四种大型水母横裂生殖的差异与其种群数量变动的初探

在实验室培养了4种大型水母:海蜇、海月水母、白色霞水母及沙海蜇的螅状体.在相同的生态环境下,观察了这4种螅状体的横裂生殖, 其横裂生殖率:海蜇100%、海月水母100%、白色霞水母0%、沙海蜇0%.经过横裂生殖螅状体的存活率:海蜇20%、海月水母100%.未横裂生殖螅状体的存活率为100%,同时探讨了这4种大型水母的种群数量变化原因.     

温度、盐度和光照对海蜇足囊繁殖的影响

在实验室条件下，就温度、盐度和光照对海蜇（Ｒｈｏｐｉｌｅｍａｅｓｃｕｌｅｎｔａｋｉｓｈｉｎｏｕｙｅ）足囊形成和萌发的影响进行观察。温度实验在０～３０℃范围内设７组，盐度实验在２～３２．１‰范围内设１６个梯度，光照分为自然光和黑暗两组。实验显示：１０℃以上海蜇无足囊繁殖迹象，１５～３０℃范围内，随温度升高，海蜇足囊繁殖能力增强；６‰以下盐度，海蜇不能进行足囊繁殖，２０～２２‰是海蜇足囊繁殖的最适盐度；黑暗有利于足囊繁殖。温度是足囊繁殖的关键因子，盐度和光照是足囊繁殖的充分条件。作者认为，适宜的环境因子是海蜇螅状体形成的必要条件，尽管足囊可以抵御外界的恶劣环境，但足囊形成并非需要不良环境因子诱导，足囊繁殖是海蜇螅状体一种正常的无性繁殖方式     

不同环境对海蜇螅状幼体足囊繁殖和横裂生殖影响的研究

研究了不同温度,光照条件对海蜇螅状体生长及足囊繁殖和横裂生殖的影响。结果表明,适宜的营养和环境条件有利于海蜇螅状体足囊繁殖,2组实验中螅状幼体出现横裂的个数均随实验天数的增加有增长趋势。2组实验最后的横裂率分别达到83.33％和87．50％;形成4-6个碟状体的螅状幼体在Ⅰ、Ⅱ组中所占比例均在50％左右;Ⅰ组横裂过程经历时间集中在4—6天,Ⅱ组横裂过程经历时间多为2～4天。横裂释放完毕之后在最后一个裂节下方的亲本螅状体再生的触手数目可基本确定为8个,由8触手到16触手的转变过程中长势显著。     

温度对海月水母横裂生殖的影响研究

近年来灾害性海月水母种群数量在东亚海域内大幅度增加,对渔业资源及海洋生态系统造成严重灾害。横裂生殖可以使海月水母螅状体释放小水母(碟状幼体),而这一过程会扩增成体水母的种群数量。为探明温度对海月水母横裂生殖的影响,将源自日本濑户内海的海月水母螅状体由25℃分别转移至9、12、14、16、18℃5个较低的温度下,并在饥饿和黑暗状态下监测90 d。试验结果显示,横裂开始时间(或预横裂时间)、横裂率和横裂持续时间均受温度影响,平均预横裂时间在12、14℃下最短,横裂率在9、12℃下最高(约65%),横裂持续时间在较高的温度下比较短。每只螅状体所释放的平均碟状幼体数量在各温度下差异显著,14℃时最高。通过本试验验证,海月水母最适的横裂生殖温度为12～14℃,在此温度范围内海月水母横裂生殖开始的最快,并且发生横裂生殖的螅状体比例更大。据研究结果推断,暖冬可能会导致日本濑户内海下一年度海月水母的种群数量大幅度增加。     

环境因子对海蜇早期幼体发育影响的生态学研究进展

海蜇是经济价值很高的大型食用水母,历来是我国沿岸渔业的重要捕捞对象。本文综述了营养条件、温度、盐度、光照、溶氧、重金属、pH、氨氮对海蜇足囊繁殖与横裂生殖以及螅状体与碟状体生存的影响,对海蜇早期幼体发育的研究进展情况进行了概述。总结发现:环境因子对海蜇幼体发育影响的作用机理有待进一步探讨,环境突变对海蜇横裂生殖的影响以及海蜇碟状体到水母体系统发育过程的研究尚需补充完善。     

营养条件对海蜇螅状体形成足囊及足囊萌发的影响

用卤虫(Artemia)无节动体作为海蜇(Rhopilema esculenta)螅状幼体的饵料,按不同投饵频次划分为7个营养水平,考察不同营养水平对海蜇螅状体形成足囊及足囊萌发的影响。结果表明,营养条件不仅对螅状体形成足囊的数量有直接影响,而且对足囊萌发也有明显的间接影响。在具备丰富的营养条件下,螅状体形成足囊活跃,个体大,易于萌发;缺乏营养则抑制足囊形成,即使形成足囊,个体也小,不萌发或萌发率很低。     

高温和投饵对海蜇螅状幼体生长和足囊繁殖的影响

以海蜇新生螅状幼体为研究对象,采用实验生态学方法研究3种高温(室内恒温、夏季常温、夏季高温)、3种饵料投喂频率(无饵料投喂、每7 d投喂1次、每2 d投喂1次)及其交互作用对海蜇螅状幼体的死亡率、个体生长和足囊繁殖的影响,试验持续45 d。试验结果显示：高温条件下,饵料投喂频率显著影响海蜇螅状幼体的死亡率(P<0.05);而高温、饵料投喂频率及两者交互作用均显著影响海蜇螅状幼体的相对生长率(P<0.05);各高温组中螅状幼体生成的足囊数均随饵料投喂频率的增加而增多;足囊萌发率最多出现在夏季常温-每7 d投喂1次组,平均为34.34%;饵料投喂频率对海蜇螅状幼体生成足囊数及足囊萌发率影响显著(P<0.05),高温及两者交互作用对海蜇螅状幼体生成足囊数及足囊萌发率影响均不显著(P>0.05)。试验结果表明,尽管高温条件下海蜇螅状幼体死亡率高,但存活的螅状幼体足囊繁殖速度快,足囊繁殖速度随温度的升高而加快可能是螅状幼体应对高温死亡率增加的一种繁殖策略。试验结果可为提高海蜇育苗技术和准确预报苗种产量提供科学依据。     

咖啡金黄水母的人工培育及生活史观察

以日本白令海引进的咖啡金黄水母为亲本,通过人工繁殖的方法获得受精卵.在实验室培育条件下,对浮浪幼虫、螅状体、碟状体和水母幼体等多次变态发育过程进行了系统观察,描述了各发育阶段形态变化,首次报告了咖啡金黄水母的生活史.咖啡金黄水母为体外受精,卵为沉性,受精后6h内发育为浮浪幼虫,浮浪幼虫有明显的趋光性,在54 h内变态附着为4触手螅状体.螅状体能通过多种方式进行无性繁殖,于20℃横裂生殖,每个螅状体每次横裂产生8～21个碟状体,碟状体的数量和质量与横裂前螅状体的状态有关.合适的水流和充足的食物保证了碟状体在60 d内变态为伞径10cm的育成体.人工条件下,螅状体可长期保存,水母体能饲养8～10个月.     

安朵仙水母生活史的实验观察

安朵仙水母在固着的无性繁殖螅状体和浮游的有性繁殖水母体间交替,其生活史中绝大多数环节并不是自发进行的,而是受特定的物理、化学或生物因素的影响。静止水流和雌雄个体间的交互作用对于产卵和受精是非常重要的,受精卵在64h内可经浮浪幼虫阶段变态为4触手螅状体。螅状体能通过单碟型横裂产生水母体,但对温度和光照要求严格。出芽生殖是螅状体无性繁殖的唯一方式,出芽率与温度关系最为密切。大多数碟状体在横裂的过程中生长出口腕,并在脱离螅状体12～24h内翻转为口腕向上、外伞向下的倒立形态。水母体可通过食物和体内的共生藻获得能量。人工条件下,螅状体可长期保存,水母体可以饲养两年以上。     

温度、盐度和光照对海蜇足囊萌发的影响

形成足囊是海蜇(Rhopilema esculenta Kishinouye)螅状幼体无性生殖的方式。但已形成的足囊,有的可萌发为新的螅状幼体,有的则不萌发乃致死亡。为探讨足囊的萌发机制,了解海蜇在自然条件下的种群数量变动规律,作者首先就温度、盐度和光度等环境因子对足囊萌发的影响进行观察,温度实验在0°—30℃范围内分7组,实验结果表明:10℃以下(包括℃)足囊不萌发;15℃—30℃范围内,足囊萌发率随温度升高而增加,25℃和30℃时足囊萌发率最大,为23.33%(实验进行22天)。盐度实验是在20°±1℃温度下,在盐度2～32.1‰范围内分16个梯度,每梯度又分别设黑暗与自然光两种光度水平,实验结果表明,盐度在8‰以下(包括8‰)足囊死亡,足囊萌发的最适范围为18～22‰,在盐度为22‰黑暗条件下,足囊萌发率最高为43.33%(实验进行24天),黑暗有利于足囊萌发。     

褐藻羊栖菜繁殖生物学特征和生活史流程的补充研究

以温州市洞头区人工养殖羊栖菜和野生羊栖菜为研究样本,详细描述了羊栖菜成熟孢子体有性生殖,假根与侧生枝无性生殖的繁殖生物学特征和生活史流程。详细记录了羊栖菜卵、精子和受精卵的减数分裂和有丝分裂过程,假根、茎(主茎和侧生茎)、叶(气囊)和生殖托(雌托和雄托)等4类器官生长、发育和分化过程,胚、幼孢子体和成熟孢子体形态结构特征。在此基础上对现有羊栖菜繁殖生物学特征及生活史流程进行了补充和修正,增加了羊栖菜侧生枝无性生殖和羊栖菜幼孢子体期有性生殖的相关内容,并重新绘制了羊栖菜生活史流程图。该研究结果将为开展羊栖菜养殖生态学研究,深层次解析羊栖菜生殖节律、种群繁衍与环境关系奠定基础。     

白色霞水母各发育阶段的形态

对白色霞水母从受精卵到成体水母各发育期的形态进行了描述。受精卵发育成带纤毛的浮 浪幼虫，浮浪幼虫在定置前形成一种凸面的圆形浮浪幼体囊, 经脱囊狭窄柄部拉长进而变成一个细长颈瓶形状，萌发出4个触手成为早期螅状体；螅状体可产生足囊和通过产生匍匐茎形成囊胞进而发育成新的螅状体；横裂为典型的单碟型横裂；新释放的碟状幼体绝大多数为8个缘叶，8个感觉棍和8对钝圆的缘瓣，但畸形个体最多12个，最少6个缘叶，同时对海蜇与白色霞水母的碟状幼体形态进行了比较。成体水母伞径200～300 mm，大型个体超过500 mm。外伞表面光滑,近中央的伞顶上有许多密集的刺胞丛隆起, 8个缘叶，8个感觉棍,口腕非常发达，口腕上有大量刺细胞团。可根据感觉胃囊和触手囊是否连接、缘瓣水管的排列类型、外伞顶中央是否有刺细胞丛以及个体伞径和颜色对白色霞水母、发形霞水母、棕色霞水母和紫色霞水母进行鉴别。     

基于人工神经网络的日本海舍氏贝乌贼角质颚色素沉积特性分析

根据中国鱿钓船于2018年12月在日本海采集的303个舍氏贝乌贼样本,进行基础生物学分析,对其角质颚色素沉积等级进行划分和判定,利用人工神经网络模型分析色素沉积等级与胴长、体质量、性腺成熟度、角质颚形态参数和胃级的关系,并对各生长因子的中位数进行线性拟合。结果显示,胴长对角质颚色素沉积的贡献率最大,为22.90%,其次分别为下头盖长、性腺成熟度、体质量、下喙长和下翼长,贡献率分别为16.50%、14.40%、11.90%、11.70%和11.60%,下侧壁长和胃级对角质颚色素沉积的贡献率较小,分别为6.30%和4.70%。舍氏贝乌贼角质颚的色素沉积与胴长、体质量、性腺成熟度和胃级这4项生长因子的关系均不存在性别间显著性差异。角质颚色素沉积等级与胴长、体质量和角质颚外部形态参数均呈正相关,并随着性腺成熟度的增加而增加,但与胃级的线性关系不明显。研究表明,日本海舍氏贝乌贼角质颚色素沉积等级与胴长、性腺成熟度、体质量和角质颚形态参数均呈正相关关系,可以利用胴长、性腺成熟度、体质量和角质颚形态参数预估色素沉积等级。     

Predation on fish larvae by moon jellyfish <Emphasis Type="Italic">Aurelia aurita</Emphasis> under low dissolved oxygen concentrations

ABSTRACT:   Laboratory experiments were conducted to test the hypothesis that low dissolved oxygen concentrations have the potential to enhance the predation rate on fish larvae by moon jellyfish Aurelia aurita which is increasing in abundance in the coastal waters of Japan. Larvae of the red sea bream Pagrus major in four size classes (2.9, 4.1, 6.2 and 8.6 mm in standard length) were used as prey in a short-term predation experiment. No change in the bell contraction rate of the jellyfish (mean bell diameter, 100.4 ± 10.2 mm) was observed at the oxygen concentrations tested (1, 2 and 4 mg/L, and air-saturated, 5.5–6.0 mg/L), suggesting a strong tolerance to a decline in the oxygen concentration. More than 80% of the 2.5 and 4.1-mm size-class larvae were predated on by the jellyfish at all oxygen concentrations during the 15-min trials in 10-L tanks. The 6.2 and 8.6-mm size-class larvae were able to escape from the jellyfish apparently due to their developed swimming ability at the two higher dissolved oxygen concentrations. There was an increase in predation on larvae of these two size classes at the two lower dissolved oxygen concentrations. Predation by moon jellyfish on fish larvae can be more intense at low dissolved oxygen concentrations that commonly occur in the coastal waters of Japan.     

Performance of a conical jellyfish exclusion device installed in a trawl net

Recently, the increasing population of giant jellyfish Nemopilema nomurai has negatively affected coastal fisheries in Korea. As a result, the fishing industry has begun developing devices to prevent jellyfish capture. In this study, we assessed the performance of a conical jellyfish exclusion device in the coastal areas of Yokji Island in southern Korea during 2009. After hauling, we measured the length, diameter, and weight of the jellyfish and fish that were captured by the cod end and cover net. We found that the captured species included N. nomurai, silver croakers Pennahia argentata, yellow croakers Larimichthys polyactics, shotted halibut Eopsetta grigorjewi, largehead hairtails Trichiurus lepturus, and melon seeds Psenopsis anomala. The catch ratios of the giant jellyfish that entered the cod end in terms of weight ranged from 0.005 to 0.027. In contrast, the catch ratios of total fish in terms of weight and number were 0.793 and 0.835, respectively. On selectivity analysis of a conical separator for individual fish species, their exclusion ratios were independent of their length, and were similar to their observed exclusion ratios in terms of number. These results indicated that the conical jellyfish exclusion device performs well; however, some improvements are needed to minimize the escape of fish from the net.     

文蛤动态能量收支模型构建、验证与应用

为评估文蛤生态容量,实验根据动态能量收支理论,基于R语言构建了文蛤动态能量收支模型,采用线性与非线性回归法估算模型参数,通过对比围塘环境下文蛤壳长、湿重、软体部湿重的实测值与模拟值验证模型,并应用于模拟黄海海域滩涂区文蛤的生长过程。结果显示,文蛤模型主要参数形状系数、阿伦纽斯温度系数和单位体积结构物质所需能量分别为0.57、9 278 K和2 056 J/cm³;实测与模拟的文蛤壳长、湿重和软体部湿重相关系数R²平均为0.996,模拟值与实测值的平均误差为3.58%;如东沿海区域6月实测文蛤软体部干重为0.48 g,壳长3.12 cm,模型模拟的软体部干重、湿重和壳长分别为0.476 g,6.6 g和3.2 cm。研究表明,实验构建的文蛤动态能量收支模型的准确度较高,可真实地反映出文蛤在自然水域中的生长过程,为评估文蛤生态容纳量及构建文蛤相关的生态系统模型提供科学参考。     

Effects of turbidity on survival of larval ayu and red sea bream exposed to predation by jack mackerel and moon jellyfish

We conducted laboratory experiments to examine the effects of turbidity on the survival of red sea bream Pagrus major and ayu Plecoglossus altivelis altivelis larvae when exposed to either visual (jack mackerel juveniles) or tactile (moon jellyfish) predators. The experiments were conducted in 30-l tanks with three different levels of turbidity obtained by dissolving 0, 50, or 300 ppm kaolin. Predators were introduced to the experimental tanks followed by larvae of either red sea bream (mean ± standard deviation 6.1 ± 0.3 to 11.4 ± 2.1 mm standard length) or ayu (6.6 ± 0.3 and 24.4 ± 1.8 mm). When exposed to jack mackerel, the mean survival rate of larvae was significantly higher in 300 ppm treatments compared with the other turbidity levels. When exposed to moon jellyfish, however, there was a less marked difference in the survival rates among different turbidity treatments. Survival rates of ayu larvae exposed to moon jellyfish were generally lower than those of red sea bream. Our study indicates that anthropogenic increases of turbidity may increase the relative impact of jellyfish predation on fish larvae.     

Using otolith microchemical analysis to investigate the importance of brackish bays for pike (Esox lucius Linnaeus, 1758) reproduction in the southern Baltic Sea

The brackish Baltic Sea is inhabited by several primary freshwater fish species. The pike (Esox lucius) is the largest of these species and acts as the top predator in the marine food web of the Baltic Sea. Prior studies have shown the importance of brackish bays as spawning grounds for the Baltic Sea pike. To identify the spawning habitat of the pike population around the island of Rügen (southern Baltic Sea)—either freshwater streams flowing into the Baltic or brackish lagoons of the Baltic—we used the ICPMS method to quantify the strontium to calcium (Sr:Ca) ratios in sagittal otoliths of 79 adult pike. In total, only six per cent (n = 5) of the analysed Baltic Sea individuals were classified as being of freshwater origin. Ninety‐four per cent (n = 74) of analysed pike were classified as having hatched in brackish water. Compared to previous studies on Baltic Sea pike, our sample shows a high proportion of pike that is of brackish origin: this highlights the adaptive capacity of this species with regard to its ability to reproduce in different salinities. Our data highlight the importance of brackish bays for pike reproduction in the southern Baltic Sea, even if pike live on the upper limit of their salinity tolerance in this area. This is an important finding considering decreases in commercial catches in the last 30 years indicating a population decline supposedly related to recruitment failures.     

Nubbing of Coral Colonies: A Novel Approach for the Development of Inland Broodstocks

The establishment of large numbers of ramets from any individual coral genet can be used as a valuable source of material for the trade in ornamental marine organisms and in physiological and ecotoxicological studies. Here we discuss the rationale and the applicability of rearing ex situ large numbers of nubbins (minute fragments, down to the size of a single polyp). Nubbins taken from colonies of the branching Red Sea coral Stylophora pistillata show high survivorship under ex situ conditions and fast growth rates (5- to 6-fold increase in polyp numbers within 3 months) of the basal plates which revealed a significant correlation between tissue surface area and polyp numbers. Nubbins from branch tips and mid branches grew at a similar rate, but growth was affected by different light regimens. This approach requires further experimentation to elucidate optimal conditions.     

Efficacy of feeding tiger puffer Takifugu rubripes on moon jellyfish with respect to nutritional composition and behavioural traits

Although jellyfish blooms are serious nuisances for fisheries and other industries, the utilization and nutritional value of by‐catch jellyfish has drawn public attention. Here, we evaluated the efficacy of feeding tiger puffer Takifugu rubripes with moon jellyfish Aurelia sp. using 20‐day rearing experiments. Feeding on jellyfish had no positive effect on growth performance, although it significantly reduced neutral lipids and increased proportions of polar lipids, n?3 and n?6 highly unsaturated fatty acids (HUFAs), especially arachidonic and docosahexaenoic acids, and taurine. Supplemental feeding on jellyfish plus pellets elevated activity and responsiveness in the fish, with no effect on burst swimming speed or prevention of aggressive biting by siblings. The present research suggests that feeding on jellyfish improves body composition and some behaviours in tiger puffers. As cultured fish tend to accumulate excessive amounts of lipids from lipid‐rich pellets that can induce an unhealthy condition, and behavioural deficits of hatchery‐reared fish reduce survival after release in the wild, we propose the use of jellyfish as a supplemental diet in the nursery production of tiger puffer. Moreover, feeding on jellyfish can overcome deficiencies in alternative soy‐material feeds by supplying phospholipid, HUFAs, or taurine.