对虾源副溶血弧菌拮抗菌的筛选与评价

随着对虾养殖产业集约化程度不断提高,对虾病害的发生越来越多,成为制约产业发展的主要因素。自江苏南部沿海滩涂沉积物中分离得到252株细菌,以14株凡纳滨对虾急性肝胰腺坏死综合征致病性副溶血弧菌为指示菌,经过初筛和复筛,得到1株拮抗效果较好的菌株H0011;经形态、生理生化特性和16S rDNA基因序列鉴定,确定菌株H0011为普罗威登斯菌。利用普罗威登斯菌H0011对凡纳滨对虾进行高密度胁迫试验测试其安全性,试验期间浸浴组和投喂组对虾状态良好,无发病和死亡现象。对普罗威登斯菌H0011的生长条件优化后,最优生长温度为30℃,盐度为10,pH为8。普罗威登斯菌H0011 4 h进入对数生长期,20 h达到生长高峰。本研究获得了对凡纳滨对虾急性肝胰腺坏死综合征具有防控作用的高效拮抗作用菌,将为对虾急性肝胰腺坏死综合征的防控提供新的思路。     

凡纳滨对虾肠道铁载体高产菌株筛选与饲料添加应用效果的研究

本研究筛选了凡纳滨对虾(Litopenaeus vannamei)肠道铁载体高产菌株,并探究了饲料中添加铁载体高产菌株对凡纳滨对虾的生理功效。结果显示,从凡纳滨对虾肠道中筛选出一株铁载体产量高达74.87%的菌株SDVGH3,经鉴定属于泛菌属(Pantoea sp.),产生的铁载体属于异羟肟酸型,该菌株无溶血性,对大部分抗生素敏感;优化了该菌株铁载体产量的培养条件：最适温度为28℃,pH为7.5,盐度为0,装液量为10 mL,Fe3+浓度为0.01 mmol/L;采用滤纸片扩散法检测了菌株抑制病原菌的特性,显示能抑制5种凡纳滨对虾致病菌。通过在饲料中添加SDVGH3菌液,凡纳滨对虾增重率和饲料利用率明显升高,血细胞数量、吞噬率和血浆酚氧化酶、抗菌活性均有不同程度的升高,副溶血弧菌(Vibrio parahaemolyticus)攻毒后,实验组的死亡率显著低于对照组,1010 CFU/g实验组的死亡率最低,为61.4%;添加107 CFU/g SDVGH3菌液处理组,凡纳滨对虾肠道菌群多样性显著提高,弧菌属(Vibrio sp.)在肠道菌群中所占比例明显下降。研究表明,铁载体高产菌株SDVGH3能明显促进凡纳滨对虾生长、免疫防御能力,增强肠道菌群健康,具有应用于水产养殖中的潜力。     

盐度对凡纳滨对虾血细胞吞噬与免疫相关因子基因表达的影响

在水温27～29℃下,将平均体长7.01 cm的凡纳滨对虾Litopenaeus vannamei饲养在730 mm×530 mm×450 mm的水族箱中,每箱30只,盐度6、18和30,每个盐度组3个平行,饲养6周,探讨盐度对凡纳滨对虾血细胞吞噬与免疫相关因子基因表达的影响。结果表明:盐度30和18组凡纳滨对虾血细胞吞噬活性显著高于盐度6组对虾(P0.05),盐度18组血细胞吞噬活性最高。30和18盐度组凡纳滨对虾肝胰腺中Toll样受体(TLR)、免疫缺陷基因(immune deficiency,IMD)、酚氧化酶(PO)、过氧化氢酶(CAT)及溶菌酶(LZM)基因表达水平显著高于盐度6组(P0.05);18盐度组凡纳滨对虾血细胞中TLR、IMD、PO、SOD及LZM基因表达显著高于6盐度组(P0.05);盐度30组对虾的TLR基因表达水平显著高于盐度18组(P0.05),而盐度30组对虾的PO和CAT基因表达水平显著低于盐度18组(P0.05);其他免疫因子基因的表达水平没有显著性差异。综上,环境中盐度的变化可能通过影响凡纳滨对虾各组织的抗氧化能力、溶菌活性、识别能力和血细胞吞噬活性等,调控凡纳滨对虾细胞和体液免疫。     

凡纳滨对虾幼虾低盐度粗养水体养殖容量的研究

试验设计6个凡纳滨对虾幼虾养殖密度:10、20、30、40、50、60 ind/m2,通过比较60 d养殖周期内的水环境因子、幼虾生长状况与消化酶活性,分析研究凡纳滨对虾幼虾低盐度粗养水体的养殖容量。结果表明:各试验组水质均符合凡纳滨对虾幼虾生长要求,单位水体载虾量主要影响pH、非离子氨氮(NH3-Nm)、溶解氧(DO)等水化指标;不同试验组水体pH、NH3-Nm含量、DO含量、总氮(TN)含量差异极显著(P0.01),浊度、总磷(TP)含量差异显著(P0.05);不同试验组对虾中肠腺蛋白酶活性差异显著(P0.05),表现出单位水体载虾量越高,对虾体内蛋白消化酶活性和氮利用率越低的规律,DO是低盐度粗养水体养殖容量的主要限制因子。综合各项评价指标,得到本试验条件下,凡纳滨对虾幼虾低盐度粗养水体的最佳养殖容量为46.0 g/m3或32.2 g/m2(322 kg/hm2)。     

盐度和钠离子/钾离子对凡纳滨对虾幼虾存活与组织结构的影响

通过实验生态学方法,对体质量为(1.35±0.37) g的凡纳滨对虾(Litopenaeus vannamei)幼虾开展了盐度(2、4、8、12、16)和钠离子/钾离子(Na~+/K~+)(27、50、75、100、125、150)双因素胁迫实验,分析其对凡纳滨对虾的72 h成活率及肝胰腺和肌肉组织结构的影响。结果显示,在Na~+/K~+大于75的条件下,凡纳滨对虾的成活率随盐度的增加而降低;在盐度大于8的条件下,凡纳滨对虾的成活率随Na~+/K~+的降低而升高。在Na~+/K~+为27～75条件下,凡纳滨对虾的成活率均大于66.67%。Na~+/K~+为100条件下,凡纳滨对虾在盐度12和16下的半致死时间(LT50)分别为69.78和60.15 h。Na~+/K~+为125条件下,盐度8、12和16下的LT50分别为76.23、62.61和49.10 h。Na~+/K~+为150条件下,盐度4、8、12和16下的LT50分别为87.24、68.65、59.4和39.95 h。双因素方差分析表明,Na~+/K~+、盐度与凡纳滨对虾幼虾第72小时的成活率存在显著交互作用。组织切片显示,当盐度大于8时,高Na~+/K~+对肌肉和肝胰腺组织结构产生明显影响,主要表现为细胞空泡化或自溶,组织细胞间隙变大、解体,且组织结构损伤程度随盐度的上升而加重。     

2株副溶血弧菌不同盐度下致病性和毒力基因差异分析

副溶血弧菌(Vibrio parahaemolyticus)是常见的食源性致病菌和海水养殖动物致病菌,目前已知的毒力基因有tlh、tdh、trh、T3SS、pirA、pirB、toxR/S、orf8等。盐度是影响细菌基因表达的关键生态因子之一,为进一步探求副溶血弧菌的致病机理,对2株分别分离自海水和淡水养殖发病凡纳滨对虾(Litopenaeus vannamei)中的副溶血弧菌在不同盐度下的生长速率、致病性进行检测,并用q-PCR方法对菌株毒力基因携带和表达情况进行定量研究。实验结果表明:海水菌株383生长速率快于淡水菌株V9,但菌株383在生长稳定期的细菌浓度明显低于菌株V9;菌株383对凡纳滨对虾的致病性明显高于菌株V9,前者的48 h半致死浓度(LD_(50))低于后者2个数量级;2株副溶血弧菌皆携带毒力基因tlh、T3SS1和pirA/B,但未检测到tdh、trh、T3SS2、toxR/S和orf8。部分毒力基因表达量检测结果显示,菌株383和菌株V9均为vcrD1表达量最高,其次是pirA,vopD1表达量最低;4个毒力基因不仅在2菌株间的表达量差别较大,而且盐度对同一菌株不同毒力基因表达的影响也是不同的。2株副溶血弧菌的毒力与pirA和vcrD1的表达量呈正相关性。研究结果为探究环境因素与副溶血弧菌致病力的关系提供了科学依据,同时也提示,淡水养殖凡纳滨对虾要防范副溶血弧菌输入的风险。     

酵母水解物对低盐胁迫凡纳滨对虾非特异性免疫及抗氧化能力的影响

本实验旨在研究饲料中添加酵母水解物对凡纳滨对虾在低盐度胁迫条件下非特异性免疫和抗氧化能力的影响。选取凡纳滨对虾[初始体质量（15.82±0.08）g],平均分为2组,对照组投喂基础饲料（Y0）,实验组投喂添加了3%酵母水解物的实验饲料（Y3）,在室内养殖15d后分别放入盐度为4‰（S4）和28‰（S28）的水体中进行盐度胁迫实验,每组6个重复,每个重复30尾虾（根据饲料和盐度不同组合,分组命名为Y0S4、Y0S28、Y0S3、Y0S28）。结果表明：饲料中添加3%酵母水解物对凡纳滨对虾血清酚氧化酶（PO）、总一氧化氮合成酶（TNOS）活性没有显著影响,但低盐度胁迫1h时,Y3S4组PO、TNOS活性显著高于Y0S4组;盐度因素对PO、TNOS活性产生显著影响,低盐度胁迫1h时,S28组PO、TNOS活性显著高于S4;饲料中添加3%酵母水解物显著提高了凡纳滨对虾肝胰腺超氧化物歧化酶（SOD）活性;盐度因素对酸性磷酸酶（ACP）活性产生了显著影响,S28组ACP活性显著高于S4。由此可见,在饲料中添加酵母水解物能够提高凡纳滨对虾肝胰腺SOD活性,提高对虾的抗氧化能力;在遭遇低盐度胁迫时,对虾能迅速恢复PO、TNOS活性至正常水平,从而提高凡纳滨对虾的抵抗不良环境的能力。     

周期性盐度波动对凡纳滨对虾游离氨基酸含量及渗透调节相关基因表达的影响

在实验室条件下,以盐度30为对照组(S0),4 d为1个盐度波动周期,研究了幅度为4(S4)和10(S10)的周期性盐度波动对凡纳滨对虾(Litopenaeus vannamei)稚虾离子通道和水通道相关基因表达、游离氨基酸(FAA)含量及其FAA代谢相关基因表达的影响。结果发现:(1)在盐度波动条件下,凡纳滨对虾离子通道相关基因Na~+/K~+-ATPaseα(NKAα)、Na~+/K~+-ATPaseβ(NKAβ)、碳酸酐酶(CA)、V型H~+-ATPase 1(VHA 1)表达量随盐度波动幅度的增加而极显著升高(P0.01);S4组对虾Na~+/H~+交换因子(NHE)和F型H~+-ATPase 1(FHA 1)表达量显著高于S0和S10组(P0.05);而Cl-通道蛋白(CLC)表达量在各组间差异不显著(P0.05);(2)周期性盐度波动极显著影响凡纳滨对虾水通道蛋白(AQP 4)的基因表达(P0.01),其表达量随盐度波动幅度的升高而下降;(3)周期性盐度波动对凡纳滨对虾肌肉中FAA总量无显著影响(P0.05);鳃中FAA总量随盐度波动幅度的增加而显著升高(P0.05),各组甘氨酸、精氨酸、脯氨酸等含量存在显著差异(P0.05)。(4)与S0组相比,S10组对虾的丙氨酸转氨酶(ALT)表达量极显著升高,S4和S10组对虾的氨基转移酶(AMT)、脯氨酸脱氢酶(PDH)基因表达量极显著降低(P0.01)。实验结果初步表明,周期性盐度波动条件下,凡纳滨对虾渗透调控在转录水平上产生积极响应,且随着盐度波动幅度的增大,对虾的渗透适应性调控水平升高。在盐度波动幅度达到10时,凡纳滨对虾仍能维持体内的渗透平衡,说明其具有较强的耐受盐度波动的能力。     

凡纳滨对虾肠道内产消化酶益生菌的分离与筛选

为获得具有消化酶活性且安全的益生菌,从凡纳滨对虾肠道中初步分离得到576株细菌,对菌株进行产蛋白酶、淀粉酶和脂肪酶能力的定性及定量测试,筛选出产酶种类多且产酶能力强的菌株11株。对筛选出的11株菌进行了幼虾浸浴实验、药敏性实验和溶血性实验,以评价其生物安全性。将11株菌的菌悬液添加到凡纳滨对虾幼虾的养殖水体中进行浸浴实验,浸浴结束后用鳗弧菌进行刺激,测定不同浸浴组幼虾相关免疫基因的相对表达量,以确定其对幼虾的保护效果。综合消化酶活性、菌株对幼虾的保护效果及生物安全性,筛选得到4株效果较好的菌株。菌株的16S r DNA分子鉴定结果表明,细菌1号、2号和4号分别与芽孢杆菌(Bacillus sp.PCSAS2-38,GQ284495.1)、蜡样芽孢杆菌(B.cereus strain N419,JN400121.1)及苏云金芽孢杆菌(B.thuringiensis strain EA26.1,KC758847.1)的相似性均为100%,9号菌株与荚膜红细菌(Rhodobacter capsulatus strain PSB-03,FJ866782.1)相似性达到99%,为后续益生菌制剂的开发奠定了前期基础。     

2株消化道优势菌对凡纳滨对虾免疫酶活性和抗白斑综合征病毒感染力的影响

以凡纳滨对虾为研究对象,在基础饲料中分别添加从健康对虾消化道中分离纯化的优势菌菌株——美人鱼发光杆菌PC463和坚强芽孢杆菌PC465(菌含量≥1011CFU/g)的活菌和破碎菌各1 g/kg,观察其对凡纳滨对虾血淋巴免疫酶活性和抗WSSV感染保护率的影响。经过20 d养殖实验后发现,与对照组相比,饲料中添加坚强芽孢杆菌活菌的免疫组和添加美人鱼发光杆菌灭活菌的免疫实验,其凡纳滨对虾血淋巴中酸性磷酸酶(ACP)、碱性磷酸酶(AKP)、超氧化物歧化酶(SOD)和过氧化氢酶(CAT)活性在不同程度上有所提高,并显著高于对照组(P<0.05)。WSSV感染后饲料中添加坚强芽孢杆菌活菌的免疫组存活率(53%±12%)和添加美人鱼发光杆菌灭活菌的免疫组存活率(49%±15%)显著高于对照组(P<0.05)。结果表明:饲料中添加坚强芽孢杆菌活菌和美人鱼发光杆菌灭活菌可以在一定程度上提高凡纳滨对虾免疫酶活性和抗WSSV感染能力,上述有防病作用的益生菌株以饲料添加剂的方式应用于对虾养殖生产,可望成为对虾白斑病生物防治的有效途径之一。     

一株芽孢杆菌的分离鉴定及在生物絮团对虾养殖中的应用

从对虾养殖池中分离到1株细菌(编号2013042402,简称菌株02),分别用16S rDNA序列比对法和细菌全细胞脂肪酸气相色谱法对该菌进行鉴定.结果显示,菌株02为芽孢杆菌(Bacillus sp.).为探讨该芽孢杆菌在生物絮团对虾养殖中的使用效果,实验分别设置加菌加糖组(菌株02的量为2.0× 104 CFU/ml,蔗糖量为饵料的70％)、加菌组、加糖组(生物絮团组)及空白对照组,研究了菌株02对养殖水质(温度、盐度、溶氧、pH、氨氮及亚硝酸氮)、对虾存活率及水体中主要菌群组成等指标的影响.结果显示,加菌加糖组能显著降低养殖水体中的氨氮和亚硝酸氮浓度,提高对虾存活率.生物絮团对虾养殖系统中添加菌株02,能够改善菌群结构,抑制弧菌生长.研究结果可为生物絮团对虾养殖中定向培养有益微生物提供技术支持.     

A high amylase‐producing bacterial strain exhibiting the phosphorus‐dissolving ability,isolated from freshwater aquaculture pond

Amylase‐producing bacteria could improve water quality contaminated by waste from feed residue and fish metabolism, thereby increasing the efficiency of aquaculture systems. The objective of this research was to screen and optimize fermentation conditions of a high amylase‐producing strain. Four amylase‐producing bacterial strains (named S458‐1, G05, H38 and B09) were isolated from a grass carp pond, and the strain S458‐1 showed the highest amylase‐producing ability, with 19.58 ± 0.38 mm hydrolysis circle diameter. The strain S458‐1 was identified as Bacillus cereus based on morphological identification, biochemical identification and 16S rDNA sequence analysis. The optimal culture medium formula included (in g/L) Ca²⁺ 0.8, Mg²⁺ 0.2, Mn²⁺ 0.4, Fe²⁺ 0.6, Al³⁺ 0.2, 1% soluble starch and 1% peptone. The optimal fermentation conditions were determined as initial pH 9, culture temperature 37°C, fermentation time of 60 hr and 2% inoculum. Under the optimal formula and condition, its enzyme activity increased from 32 U/ml to 173.01 U/ml, a 5.41‐fold increase. Surprisingly, our research found that the strain S458‐1 also had phosphorus degradation capabilities. Its phosphorus‐dissolving ability was both time‐ and concentration‐dependent. Thus, this study will make a contribution to the bacterial amylase based on the fermentation process and provide a theoretical basis for further research of aquatic probiotics.     

Lethal Low Dissolved Oxygen Concentrations for Postlarvae and Early Juvenile Penaeus setiferus at Different Salinities and pH

Abstract This study was undertaken to determine the effect of salinity and pH on tolerance to low dissolved oxygen concentration in postlarval (PL 12; 18 mg wet weight) and early juvenile (720 mg wet weight) Peneaus setiferus . Lethal levels of dissolved oxygen were determined in animals at four combinations of salinity and pH (36 and 15 ppt salinity and pH 6 and 8). For postlarvae, the 48-h LC50 for dissolved oxygen was 1.27 mgO₂/L at 15 ppt and pH8, and was significantly lower than that obtained in the other combinations of salinity and pH (P < 0.05). For juveniles, the 72-h LC50 was 1.16 mg1L at 15 ppt and pH 8, and was significantly lower than that obtained in the other combinations of salinity and pH (P < 0.05). A significant interaction between salinity and pH was observed. These results suggest that the intensive culture of P. setiferus may be conducted at moderate salinity, where shrimp appear to be more tolerant of low concentrations of oxygen than at higher salinities.     

Studies of the Thermal and Haline Influences on Growth and Survival of Litopenaeus vannamei and Litopenaeus setiferus

A series of experiments were conducted to examine the effects of salinity (1–48 g/L) on the biological performance, as evaluated by growth and survival, of the Pacific white shrimp, Litopenaeus vannamei, and the Atlantic white shrimp, Litopenaeus setiferus, reared at temperatures of 20, 24 or 28 C. Poor growth and survival of L. vannamei was observed after 21–28 d of culture at low salinity (2 and 4 g/L) at 20 C. Raising salinity to 8 and up to 32 g/L significantly increased survival at this temperature, indicating that avoiding low temperatures is critical for survival of this species when reared at low salinity. A major improvement in the growth rate of L. vannamei was observed at 24 C, but it still was sub‐optimal compared to growth observed at 28 C. Irrespective of salinity, high survival rates were observed at both 24 and 28 C, but variable growth rates were recorded. Contrary to L. vannamei, the Atlantic white shrimp, L. setiferus, which was reared for 28 d at 24 C only, had better growth performance at 8 g/L compared to 2, 16 and 32 g/L. Under equal experimental conditions, L. setiferus had considerably lower weight gain and survival than L. vannamei.     

4株凡纳滨对虾肠道益生菌分离、鉴定及应用研究

为将凡纳滨对虾肠道分离的益生菌用于对虾的养殖,利用乳酸菌培养基分离对虾肠道中的益生菌并对菌株进行初步分类鉴定,利用体外抑菌方法筛选有抗菌活性的菌株,用于考察对虾实验室养殖过程中抗有关致病菌的效果。试验结果显示,自虾肠道分离得到W7、W25、W27、W31菌株,分别属于啤酒酵母、短小芽孢杆菌、枯草芽孢杆菌沙漠亚种和暹罗芽孢杆菌,它们对致病菌副溶血弧菌、金黄色葡萄球菌和沙门氏菌有一定的抗菌活性,其中暹罗芽孢杆菌W31抗菌效果最好。将啤酒酵母W7和暹罗芽孢杆菌W31菌体与饲料混合用于对虾的养殖,能够明显增强凡纳滨对虾抵抗弧菌侵染的能力,提高存活率。     

生物絮团中异养亚硝化菌的分离鉴定及其特性

采用富集培养、分离纯化等微生物学手段,从对虾养殖池的生物絮团中筛选出两株对氨氮具有高转化率的菌株.16S rRNA测序及系统发育分析结果表明,两株菌均属于盐单胞菌属,菌株2011072708与食物盐单胞菌Halomonas alimentaria有99％的同源性,而菌株2011072709与胜利盐单胞菌H.shengliensis有100％的同源性.比较研究了两株菌在不同温度、盐度、pH、碳氮比条件下对氨氮的转化率,菌株2011072708在温度37℃、盐度30～40、pH 8、碳氮比28的条件下对氨氮的转化率最高;菌株2011072709在温度27～42℃、盐度40～50、pH 6、碳氮比21的条件下对氨氮的转化率最高.研究结果表明,胜利盐单胞菌（2011072709）对温度、盐度、pH、碳氮比等各方面的适应性优于食物盐单胞菌（2011072708）,更适合在生物絮团技术中得到应用.     

Physico‐chemical characteristics of the improved extensive shrimp farming system in the Mekong Delta of Vietnam

Consecutive failure of the improved extensive shrimp farming system has deterred the economy of some coastal areas in Vietnam. To investigate pond physico‐chemical characteristics, a monitoring scheme was performed in the Cai Nuoc district of Southern Vietnam. Results show that the system was not optimal for shrimps. While ponds were not contaminated by organic loadings or major nutrients (N, P) and salinity and pH were most optimal for shrimp, more than 37% of dissolved oxygen (DO) measurements were lower than recommended. In the early morning hours, DO measurements were even much lower (0.84–2.20 mg L^?1). Sulphate (SO₄^2?) concentrations were most within the acceptable range. Total suspended solids (TSS) were above the acceptable limit (<50 mg L^?1). Iron, alkalinity and hydrogen sulphide were also higher than recommended. Pond sediment was anaerobic (redox potential ?422 to ?105 mV) and contained high amounts of organic matter (9.84–21.96%). Lethal DO levels, high TSS and anoxic sediment are the drawbacks in this system. Suggested measures to improve pond conditions are (1) allowing sedimentation before filling culture ponds, (2) covering dikes, (3) including no‐culture breaks between shrimp crops, (4) drying pond bottom, (5) removing sediment and (6) controlling pond's vegetation.     

鳗草根际固氮菌的分离鉴定及培养条件的筛选

为了解鳗草(Zostera marina)根际微生物的共生固氮功能,并分离得到对海草有潜在促生效果的功能微生物,以山东荣城天鹅湖鳗草为研究对象,采用选择性固氮培养基从其根际分离得到了两株具较高固氮酶活性的菌株(3A和4G),从形态学、生理生化特性、16S rDNA和固氮基因nifH等方面对菌株进行筛选和鉴定,探讨菌株的最佳培养条件并获得了菌株典型生长曲线。结果表明,菌株3A为海旋菌(Thalassospira),革兰氏阳性菌,菌落圆形桔黄色,可利用的碳源:D-甘露糖,D-松三糖,L-鼠李糖等,最佳培养条件:盐度2.585%,pH 8.18,温度31.49℃;菌株4G为芽孢杆菌(Bacillus),革兰氏阴性菌,菌落圆形乳白色,可利用的碳源:D-纤维二糖,D-葡萄糖,D-麦芽糖,蔗糖,D-甘露醇,D-海藻糖等,最佳培养条件:盐度2.920%,pH 7.99,温度37.27℃。利用乙炔还原法测定二者的固氮酶活性,分别为252.21 nmol C_2H_4/(mL·h)和196.31 nmol C_2H_4/(mL·h)。研究证实两株菌株具有良好的固氮性能,可用于海草固氮肥的研制,在海草床生态系统恢复研究领域具有潜在的应用前景。     

Acclimation of Litopenaeus vannamei Postlarvae to Low Salinity: Influence of Age, Salinity Endpoint, and Rate of Salinity Reduction

Abstract.— Inland culture of Liropenaeus vannarnei in low salinity well waters is currently conducted on a small scale in a few areas in the U.S. To successfully rear shrimp in low salinity water, postlarvae (PL) must be transferred from high-salinity larval rearing systems to low-salinity growout conditions. To determine effective transfer methods, a series of experiments were conducted under controlled conditions to evaluate the influence of PL age, rate of acclimation, and salinity endpoint on 48 h survival of shrimp. Three age classes of L. vannurnei PL (10, 15, and 20-d) were acclimated from a salinity of 23 ppt to treatment endpoint salinities of 0, 1, 2, 4, 8, and 12 ppt. Survival of PL₁₀ acclimated to 0, 1, or 2 ppt salinity was significantly lower than survival of PL acclimated to salinities of 4, 8, and 12 ppt. Survival of PL, and PL₂₀ shrimp was only reduced for the 0 ppt salinity treatment, thus indicating a clear effect of age on salinity tolerance. The same age classes of PL were acclimated from 23 ppt to final salinity endpoints of I or 4 ppt at three different rates of salinity reduction: low, 19%/h; medium, 258/h, and high, 478/h. Survival was not significantly influenced by the acclimation rates for any of the three PL age classes. As in the fixed rate experiments, survival of the 10-d-old PL was significantly lower for shrimp acclimated to the 1 ppt endpoint compared to the 4 ppt endpoint. Under the reported conditions, age appears to influence PL tolerance to a salinity end-point. A 10-d-old PL can be acclimated to 4 ppt with good survival, whereas 15- and 20-d-old PL can be acclimated to a salinity of 1 ppt with good survivals.