褶纹冠蚌钩介幼虫非寄生变态发育观察及早期稚蚌的生长

为揭示褶纹冠蚌钩介幼虫变态发育特征及过程,采用体外培养方法实现了褶纹冠蚌钩介幼虫的非寄生变态发育。运用光学显微镜和扫描电子显微镜对变态发育过程中幼虫外部形态、内部器官发育进行了系列观察,对非寄生变态发育的稚蚌后期生长发育进行跟踪研究,并分析了底泥和光照两种环境因子对稚蚌存活及生长的影响。结果显示:在整个培养过程中,钩介幼虫的外部形态及大小未出现显著性变化,而斧足、鳃丝、外套膜及内脏团等组织器官逐步形成;在培养第3天,幼虫可见斧足雏形,鳃丝、外套膜纤毛尚未发现;在培养第6天,斧足成形,可见斧足侧沟,外套膜纤毛稀疏,鳃丝出现;培养第9天,斧足纤毛、外套膜纤毛增多,鳃丝密集。稚蚌投喂30d后,鳃丝基本成形。养殖试验结果表明:底泥对稚蚌存活和生长具有显著影响（P < 0.01）,而光照无显著性影响（P>0.05）。该结果为蚌科钩介幼虫变态发育生物学研究积累了基础资料,也通过对稚蚌生长的评估证实了体外培养是蚌类人工繁育及保护的有效技术途径。     

大竹蛏胚胎发生及稚贝发育研究

在人工培育条件下,对大竹蛏(Solen grandis)胚胎发生及稚贝发育进行显微观察,探究大竹蛏胚胎及幼虫发育规律。结果表明,大竹蛏胚胎及幼虫发育过程为：受精卵、卵裂、囊胚期、原肠期、担轮幼虫、D形幼虫、稚贝。在水温为22.4℃时,受精后20~24h发育成D形幼虫,5~7d变态为稚贝,38d稚贝贝壳已具备成贝形态,壳长壳高比为2.60。从受精卵到附着所需积温为3088.79~5005.19℃?h。稚贝先形成出水管后形成进水管,最终形成“一管双孔”。壳长与壳高关系式为     

饥饿和再投喂对青蛤(Cyclina sinensis)幼虫生长、存活及变态的影响

在温度18.2～20.6℃,盐度23～25,pH 7.96～8.14 的条件下,研究了饥饿和再投喂对青蛤幼虫生长、存活及变态的影响.结果表明:在饥饿状态下,幼虫具有生长现象,且随着饥饿时间的延长,壳长逐渐接近一个常值而不再生长;幼虫可以由面盘幼虫发育到足面盘幼虫.随饥饿时间延长存活率下降;且足面盘幼虫及其变态规格、单水管稚贝规格随着饥饿时间延长而减小;幼虫的不可逆点(PNR)为12.48d;延迟变态时间长达12.7d.饥饿后再投喂相同的时间,幼虫能够恢复生长,存活的幼虫能够变态;稚贝表现出补偿生长现象,以壳长作为衡量标准,完全补偿生长能力依次为:S10＞S11＞S12＞S1＞S2＞S3;超补偿生长能力依次为:S9＞S8＞S7＞S6＞S5＞S4.     

大竹蛏胚胎发生及稚贝发育基本特征

在人工培育条件下,对大竹蛏(Solen grandis)胚胎发生及稚贝发育进行显微观察,探究大竹蛏胚胎及幼虫发育规律。结果表明,大竹蛏胚胎及幼虫发育过程为:受精卵、卵裂、囊胚期、原肠期、担轮幼虫、D形幼虫、稚贝。在日平均水温为22.4℃时,受精后20～24 h发育成D形幼虫,5～7 d变态为稚贝,38 d稚贝已具备成贝形态,壳长壳高比为2.60。从受精卵到附着所需积温为3 088.79～5 005.19℃.h。稚贝先形成出水管,后形成进水管,最终形成"一管双孔"。壳长与壳高关系式为y=150.37e0.002 7 x,x为壳高(μm),y为壳长(μm),R2=0.985 5,P0.01;壳长与日龄关系式为y=143.38e0.091 6 x,x为日龄(d),y为壳长(μm),R2=0.979 5,P0.01;壳高与日龄关系式为y=33.979 x-15.450,x为日龄(d),y为壳高(μm),R2=0.987 3,P0.01。     

温度和盐度对青蛤孵化及幼虫、稚贝存活与生长变态的影响

在9个温度梯度(10-34℃)和10个盐度梯度(盐度3‰-50‰)条件下,研究了温度和盐度对青蛤孵化及幼 虫、稚贝生存与生长变态的影响。结果表明,青蛤孵化和浮游幼虫生长的适温范围为24-32℃,最适温度均为26- 30℃,稚贝生长的适温范围为22-32℃,最适温度为24-30℃。在最适温度下,D形幼虫变态率达80．7％-88．2％, 浮游幼虫和稚贝的存活率分别为86．2％-88．7％和81．5％-84．0％;孵化及浮游幼虫的生长适宜盐度为15‰- 30‰,稚贝为10‰-35‰,最适盐度均为20‰-25‰。在最适盐度下,D形幼虫的成活率、变态率、生长速度皆最高, 分别达到86．9％、77．5％和9．38×11．0μm/d,匍匐幼虫经14-14．5d发育至双管期稚贝,至双管期稚贝的成活率 82．5％-85．0％,日平均生长达13．1μm以上。与大多数滩涂贝类一样,青蛤属于广温广盐性贝类,且稚贝对低盐的 适应能力强于对高盐的适应能力。     

绢丝丽蚌寄生变态发育的研究

绢丝丽蚌钩介幼虫在雌蚌外鳃中发育成熟后于冬季排放到体外,而后寄生到宿主鱼的鳃丝进行变态发育,寄生期历时近4个月.寄生后3d,内、外足丝消失;35d后,肉足形成;90d后,肠、闭壳肌、肾脏和鳃原基等生成;壳面加厚且外凸.次年春季,钩介幼虫变态发育成大小为253.37×273.26×179.96μm的稚蚌,脱离鱼鳃营独立生活     

香港巨牡蛎和长牡蛎幼虫及稚贝的表型性状

为了评估香港巨牡蛎和长牡蛎在北方沿海的早期表型性状,于2010年7月,以2009年6月在青岛繁育的两种牡蛎为材料,在大连研究了温度(Mt:(22±1.0)℃及Ht:(28±1.0)℃)、盐度(S₂₀:20±1.0及S₃₀:30±1.0)及中间育成环境(ID:室内及OD:室外)对两种牡蛎幼虫及稚贝表型性状的影响。结果表明:香港巨牡蛎壳宽显著大于长牡蛎(P<0.05),壳高及怀卵量显著小于长牡蛎(P<0.05),壳长、鲜重及壳重两者间无显著差异(P>0.05)。在温度和盐度相同情况下,长牡蛎卵径、受精率、孵化率及D形幼虫均大于香港巨牡蛎;香港巨牡蛎幼虫浮游前期生长较慢,而后快于长牡蛎。两种牡蛎幼虫存活能力在15日龄时高温组>中温组;相同温度下,香港巨牡蛎中盐组>高盐组,长牡蛎高盐组>中盐组。幼虫变态期间,较低的温度延迟了变态时间,降低了变态率,使得两种幼虫变态规格大型化。温度是影响幼虫生长、存活、变态的最主要因素,其次为盐度,交互作用几乎尚未起到作用。中间育成阶段,室外比室内培育效果更好,且香港巨牡蛎稚贝壳高在60日龄以后显著大于长牡蛎(P<0.05),环境是影响稚贝生长的最主要因素;无论室内还是室外两种牡蛎稚贝的存活率均在90%以上,且各实验组间无显著差异(P>0.05)。     

盐度对墨西哥湾扇贝幼虫和稚贝生长与存活的影响

2000年4月和2001年4月在浙江省玉环县抛西水产育苗场研究了海水盐度对墨西哥湾扇贝浮游幼虫和稚贝生长和存活的影响。结果表明：浮游幼虫的适宜盐度为16．54—36．58,最适生长盐度为23．38—30．02;稚贝的适宜盐度为23．38—42．70,最适生长盐度为23．38—36．58。     

婆罗囊螺早期发育的初步研究

描述了婆罗囊螺(Retusa borneensis)从受精卵到幼虫孵化后的发育过程,婆罗囊螺为雌雄同体的一年生贝类,在浙江沿海繁殖期是6∽9月,盛期在7∽8月。婆罗囊螺为体内受精种类,胚胎发育过程为变态发育,可以分为卵裂、囊胚、原肠胚、担轮幼虫和面盘幼虫等几个阶段。个体发育从受精卵的卵裂开始,卵裂为螺旋形的全裂。卵裂不断进行,囊胚形成,后以外包和内陷方式共同形成了原肠胚。婆罗囊螺的面盘幼虫在膜内就已经形成,并且具备运动能力,但是其面盘和纤毛远没有膜外面盘幼虫发达。幼虫浮游一段时间后,就营匍匐生活,然后变态发育为稚贝。本文还就婆罗囊螺的繁殖期、繁殖力、交配产卵和繁殖特性等做了进一步的讨论。     

大蒜对菲律宾蛤仔早期生长发育的影响

实验了不同大蒜汁浓度(0、2、4、8、16、32 mg/L)对菲律宾蛤仔受精卵孵化率,幼虫生长、存活、变态及稚贝生长与存活的影响,总结了室内大规模人工育苗过程中大蒜防病效果。结果表明:随着大蒜汁浓度的增加,孵化率降低;大蒜汁浓度达到16mg/L,胚胎发育延迟;达到32mg/L,受精卵不能孵化为正常幼虫。浮游期间,幼虫的生长受大蒜汁抑制,幼虫的存活率则随着大蒜汁浓度增加先升高后降低;幼虫的变态率随着大蒜汁浓度的增加先升高后降低,以16mg/L为最适浓度;变态规格随着大蒜汁浓度增加而减小。室内培育期间,稚贝生长与存活随着大蒜汁浓度的增加先升高后降低,以8mg/L为最适浓度;室内大规模人工育苗过程中,使用浓度为8-10mg/L大蒜汁可以起到较好的防病效果。     

Potential role of cathepsin B in the embryonic and larval development of clam Meretrix meretrix

This study was designed to investigate the possible role of Meretrix meretrix cathepsin B (MmeCB) in embryonic and larval development. MmeCB mRNA expression profile was revealed by semi-quantitative RT-PCR. The level of MmeCB mRNA expression was low in trochophore stage but high in pedveliger stage. MmeCB protein expression was detected in the digestive gland, velum, and epidermis along the edges of the shell in D-larvae and pedveligers by immunocytochemistry. In post larvae, MmeCB protein expression was noticed abundant in the digestive gland, whereas a modest expression was identified in the gill filament. The average shell length of larvae hatched from embryos treated with 0.01, 1, and 10?μmol/L Ca074Me (a cathepsin B inhibitor) was significantly shorter than that of control groups. The metamorphosis rates of larvae treated with 0.01 and 1?μmol/L Ca074Me were significantly lower than that of control groups in 4-day larvae, but not in 5-day larvae. Taken together, these results indicated that MmeCB may have stimulatory effects on embryonic development, metamorphosis, and larval growth during M. meretrix larval development.     

Investigation of early mussel (Perna canaliculus) development using histology,SEM imaging,immunochemistry and confocal microscopy

A comprehensive study, incorporating histology, light microscopy, scanning electron microscopy, immunochemistry and confocal microscopy, was performed to investigate embryogenesis and larval development of the New Zealand Greenshell? mussel, Perna canaliculus. Detailed observations with this multi-technique approach revealed a gastrula stage at 18 hours post-fertilization, with the appearance of a blastopore, apical sense organ and enclosing vegetal pole. Early D-stage larvae showed limited alimentary organogenesis and clear initiation of a developing nervous system. Shell morphology of D-larvae was characterized by a flat, hinged, pitted–punctate prodissoconch I shell, followed closely by commarginal growth lines within the prodissoconch II shell. Early umbo larvae had a protruding functioning velum, and well-developed posterior adductor and velar retractor muscles. Significant progression in neuronal development occurred just before the umbo stage with noticeable paired cerebral, pedal and visceral ganglia. Shell morphology was characterized by further prodissoconch II secretion with a more rounded umbonate appearance. During the transition through the pediveliger stage, rapid development of the gill rudiment, eye spot and functioning foot was observed with ongoing neuronal development. The first appearance of the dissoconch shell layer took place during this transition, at which point the nervous system was highly distinct with innervations extending throughout muscle regions and between ganglia. This study provides the first comprehensive documentation of the developmental stages of P. canaliculus larvae from fertilization to settlement. The study highlights the advantages of using a combination of techniques to understand larval development and provides crucial information to identify larval performance during larval rearing.     

Véligère planctotrophe du doridien Aegires punctilucens (D'Orbigny) (Mollusca: Nudibranchia: Notodorididae): Description et métamorphose

Different larval planktonic stages of the nudibranch Aegires punctilucens (D'Orbigny) are described. The youngest has a shell of the protoconch type 1 (Thompson) and a bilobed velum. After loss of the shell, the next stage is characterized by a large velum with broad and thick lobes. The mantel covers the body and has tubercles which grow progressively. Spicules appear in the mantle and in the foot; they are simple, triradiate or cross-shaped. A zone of hyaline denticles are present in the stomach lumen.Metamorphosis has been obtained under laboratory rearing. After the gradual resorption of the velum, the animal looks like a small dorid and is grey with white spots. The foot is slender and there are 14 tubercles always arranged in the same way and bristled with spicules.After discussing the species identification, the veliger is compared with other nudibranch larvae. The development of Aegires is very unusual with a two-stage metamorphosis, the first at the time of loss of the shell, and the second at loss of the velum cast. The intermediate stage between those two stages is planktonic.     

GENETIC CORRELATIONS AMONG MORPHOMETRIC TRAITS AND RATES OF GROWTH AND DIFFERENTIATION IN THE GREEN TREE FROG,HYLA CINEREA

It is often proposed that the morphometric shape of animals often evolves as a correlated response to selection on life-history traits such as whole-body growth and differentiation rates. However, there exists little empirical information on whether selection on rates of growth or differentiation in animals could generate correlated response in morphometric shape beyond that owing to the correlation between these rates and body size. In this study genetic correlations were estimated among growth rate, differentiation rate, and body-size-adjusted head width in the green tree frog, Hyla cinerea. Head width was adjusted for size by using the residuals from log-log regressions of head width on snout-vent length. Size-adjusted head width at metamorphosis was positively genetically correlated with larval period length. Thus, size-independent shape might evolve as a correlated response to selection on a larval life-history trait. Larval growth rate was not significantly genetically correlated with size-adjusted head width. An additional morphometric trait, size-adjusted tibiofibula length, had a nonnormal distribution of breeding values, and so was not included in the analysis of genetic correlations (offspring from one sire had unusually short legs). This result is interesting because, although using genetic covariance matrices to predict long-term multivariate response to selection depends on the assumption that all loci follow a multivariate Gaussian distribution of allelic effects, few data are available on the distribution of breeding values for traits in wild populations. Size at metamorphosis was positively genetically correlated with larval period and larval growth rate. Quickly growing larvae that delay metamorphosis therefore emerge at a large size. The genetic correlation between larval growth rate and juvenile (postmetamorphic) growth rate was near zero. Growth rate may therefore be an example of a fitness-related trait that is free to evolve in one stage of a complex life cycle without pleiotropic constraints on the same trait expressed in the other stage.     

Larval development of the invasive charru mussel,Mytella strigata (Bivalvia: Mytilidae)

ABSTRACT

The South American charru mussel, Mytella strigata, was recently recorded in Singapore waters, possibly introduced into Southeast Asia through shipping. The mussels have rapidly spread across estuarine coastal mudflats. Adult mussels were collected, spawned in aquaria and larvae were successfully cultured to the juvenile stage in the laboratory. The larval morphology and development of M. strigata is described in this paper. D-shaped veligers were produced within 20 h of fertilization and were approximately 75 µm in shell length. These larvae were capable of settlement two weeks post fertilization. Given an adequate amount of food, they were able to grow up to 1 mm in shell length within 30 days. The larval shell of M. strigata possesses anterodorsal G2 hinge teeth as distinct wavy ledges, with a pitted resilial ridge clearly evident in the juvenile shell.     

Relationships between larval nutritional experience, larval growth rates, juvenile growth rates, and juvenile feeding rates in the prosobranch gastropod Crepidula fornicata

Planktonic larvae experiencing short periods of starvation or reduced food supply often grow and develop more slowly, have poor survival, fail to metamorphose, metamorphose at smaller sizes, or grow slowly as juveniles. In this study, we examined the impact of short periods of food limitation at various stages of larval development on larval and juvenile growth in Crepidula fornicata. In addition, we considered whether juveniles that were stressed as larvae grew poorly because of reduced rates of food collection due to impaired gill function. For 5 experiments, larvae were either starved for several days beginning within 12 h of hatching or were starved for the same number of days following 1 or more days of feeding at full ration (cells of the naked flagellate Isochrysis galbana, clone T-ISO, at 18×10⁴ cells ml⁻¹). In one experiment, larvae were transferred for 2 or 4 days to seawater with extremely low phytoplankton concentration (1×10⁴ cells ml⁻¹). In all experiments, larvae were returned to full ration following treatment. Control larvae were fed full ration from hatching to metamorphosis. When larvae reached shell lengths of about 900 μm they were induced to metamorphose and then reared individually at full ration in glass bowls, with phytoplankton suspension replenished daily. Larval and juvenile growth rates were determined by measuring changes in shell length (longest dimension) over time. Juvenile feeding rates were determined by monitoring changes in phytoplankton concentration over 2–3 h at the end of the growth rate determinations. In general, larval growth rates for the first 2 days after the resumption of feeding were inversely proportional to the length of time that larvae were starved. However, larval growth rates ultimately recovered to control levels in most treatments. Starving the larvae caused a significant reduction in initial juvenile growth rates (first 3–4 days post-metamorphosis) in most experiments even when larval growth rates had recovered to control levels prior to metamorphosis. Juvenile growth rates were not significantly reduced when larvae were subjected to reduced food availability (1×10⁴ cells ml⁻¹), even for treatments in which larval growth rates were compromised. Mean weight-specific filtration rates for juveniles were significantly reduced (p<0.05) following larval feeding experience in only one or possibly 2 of the 4 experiments conducted. Our data suggest that although larvae of C. fornicata may fully recover from early nutritional stress, the resulting juveniles may exhibit poor initial growth due to impaired gill function, reduced digestive capability, or reduced assimilation efficiency.     

Laboratory culture of the larvae of Conus textile Linné (Gastropoda: Toxoglossa)

The larvae of the Indo-Pacific gastropod Conns textile Linné were reared in the laboratory from hatching through metamorphosis. Larvae fed a mixed phytoplankton culture of Isochrysis galbana and Phaeodactylum tricornutum grew at a rate of 0.06 mm/day and began metamorphosing 16 days after hatching. Unfed control cultures yielded no metamorphically competent larvae. Laboratory-reared larvae metamorphosed spontaneously on the walls of the fïberglass rearing tanks when their average shell length was 1.5 mm. Measurements made on field-collected Conns textile juveniles indicate that the larvae metamorphose at the same size in the laboratory as they do in nature.Rates of larval shell length increase and dry weight increase paralleled each other until metamorphosis. At this point, shell growth slowed while dry weight increased suddenly. It is suggested that this weight increase reflects calcification and strengthening of the fragile larval shell upon entering the benthic environment.     

Growth during the early life history of the Pacific tarpon,Megalops cyprinoides

The early growth of the Pacific tarpon,Megalops cyprinoides, was studied by larval otolith analysis and rearing of larvae and juveniles in the laboratory. Morphology of the sagitta, validation of sagittal daily increments, age at the start of metamorphosis, decrement of standard length in early metamorphosis, and growth under rearing conditions are described. The sagitta of fully-grown Pacific tarpon leptocephali were transparent and circular, with regular intervals between the neighboring rings becoming wider at the onset of metamorphosis. Alizarin complexone treatment of larvae confirmed the daily formation of the sagittal rings. Metamorphosis was estimated to start about one month after hatching. After drastic shrinkage during the first several days of metamorphosis, the body length more or less stabilized for one month and then resumed rapid growth. The early growth of Pacific tarpon was divided into four phases as follows: A) leptocephalus positive growth phase; B) leptocephalus negative growth phase; C) sluggish growth phase; and D) juvenile growth phase.     

The influence of temperature on growth rate and length of larval life of the gastropod, Crepidula plana Say

The relationship between rate of larval development and the potential to prolong larval life was examined for larvae of the marine prosobranch gastropod Crepidula plana Say. Larvae were maintained in clean glass dishes at constant temperatures ranging from 12–29°C and fed either Isochrysis galbana Parke (ISO) or a Tahitian strain of Isochrysis species (T-ISO). Under all conditions, larvae grew at constant rates, as determined by measurements of shell length and tissue biomass. Most larvae eventually underwent spontaneous metamorphosis. Regardless of temperature, faster growth was associated with a shorter planktonic stage prior to spontaneous metamorphosis. Within an experiment, higher temperatures generally accelerated growth rates and reduced the number of days from hatching to spontaneous metamorphosis. However, growth rates were independent of temperature for larvae fed ISO at 25 and 29°C and for larvae fed T-ISO at 20 and 25°C. Where growth rates were unaffected by temperature, time to spontaneous metamorphosis was similarly unaffected. Maximum durations of larval life at a given temperature were shorter for larvae of Crepidula plana than for those of the congener C. fornicata (L.), although both species grew at comparable rates. Interpretations of the ecological significance of these interspecific differences in delay capabilities will require additional data on adult distributions and larval dispersal patterns in the field.