Increasing the stocking density in Paracentrotus lividus larviculture: Effects on survival and metamorphosis rates

The development of sustainable methods for sea urchin juvenile production is currently constrained by high mortality rates during larval growth and the high costs of larval rearing systems management. With the aim of developing a method for the production of juveniles of the purple sea urchin Paracentrotus lividus in a medium‐scale recirculating system, the present study focused on the effects of high stocking densities on larval growth. Plutei larvae were reared at three different densities (up to 7 ind/ml) in a semi‐static culture system. Larval survival and metamorphosis success were evaluated in order to identify the most effective density range. The highest metamorphosis rates (80%–95%) were obtained at 4 and 7 larvae/ml. These results are comparable with (and in some cases higher than) those reported for the same species at much lower larval densities. In conclusion, the rearing conditions tested here show for the first time that a significantly higher (4 ind/ml) stocking density than those of traditional P. lividus rearing methods (based on large volumes and low densities) can be adopted, thus supporting the feasibility of an increase in the final output of competent larvae with no increase in rearing volumes.     

肾上腺素对岩牡蛎幼虫变态的诱导

为了得到壳型规则、大小均一的单体牡蛎,本研究采用肾上腺素对岩牡蛎单体苗种生产的诱导条件进行研究,阐明了岩牡蛎单体苗种的最适诱导浓度、诱导时间和诱导密度。结果显示,肾上腺素能显著诱导岩牡蛎幼虫的不固着变态,最适诱导浓度为5×10–5 mol/L,最适诱导时间为1 h,提高诱导浓度和延长诱导时间导致岩牡蛎幼虫的不固着变态率、稚贝壳高和存活率显著降低;肾上腺素对低于8个/mL幼虫密度的诱导效果差异不显著,但稚贝壳高和存活率在8个/mL的培育密度下显著低于0.5～4个/mL,研究表明利用肾上腺素诱导岩牡蛎单体时,可大批量处理眼点幼虫,但稚贝充气培养的最适培养密度应不高于4个/mL。     

斑节对虾Chitinase-2基因的克隆及其在蜕皮和幼体发育过程中的表达分析

研究以斑节对虾(Penaeus monodon)转录组获得的几丁质酶基因(Pm Chi)片段,运用RACE技术克隆了PmChi基因c DNA全长,命名为PmChi-2。PmChi-2基因c DNA全长2 050 bp,其中5'-非编码区(5'-UTR)144 bp、3'-UTR 319 bp和开放阅读框(ORF)1 587 bp,编码528个氨基酸。生物信息学分析显示,PmChi-2与其他甲壳动物Chi-2的相似性为78%~97%。实时荧光定量PCR结果显示,PmChi-2在蜕皮前期(D期)表皮中表达水平最高,在胃、鳃、腹神经节和眼柄中表达水平依次降低,在其他组织(肝胰腺、肠、肌肉、心脏)中几乎不表达。不同蜕皮阶段,PmChi-2在鳃、胃和表皮3种组织中的表达变化模式基本一致,均在蜕皮期(E期)表达量最低,而最高表达量在鳃中出现在蜕皮后期(A期),在胃和表皮中为D期。幼体不同发育阶段分析揭示PmChi-2 mRNA在幼体发育阶段的无节幼体到糠虾幼体第二期表达量维持在一个低水平,在糠虾幼体第三期PmChi-2 mRNA表达水平显著升高,在仔虾期又显著下降,推测PmChi-2 mRNA可能与斑节对虾幼体发育密切相关。研究结果表明PmChi-2基因可能在斑节对虾蜕皮以及幼体的变态发育中发挥重要作用,为深入研究斑节对虾几丁质酶发育调控提供了重要信息。     

New ways and new hopes for IGR development

Insect Growth Regulators (IGRs) represent advanced, bio-rational insecticides. This Special Issue reflects progress in IGR development that has been enabled by insight into the molecular principles of biosynthetic or hormone signaling pathways. The unifying principle is aiming at processes and molecular targets that are unique to arthropods and ideally to narrower insect taxa representing pests or disease vectors. While some strategies of obtaining the desired compounds for chemical intervention rely on rational, structure-based design or computational power, others exploit technologies allowing automated, high-throughput screening of large chemical libraries. All avenues leading to selective and environmentally safe pest control are valid as we face the imminent threat of the declining world insect population.     

Effect of different ions on larval metamorphosis of the mussel Mytilus galloprovincialis

Metamorphic responses of pediveliger larvae of Mytilus galloprovincialis to different ions were investigated through a series of bioassays. Effects of tetraethylammonium chloride (TEA) on inductive effects of these above ions were also investigated. Excess ions including Li⁺, Cs⁺, Rb⁺ and Ca²⁺ induced larval metamorphosis at 10^?3 M to 5 × 10^?2 M in 24‐h exposure assays. In continuous exposure assays, only excess Ca²⁺ showed inductive activity and induced 25% metamorphosis at 5 × 10^?2 M. Larval responses to Li⁺ and Rb⁺were inhibited by TEA, while induction of metamorphosis by Cs⁺and Ca²⁺ was independent of the presence of TEA. Thus, these ions used can be useful inducers of larval metamorphosis for application in the aquaculture industry. The finding provides new insights on the biochemical mechanism controlling larval metamorphosis in this species.     

褐牙鲆早期发育阶段CRH基因表达及受甲状腺激素的影响

【目的】探析褐牙鲆仔鱼早期发育阶段促肾上腺皮质激素释放激素基因(CRH)的表达情况及受甲状腺激素的影响作用,为开展牙鲆的人工繁育提供科学依据。【方法】通过实时荧光定量PCR检测褐牙鲆早期发育阶段CRH基因表达量,以ELISA测定褐牙鲆仔鱼甲状腺激素(T3和T4)水平,并测定经外源T3浸泡处理后早期发育褐牙鲆仔鱼CRH基因表达量的变化情况,探究CRH和甲状腺激素在褐牙鲆早期发育阶段的影响及作用关系。【结果】1~8日龄褐牙鲆仔鱼CRH基因相对表达量呈先升高后降低的变化趋势,在5日龄达最高值,显著高于其他日龄的仔鱼(P0.05,下同)。10~42日龄褐牙鲆仔鱼CRH基因主要在其头部表达,尾部CRH基因的相对表达量随着生长发育的进程而逐渐增加。褐牙鲆仔鱼变态前期甲状腺激素T4含量逐渐增加,变态高峰期迅速升高,在变态后期呈下降趋势。较其他早期发育时期,甲状腺激素T3在褐牙鲆变态期维持高水平,但含量低于甲状腺激素T4。22日龄褐牙鲆仔鱼经50 nmol/L外源T3处理2 h后,其头部和尾部CRH基因的相对表达量显著升高;但以外源T3处理8 h后,无论是头部还是尾部,CRH基因的相对表达量均呈显著下降趋势。【结论】褐牙鲆早期变态发育需CRH基因高表达及甲状腺激素积累,二者对褐牙鲆早期变态发育阶段具有重要作用并呈互相代偿效应。     

Morphological development and allometric growth of yellowtail kingfish Seriola lalandi V. larvae under culture conditions

Morphological development and allometric growth patterns of Seriola lalandi larvae were assessed to characterize normal growth patterns under culture conditions. Early ontogenetic stages of yellowtail kingfish exhibited an exponential growth in terms of standard length as a function of age. Five development stages were characterized from hatching to the juvenile stage: larval stage I (0–2 days post hatch, dph) with endogenous feeding, characterized by a small yolk sac, unpigmented eyes, primordial finfold surrounding the body and a closed mouth; larval stage II (2–15 dph) characterized by mouth opening, complete pigmentation of eyes and the beginning of the exogenous feeding; subsequently, in the larval stage III (15–25 dph) the posterior tip of notochord of the larvae bended upward and the first rays appeared in fins, concomitant with a change in swimming behaviour; thereafter, larval stage IV (post‐flexion stage; 25–30 dph) began when larvae resembled in morphology to a juvenile organism; however, caudal and dorsal fins were not completely development. Lastly, the juvenile stage was reached 30 dph characterized by a morphology and fin structures similar to those of the adults. Growth and development of structures and organs associated with vital functions such as feeding, sensorial and breathing systems seemed to be more critical previous to 23 dph, which was reflected with a positive allometric growth of head and eyes during this period. The results from this study can be used as a tool‐guide to assess normal development in larval research with S. lalandi to improve existing rearing protocols in hatchery production.     

Low salinity increases survival,body weight and development in tadpoles of the Chinese edible frog Hoplobatrachus rugulosus

Water salinity affects survival, growth and metamorphosis of anuran tadpoles. Hoplobatrachus rugulosus is considered not only as a freshwater amphibian but is also found in brackish wetlands. However, whether salinity change interferes with hatching, survival, body mass and development of H. rugulosus tadpoles is unknown. We found that salinity levels of <4‰ did not affect of survival or hatching of H. rugulosus eggs. At an early larval stage, tadpoles could tolerate up to 9‰ salinity for 96 h; however, body water content decreased when salinity was >5‰. After a 3‐week experiment, body weights of tadpoles exposed to 2‰ and 4‰ salinities were higher but that of the 6‰ group was lower compared with the 0‰ group. More than 90% of tadpoles exposed to 2‰ and 4‰ salinity showed complete metamorphosis. Salinity levels <4‰ promoted survival of tadpoles better than 0‰, whereas none of tadpoles in the 6‰ group became juvenile frogs in 50 days. Time taken to reach metamorphosis was shorter for 2‰ and 4‰ (47.22 ± 0.28 and 47.26 ± 0.33 days, respectively) than for 0‰ (49.31 ± 0.35 days). Juvenile frogs in the 2‰ group had greater body weight than the control. It could be concluded that salinity of <4‰ increased survival and body weight of H. rugulosus tadpoles, and shortened the time taken to reach metamorphosis.