphnia sp., Moina sp., Daphnia sp., or total cladocerans. There were also no differences in copepod and cladoceran sizes. Copepod nauplii were more numerous during the summer months in ponds with mosquitofish. There were no differences in water quality variables (soluble reactive phosphorus, nitrate, nitrite, ammonia, total nitrogen, total phosphorus, pH) or phytoplankton density between ponds stocked with and without mosquitofish. Catfish production and disease occurrence were also similar between ponds with and without mosquitofish. Although mosquitofish may cause problems when stocked outside their native range, there does not appear to be any adverse effects of mosquitofish presence in catfish production ponds.     

Age,growth, maturity and the overfishing of the iconic sciaenid,Argyrosomus japonicus,in south-eastern,Australia

Mulloway (Argyrosomus japonicus) occur in estuarine and coastal waters surrounding Australia, Africa, India, Pakistan, China, Korea and Japan, where they are important in fisheries. This study identified that mulloway in south-eastern Australia had similar growth rates, but matured at smaller lengths and younger ages, to those in South Africa and Western Australia. Growth of both sexes was similar to about 5 years, after which females grew faster and attained a greater maximum length than males. Female mulloway matured at 4–5 years of age with a L₅₀ of 68 cm, whereas males matured at 2–3 years of age with a L₅₀ of 51 cm. The commercial fishery in New South Wales was characterised by declining catches and a reduction in the proportion of mulloway of mature lengths in landings. During 2002–2005 commercial landings were dominated (83%) by fish within 15 cm of the current minimum legal total length of 45 cm and aged 2 and 3 years (>80%), even though mulloway can attain lengths of 200 cm and live >30 years. Estimates of the rates of instantaneous total mortality ranged between 0.34 and 0.45, whilst the rate of instantaneous natural mortality (M) was estimated to be approximately 0.12. Yield-per-recruit analyses indicated that mulloway in New South Wales are being growth overfished and substantial increases in yield could be achieved by increasing the length at first harvest. Values of the spawning potential ratio were below 0.2 under a range of mortality estimates, suggesting that mulloway are at risk of recruitment overfishing. These results suggest that the spawning stock of mulloway in south-eastern Australia has been depleted and that remedial management action is required to protect this iconic species.     

Effect of Lead on Survival,Osmoregulation, and Histological Changes of the Gills of the White Shrimp,Litopenaeus vannamei,Boone, 1931

The purpose of this study was to evaluate the acute toxicity of lead for different life stages of shrimp, Litopenaeus vannamei, and to determine the effect of its sublethal concentrations on osmoregulatory capacity (OC) as well as the possible histological alteration in the gills of juvenile shrimp. The 24‐, 48‐, and 96‐h LC₅₀ values for lead to L. vannamei increased progressively with increasing life stage, from nauplii < zoeae < mysis < postlarvae < juvenile. After 15‐d exposure to 3.25, 6.50, and 9.75 mg Pb/L, the OC values of exposed shrimp were reduced by 39, 73, and 157%, respectively compared to control animals. Compared to controls, the lead concentrations in gill tissues increased significantly by 127,500, 137,500, and 141,000% in shrimps exposed to 3.25, 6.50, and 9.75 mg Pb/L, respectively. After lead exposure, hemocytic congestion in efferent vessels and multiple hyperplasia were observed in gill filaments, resulting in narrowed hemolymphatic lacuna. The histopathological effects increased with increasing Pb concentration.     

Recruitment strategy of swimming crab, Portunus trituberculatus, in Hiuchi-Nada, Japan

The recruitment strategy of swimming crabs, Portunus trituberculatus, was investigated by field observations and numerical experiments in Hiuchi-Nada, Japan. Calculated dispersal patterns of zoeal and megalopal stages in a three-dimensional numerical model reproduce observed patterns accurately. The temporal change of vertical migration patterns between the 1st and 2nd zoeas and the 3rd and 4th zoeas plays an important role in the process of recruitment of P. trituberculatus from spawning ground to nursery ground.     

Effect of Salinity on Embryonic Development,Hatchability, and Growth of African Catfish,Clarias gariepinus,Eggs and Larvae

Abstract

Effects of salinity on embryonic development and growth of African catfish, Clarias gariepinus, eggs and larvae were studied. Eggs were incubated at 27-29°C in 2,4,6,8, and 10 ppt sodium chloride. Rate of embryonic development was delayed in all salt solutions by 15, 15,28 and 30 minutes, in 2,4,6, and 8 ppt sodium chloride, respectively, when compared with the control group (0% salt); total mortality occurred at 12 hours after gastrula stage in the 10 ppt concentration. Percentage hatching was 45.1,47.7, 59.5,49.2, and 26.6% while percentage deformity was 10.4, 16.1, 52.0, 28.6, and 71.6% in 0, 2, 4, 6, 8, and 10 ppt salt treatments, respectively. There were significant differences (P <0.05) in the hatching percentage and in deformity percentage between 4, 6, and 8 ppt. Rate of yolk absorption was significantly faster in the control and 2 ppt salt treatments, but slower in 4, 6, and 8 ppt. Rate of increase in length was slower with increasing salinity. The optimum salinity for African catfish eggs and was between 0-2 ppt and acceptable up to 6 ppt. The results suggest that increasing salinity delayed hatching and development of African catfish eggs and larvae, respectively, as well as increased the deformity of the larvae.     

Effect of Stocking Density on Growth,Yield, and Costs of Producing Rainbow Trout,Oncorhynchus mykiss,in Cages

Abstract

Rainbow trout, Oncorhynchus mykiss, were raised in culture cages (1 m³) to determine the effect of stocking density on growth, survival, and percentage of market-size fish. Large fingerling rainbow trout (20-25 cm, 232 g average weight) were stocked into six cages located in a 0.4-ha pond. Two stocking densities (100 or 200 fish/cage) were used, and fish were grown for 140 days (2000-April 2001). Average total harvest weight (35.0 kg) in the low-density cages was approximately one-half the average total harvest weight (61.2 kg) in the high-density cages. Average weight gain (11.7 kg to 15.1 kg) and feed conversion (1.2 to 1.5) were also smaller for the low-density cages. Average survival was 96.7% for the low-density cages and 94.2% for the high-density cages, with the percentage of market-size fish (< 29 cm) averaging 50.3% and 52.0%, respectively. Production costs for the actual experiment and the revenues from fish sold at the end of the study were collected. An enterprise budget based on the experimental results for the two densities was developed to determine if a culture operation of this size would produce a net return. Production costs and revenues from the experiment resulted in a large negative return (-$3,124) and high breakeven price ($13.53/kg).