盐度胁迫对三疣梭子蟹肌肉和血淋巴中游离氨基酸含量的影响

为探究不同盐度环境下三疣梭子蟹肌肉和血淋巴中游离氨基酸(free amino acids,FAAs)的含量及浓度的变化规律,明确FAAs的组成以及在盐度适应中发挥的作用,丰富FAAs在甲壳动物盐度适应领域的研究,为后续分子机理的研究提供依据,实验设定胁迫盐度分别为10、20、40、50,以正常海水(盐度33)为对照,用日立835-50型氨基酸自动分析仪测定三疣梭子蟹血淋巴与肌肉组织中游离氨基酸的组分,分析不同盐度环境下三疣梭子蟹肌肉和血淋巴中FAAs的含量及变化规律。结果显示,在正常海水中三疣梭子蟹血淋巴和肌肉中含量较高的FAAs主要为牛磺酸(Tau)、精氨酸(Arg)、甘氨酸(Gly)、脯氨酸(Pro)和丙氨酸(Ala)。盐度为10~50,梭子蟹肌肉和血淋巴总游离氨基酸(total free amino acid,TOFAA)的含量随盐度的增加而显著升高,非必需氨基酸(non-essentical free amino acid,NEAA)的含量随盐度的升高而上升,而必需氨基酸(essentical free amino acid,EAA)的含量变化不显著,因此,TOFAA在渗透压调节方面的作用主要取决于NEAA。发挥主要渗透压调节作用的FAAs为脯氨酸(Pro)、丙氨酸(Ala)、甘氨酸(Gly)、天冬氨酸(Asp)、谷氨酸(Glu)。Ala、Gly、Asp、Glu属于鲜味氨基酸(taste amino acid,TAA),研究表明,NEAA中的TAA在渗透压调节方面作用显著,Pro含量的升高对TOFAA含量的增加作用显著,盐度为40~50尤甚,表明Pro在梭子蟹高渗调节中发挥重要作用。     

盐度对凡纳滨对虾肌肉中游离氨基酸含量的影响

通过逐渐升高盐度的方法,分别测定盐度为0、10、20、30和40时凡纳滨对虾肌肉中游离氨基酸(FAA)的含量,实验周期40 h。结果表明:在盐度0~40时,总游离氨基酸(TOFAA)、必需氨基酸(EAA)、非必需氨基酸(NEAA)和鲜味氨基酸(TAA)的含量都随盐度的增加而明显升高(P0.05);特别是当盐度从20增加到30时,肌肉中TOFAA、EAA、NEAA和TAA含量的增高幅度最明显。在凡纳滨对虾肌肉FAA中,含量最高的是甘氨酸(Gly),其次是脯氨酸(Pro)、精氨酸(Arg)和丙氨酸(Ala)。在盐度为0~40范围内,肌肉中主要的渗透压调节因子是甘氨酸(Gly)、脯氨酸(Pro)、精氨酸(Arg)、丙氨酸(Ala)和牛磺酸(Tau);而天冬氨酸(Asp)、丝氨酸(Ser)、缬氨酸(Val)、甲硫氨酸(Met)、异亮氨酸(Ile)、亮氨酸(Leu)和酪氨酸(Tyr)的含量在各盐度组未呈现显著变化(P0.05)。在淡水养殖凡纳滨对虾出售前的40 h,通过提高水体盐度来提高凡纳滨对虾肉质的鲜味是完全可行的。     

盐度胁迫对魁蚶稚贝血淋巴渗透压及鳃Na~+/K~+-ATP酶活力的影响

文章研究了盐度胁迫下魁蚶(Anadara broughtonii)稚贝(壳长25~35 mm)血淋巴渗透压和鳃Na+/K+-ATP酶活力的变化。结果显示,突变胁迫下,盐度20、25、35、40组的稚贝血淋巴渗透压均在48 h内显著降低或波动升高后趋于稳定,盐度15组则需96 h完成波动调整。以日变幅5渐变至高盐40过程中,稚贝血淋巴渗透压在48 h内趋于稳定;低盐15组仅需72 h完成渗透压调节,调整时间显著小于突变组。盐度突降胁迫下,各处理组稚贝鳃Na+/K+-ATP酶活力12 h后显著升高,24 h分别达到最大值,随后快速回落并稳定在高于对照组水平;盐度骤升胁迫下,鳃ATP酶活力波动降低,在12~24 h达到最小值后稳定在低于对照组水平。低盐(15)和高盐(40)渐变组的鳃ATP酶活力变幅均小于突变组。盐度胁迫下鳃Na+/K+-ATP酶活力的响应方式不同,即低盐胁迫时活力增强,高盐胁迫时活力降低。采用盐度渐变的驯化处理更有利于魁蚶稚贝应对盐度胁迫。     

盐度胁迫对三疣梭子蟹(Portunus trituberculatus)鳃中游离氨基酸含量的影响

本研究分析了不同盐度环境下三疣梭子蟹(Portunus trituberculatus)鳃组织中游离氨基酸(FAAs)的含量及浓度变化规律,明确 FAAs 的组成及其在盐度适应中发挥的功能。结果显示,在正常海水中,三疣梭子蟹鳃组织中牛磺酸(Tau)的浓度最高(2.54 mg/g),其次分别为丙氨酸(Ala,0.65 mg/g)、谷氨酸(Glu,0.64 mg/g)、精氨酸(Arg,0.58 mg/g)、甘氨酸(Gly,0.48 mg/g)和脯氨酸(Pro,0.25 mg/g);在盐度10–50范围内,梭子蟹鳃中总游离氨基酸(TOFAA)的含量随盐度的增加而显著升高(P<0.05),盐度50时,TOFAA 的含量为盐度10时的1.48倍。进一步分析发现,非必需氨基酸(NEAA)(Gly、Glu、Ala 和 Pro)的浓度随盐度的升高而上升,而必需氨基酸(EAA)的浓度变化不显著(P>0.05)。研究表明,FAAs 在三疣梭子蟹盐度适应中具有重要功能,其中发挥渗透调节功能的主要为 NEAA。     

盐度胁迫对三疣梭子蟹(Portunus trituberculatus)鳃中游离氨基酸含量的影响

本研究分析了不同盐度环境下三疣梭子蟹(Portunus trituberculatus)鳃组织中游离氨基酸(FAAs)的含量及浓度变化规律,明确FAAs的组成及其在盐度适应中发挥的功能。结果显示,在正常海水中,三疣梭子蟹鳃组织中牛磺酸(Tau)的浓度最高(2.54 mg/g),其次分别为丙氨酸(Ala,0.65 mg/g)、谷氨酸(Glu,0.64 mg/g)、精氨酸(Arg,0.58 mg/g)、甘氨酸(Gly,0.48 mg/g)和脯氨酸(Pro,0.25 mg/g);在盐度10–50范围内,梭子蟹鳃中总游离氨基酸(TOFAA)的含量随盐度的增加而显著升高(P0.05),盐度50时,TOFAA的含量为盐度10时的1.48倍。进一步分析发现,非必需氨基酸(NEAA)(Gly、Glu、Ala和Pro)的浓度随盐度的升高而上升,而必需氨基酸(EAA)的浓度变化不显著(P0.05)。研究表明,FAAs在三疣梭子蟹盐度适应中具有重要功能,其中发挥渗透调节功能的主要为NEAA。     

大菱鲆水通道蛋白(AQP1、AQP3)以及离子通道蛋白(CFTR、NHE1)对低盐胁迫的响应

在鱼类适应环境盐度变化的过程中,鳃、肾、肠是主要的渗透调节器官,而水通道蛋白(Aquaporins, AQPs)、囊性纤维化跨膜传导调节因子(CFTR)、钠氢交换体(NHE)又是这些器官中重要的渗透调节基因。为研究AQP1、AQP3、CFTR、NHE1在大菱鲆(Scophthalmus maximus)低盐胁迫过程中的渗透调节功能,本研究采用荧光定量PCR技术,对4种基因在盐度5和盐度10下大菱鲆鳃、肾、肠中表达量随时间的变化进行检测。结果显示,AQP1表达量在鳃中极少(P<0.05),在肾和肠中较高,低盐胁迫下,盐度5组和盐度10组在鳃中的表达量无显著变化,在肾和肠中均显著上升(P<0.05)。AQP3表达量在肾中极少(P<0.05),在鳃中较高,在肠中较少,低盐胁迫下,盐度5组和盐度10组在肾中的表达量无显著变化,在鳃和肠中均显著上升(P<0.05)。CFTR表达量在肾中极少,在鳃中较高,在肠中较少,低盐胁迫下,盐度5组和盐度10组在肾中的表达量无显著变化,在鳃和肠中均显著下降(P<0.05)。NHE1在鳃和肠中表达量较少,在肾中较高,低盐胁迫下,盐度5组和盐度10组在鳃中的表达量无显著变化,在肾和肠中均显著上升(P<0.05)。这些结果表明,4种基因表达水平因组织、盐度和时间的不同而不同,反映了这4种基因的功能特异性;在低盐胁迫下,4种基因积极响应,表达量均发生不同程度的变化,表明AQP1、AQP3、CFTR和NHE1在大菱鲆低盐环境适应中可能具有潜在的重要作用。另外,本研究结果可为大菱鲆半咸水养殖和淡化养殖提供理论依据,同时为培育适应低盐环境大菱鲆良种提供理论和技术支撑。     

盐度对瘤背石磺血淋巴生理生化指标及免疫应激指标的影响

为探讨盐度对瘤背石磺(Onchidium struma)血淋巴生理生化指标及免疫指标的影响,用不同盐度水平(5、15、25、35和45)的人工海水饲养瘤背石磺幼贝[湿重(2.96±1.02)g]60 d后测定瘤背石磺血淋巴生理生化指标及免疫指标。结果显示:盐度对瘤背石磺血淋巴生化指标和免疫应激指标均有显著影响。低盐度时血糖浓度显著高于高盐度;白蛋白、球蛋白和总蛋白含量均呈现先下降后上升再下降趋势,且均在盐度25时最低;而随着盐度的升高,瘤背石磺血淋巴中甘油三酯含量呈下降趋势,但无显著影响。碱性磷酸酶活性随着盐度的升高呈现下降趋势,而谷丙转氨酶随着盐度的升高呈现抛物线变化,且在盐度15时最高。免疫指标与血液生化指标相一致,均在盐度胁迫时,诱导瘤背石磺机体发生一系列反应,对机体产生一定的损伤。试验结果表明,在低盐度时,瘤背石磺用于渗透压调节的能量多于高盐度,且过高和过低盐度均对瘤背石磺的肝胰腺产生损伤,造成血淋巴中谷丙转氨酶含量增多。     

盐碱胁迫对尼罗罗非鱼鳃Na+/HCO3-共转运子、碳酸酐酶基因表达的影响

为了探讨盐碱胁迫条件下鱼类渗透生理调节机制,以尼罗罗非鱼(Oreochromis niloticus)为实验材料, PCR扩增得到了Na+/3HCO-共转运子(NBCe1)基因cDNA部分序列,比较了单盐(盐度10、盐度15)、单碱(1.5 g/L、3 g/L NaHCO3)、盐碱混合(盐度10,碱度1.5 g/L;盐度15,碱度3 g/L)胁迫后不同时间(0 h、6 h、12 h、24 h、48 h、72 h、96 h)血清渗透压、离子浓度(Na+、K+、Cl–、Ca2+)以及鳃碳酸酐酶(CA)活性、CA与NBCe1基因mRNA表达变化。结果显示,不同胁迫条件下,血清渗透压、离子浓度、鳃组织 CA 酶活、CA 与 NBCe1基因 mRNA 表达变化均与胁迫强度呈正相关。随时间推移,血清渗透压、离子浓度呈现先上升后下降的变化趋势,单盐、盐碱混合组血清渗透压值较单碱组高。单盐、单碱、盐碱混合组中, NBCe1基因mRNA在鳃中均呈略微上调,但不显著(P>0.05)。单碱组和盐碱混合组鳃CA活性较单盐组高,低盐碱胁迫(盐度10,碱度1.5 g/L)下CA活性较晚达最高值;不同胁迫条件下, CA基因mRNA表达均表现上调,单碱、盐碱混合组更为显著(P<0.05),推测CA较NBCe1对体内3HCO-转运作用更为显著。研究结果为尼罗罗非鱼盐碱适应生理调节提供了基础资料。     

不同盐度对凡纳滨对虾血淋巴及肌肉游离氨基酸组成的影响

以平均体重为10.50±1.75g的凡纳滨对虾为研究对象,分别在盐度为0、15和30的水体中用同一种饲料喂养20d,探讨不同盐度对凡纳滨对虾肌肉及血淋巴游离氨基酸组成的影响。结果表明,盐度在0、15和30变化时,凡纳滨对虾血淋巴中总游离氨基酸总量随盐度升高而显著增加（P〈0.05）;甘氨酸、谷氨酸、精氨酸和丙氨酸是凡纳滨对虾血淋巴中主要的游离氨基酸成分,其含量随盐度的增加而急剧增加。盐度为0、15和30时,凡纳滨对虾肌肉中游离氨基酸总量随着盐度的增加有增加趋势,但无显著性差异（P〉0.05）。甘氨酸、亮氨酸、苯丙氨酸及精氨酸的含量随盐度由0、15、30的增加而显著增加（P〈0.05）;其他氨基酸在盐度0、15和30增加时,虽无显著性增加（P〉0.05）,但大部分氨基酸有增加趋势。当盐度在0、15和30变化时,游离甘氨酸、谷氨酸、精氨酸和丙氨酸是凡纳滨对虾体内渗透压调节的主要氨基酸。     

盐度对中华绒螯蟹交配及产卵前后血淋巴中5种激素的影响研究

为探究盐度在中华绒螯蟹(Eriocheir sinensis)交配和产卵前后对血淋巴中5种激素的影响,本研究分别设置了0、2、4、6的交配盐度和3、6、9、12、15、18、21的产卵盐度,分析了不同交配和产卵盐度条件下,中华绒螯蟹血淋巴中双羟基孕酮(DHP)、促性腺激素(GTH)、前列腺素(PG)、雌二醇(E2)和睾酮的含量变化。结果显示,在淡水中,雌蟹无交配行为发生,当盐度<6时,雌蟹只交配不产卵。雌蟹在盐度为2～6中交配后,血淋巴中GTH、PG、E₂和睾酮与交配前相比均无明显变化,且交配后各盐度组相比无显著差异(P>0.05)。随着盐度的升高,雌蟹产卵前,血淋巴中DHP、PG、E₂和睾酮的含量均呈先下降再上升的趋势;产卵后血淋巴中DHP、PG、E₂则呈先上升后下降的趋势,其中,当盐度为18时,雌蟹产卵后,血淋巴中DHP、GTH、PG、E₂和睾酮含量均降到最低,且与产卵前相比均有显著差异(P<0.05)。当盐度为6时,雌蟹产卵前血淋巴中DHP、PG、E₂和...     

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.     

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).     

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.     

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.     

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.     

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.     

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).