利用500Hz方波连续音驯化南海真鲷幼鱼的效果

在实验室条件下采用500 Hz方波连续音对体长范围为4.4～6.6 cm的南海真鲷（Chrysophrys major）幼鱼连续进行8 d音响驯化研究,试验数据利用Origin软件的Gaussion模型分析。结果显示,对照组试验鱼在水池中随机分布,试验组试验鱼在驯化第1天至第8天出现频次最大的区域分别距离水池中心点105.40 cm、93.51 cm、88.04 cm、83.40 cm、71.86 cm、83.06 cm、83.23 cm和96.85 cm。试验组反应时间从第5天起缩短趋势已无明显变化,一直处于最短状态,驯化第2天开始低于对照组;聚集时间第4天起缩短趋势变化不明显,一直处于最短状态,驯化全过程低于对照组;停留时间第5天起增加趋势变化不明显,均处于最长时间,驯化全过程高于对照组;聚集率在第4天起达到最佳,驯化全过程高于对照组。由此可见,500 Hz方波连续音对真鲷幼鱼具有良好的驯化效果,并且在驯化5 d后即可建立良好的条件反射。     

Juvenile hormone III, hydroprene and a juvenogen as soldier caste differentiation regulators in three Reticulitermes species: potential of juvenile hormone analogues in termite control

The efficacy of juvenile hormone III (JH III) and two JH-mimicking compounds was compared in laboratory experiments with Reticulitermes lucifugus (Rossi), R. santonensis Feytaud and R. virginicus (Banks). Induction of presoldier, soldier and/or soldier-worker intercaste differentiation was taken as positive response to the treatment. The novel juvenogen, a fatty acid ester of a juvenoid alcohol, induced greatest soldier differentiation in all species tested, followed by hydroprene. JH III was less effective. Representatives of three Reticulitermes species showed similar trends in soldier induction rates. Differences in mortality in treatments of termites of the same species from different colonies with the same compound were observed and evidently were caused by differences in the conditions of respective colonies.     

Stocking Density for Nursery Production of Redclaw Crayfish,Cherax quadricarinatus,in a Recirculating System

Redclaw crayfish, Cherax quadricarinatus, early juveniles were reared at different stocking densities in a closed recirculation system using 12-L plastic containers as rearing tanks. Initial stocking densities were 1.0, 1.5, 2.0, 2.5, and 3.0 per liter (66, 89, 111, 133, and 156 crayfish/m², respectively). Rearing period was 42 days. Each density was tested with five replicates. Shelter (0.112 m²) was added to double the surface area of rearing tanks. Animals were fed ad libitum twice a day with a commercial diet containing 35% crude protein. There were no significant differences (P < 0.05) in length and specific growth rate (SGR) among stocking densities. Final weight and daily weight gain, however, were significantly higher at the density of 66 per m² (1.0 per liter). Total biomass at harvest increased with density. Survival was affected by stocking density from day 28 onward, decreasing with density from 62.7 ± 7.6% obtained at 66 crayfish/m² to 44.85 ± 8.18% at 156 crayfish/m².     

Optimum Dietary Level of Chlorella Powder as a Feed Additive for Growth Performance of Juvenile Olive Flounder,Paralichthys olivaceus

ABSTRACT

The present study was conducted toestimate the optimum dietary supplementation level of Chlorella powder as a feed additive to optimize growth of juvenile olive flounder, Paralichthys olivaceus. Four experimental diets supplemented with Chlorella powder (CHP) at 0, 1, 2 and 4% (CHP₀, CHP₁, CHP₂, and CHP₄, respectively) of diet as a dry-matter (DM) basis were prepared. Three replicate groups of fish averaging 1.1±0.02 g were fed one of the four experimental diets for 12 weeks. After the feeding trial, fish fed the CHP₂ diet had a higher (P < 0.05) weight gain (819%) than did fish fed CHP₀ (707%) and CHP₁(712%); however, there was no significant difference between fish fed CHP₂ (8197%) and CHP₄ (7559%) as among fish fed CHP₀, CHP₁, and CHP₄ (P > 0.05). Fish fed CHP₂ had a higher (P < 0.05) feed efficiency (134%) than did fish fed CHP₀ (123%); however, there was no significant difference (P > 0.05) among fish fed CHP₀ (123%), CHP₁ (125%), and CHP₄ (125%) as among fish fed CHP1 (125%), CHP₂ (134%), and CHP₄ (125%). Fish fed CHP₂ and CHP₄ had a lower (P < 0.05) serum glucose level (average 32.9 mg/dL) than did fish fed CHP₀ and CHP1 (average 34.8 mg/dL). Fish fed CHP1 and CHP₂ had a lower (P < 0.05) serum glutamic oxaloacetic transaminase (GOT) level than did fish fed CHP0 and CHP₄. Glutamic pyruvic transaminase (GPT) levels significantly (P < 0.05) deceased as dietary CHP increased. Fish fed CHP₂ and CHP₄ had a less (P < 0.05) whole-body fat than did fish fed CHP₀. These results indicate that the optimum dietary supplementation level of Chlorella powder as a feed additive in juvenile olive flounder could be approximately 2% of diet.     

Interannual variation in pelagic juvenile rockfish (Sebastes spp.) abundance – going with the flow

We report results from 28 yr of a midwater trawl survey of pelagic juvenile rockfish (Sebastes spp.) conducted off the central California coast. The fishery‐independent survey is designed to provide pre‐recruit indices of abundance for use in groundfish stock assessments. Standardized catch rate time series for 10 species were developed from delta‐generalized linear models that include main effects for year, station, and calendar date. Results show that interannual fluctuations of all 10 species are strongly coherent but highly variable, demonstrating both high‐ and low‐frequency components. A similarly coherent result is observed in the size composition of fish, with large fish associated with elevated catch rates. In contrast, spatial and seasonal patterns of abundance show greater species‐specific differences. A comparison of the shared common trend in pelagic juvenile rockfish abundance, derived from principal components analysis, with recruitments from five rockfish stock assessments shows that the time series are significantly correlated. An examination of oceanographic factors associated with year‐to‐year variability indicates that a signature of upwelled water at the time of the survey is only weakly related to abundance. Likewise, basin‐scale indices (the Multivariate El Niño‐Southern Oscillation Index, the Pacific Decadal Oscillation, the North Pacific Gyre Oscillation, and the Northern Oscillation Index) are poorly correlated with abundance. In contrast, sea level anomalies in the months preceding the survey are well correlated with reproductive success. In particular, equatorward anomalies in the alongshore flow field following the spawning season are associated with elevated survival and poleward anomalies with poor survival.     

The effect of dietary n‐3 series fatty acids on the number of pleopadal egg and stage 1 juvenile in freshwater crayfish,Astacus leptodactylus Eschscholtz

The effect of dietary n‐3 series fatty acids on the number of pleopadal egg and stage 1 juvenile in freshwater crayfish, Astacus leptodactylus was investigated. Crayfish were fed with n‐3 series fatty acids supplemented diets and a control diet for 251 days. Control diet did not comprise additional n‐3 series fatty acids. However, D2, D3 and D4 groups were supplemented with n‐3 series fatty acids at 1%, 2% and 3% level respectively. Results showed the beneficial effects of dietary n‐3 series fatty acids on the production of pleopodal egg and stage 1 juvenile number. At the end of the experiment, pleopodal egg (from 177 to 234) and stage 1 juvenile number (from 167 to 225) increased significantly with increased dietary n‐3 series fatty acid level. In addition, an increase in dietary n‐3 series fatty acids led to an increase in number of pleopodal egg and stage 1 juvenile produced per gram of female crayfish weight. It can be concluded that the reproductive efficiency of A. leptodactylus (i.e., pleopodal egg and stage 1 juvenile number) can be improved in controlled hatchery conditions by adding n‐3 series fatty acid into the diet of this species.     

Prey–predator dynamics in seahorses (Hippocampus guttulatus): deciphering fatty acid clues

Understanding the flow of fatty acids between trophic levels can provide important clues on prey–predator dynamics and nutritional requirements of the species. This study investigates the fatty acid flow between enrichment emulsions, Artemia nauplii and Hippocampus guttulatus juveniles, and evaluates the nutritional value of enriched and unenriched Artemia for newborn seahorses. The fatty acid profile of Artemia and seahorses generally reflected the dietary composition, but fatty acids were not linearly transferred between trophic levels. The incorporation of dietary fatty acids showed to be a more complex process involving dietary composition, predator metabolism and nutritional requirements. Artemia composition resulted from a dynamic balance between what was assimilated and metabolized by the nauplii during enrichment. Prey fatty acids were incorporated in seahorses, but HUFA, particularly DHA, were selectively retained to fulfil their high requirements. H. guttulatus newborns were not successfully reared on Artemia nauplii, not even on enriched Artemia, with low survival rates (15.0–26.7%) being observed in all feeding treatments. The high MUFA content and low DHA level of Artemia did not fulfil the high SFA and PUFA requirements of newborn juveniles, particularly their great DHA demands. Higher survivorship was obtained with enriched Artemia, but no differences were detected in juvenile growth.     

美洲西鲱仔鱼不可逆点及仔、稚鱼摄食特性研究

在水温(20.5±1.0)℃的条件下,采用实验生态学的方法,对美洲西鲱(Alosa sapidissima)仔鱼在饥饿状态下的生长、形态、不可逆点(PNR)及仔、稚鱼期的摄食节律进行了研究,旨在阐明美洲西鲱早期发育过程中的摄食规律和特点。实验结果表明,美洲西鲱初孵仔鱼全长(7.45±0.15)mm,体质量为(2.15±0.03)mg,卵黄囊体积为(5.99±0.13)mm3,第5日龄,仔鱼卵黄囊被完全吸收。对照组仔鱼全长及体质量随着卵黄囊的消耗、外源性营养的建立逐渐增加;饥饿组仔鱼自6日龄开始,全长及体质量开始呈现负增长,至10日龄全部死亡。美洲西鲱初孵仔鱼初次摄食时间在3日龄,摄食率为46.67%,5日龄摄食率达到最大为89.29%,PNR发生在7~8日龄,综上所述,美洲西鲱仔鱼最佳投喂时间应在2~3日龄。美洲西鲱仔、稚鱼摄食节律研究表明,美洲西鲱早期仔鱼(4日龄)昼夜摄食高峰出现在14:00,平均摄食量达到0.14 mg;晚期仔鱼(17日龄)在10:00和14:00出现较高的摄食量,分别为0.92和1.36 mg;28日龄稚鱼在10:00、14:00和18:00 3个时间段维持着较高的摄食量,摄食量分别为1.77、2.45和1.55 mg,属于典型的白天摄食类型,且随着仔稚鱼的生长发育,摄食高峰期逐渐延长。美洲西鲱仔、稚鱼各阶段的日摄食率分别为20.08%(4日龄)、29.48%(17日龄)和12.41%(28日龄),可将其作为美洲西鲱日投喂量的参考标准。     

Evaluation of transportation methods of juveniles of the Australasian sea cucumber,Australostichopus mollis

The transport of juvenile sea cucumbers to grow‐out sites is problematic as they are prone to damage and mortality. The response of juvenile Australostichopus mollis to simulated transport conditions with and without seawater for different periods of time (2, 4, 8, 12 and 24 h) at different temperatures was evaluated in this study. Sea cucumbers were placed in plastic bags with seawater or wrapped in a seawater‐soaked cloth. Monitoring of evisceration, skin lesions, feeding activity and survival was used to evaluate the success of transportation. The juveniles of this species can withstand being without seawater for up to 8 h with no consequences to their survival and feeding activity. Complete immersion of the juveniles in seawater was found to be the only option for transportation over longer periods, but preventive measures should be taken to avoid detrimental levels of temperature, oxygen and pH. Overall, the existing constraints to moving juvenile sea cucumbers to grow‐out sites can be overcome through preventing desiccation during short‐term transport without seawater, and by the control of temperature for long‐term transportation with seawater. The results suggest that in juvenile sea cucumbers, feeding activity and the presence of skin lesions are more sensitive indicators of the success of transport than evisceration and survival.     

The food limitation hypothesis for juvenile marine fish

Coastal zones are productive areas that serve as nursery grounds for a large number of marine species. However, the processes involved in survival success during the juvenile phase are not well‐known. Some authors suggest that the availability of prey is important to support the production of pre‐recruit fish whose fitness is enhanced through optimal feeding conditions. Accordingly, recruitment is limited by the carrying capacity of the nursery habitat. In contrast, other authors state that the carrying capacity of the nursery grounds is not fully exploited, suggesting that there is no effect of food limitation. This study combines an overview of the literature, focused on flatfish that are especially dependent on coastal and estuarine nursery grounds, an extension to other marine fishes and a modelling approach on growth and survival of juvenile fish to explore the controversy of food limitation in their nursery grounds. We demonstrate that the relative lack of growth limitation observed for young marine fishes at the individual scale is related to an observational bias: fish have been affected by size‐selective mortality linked to food limitation, but only surviving individuals are observed. As the population is skewed towards the faster‐growing juveniles, the growth of survivors remains close to optimal, even when food resources are limited. Food limitation is of major influence in determining the carrying capacity of the nursery habitat. To sustain marine fish populations and related fisheries, management action is needed to protect coastal and estuarine areas and maintain or restore nursery productivity.