Simulation of mackerel (Scomber scombrus) recruitment with an individual-based model and comparison with field data

An individual‐based model (IBM) for the simulation of year‐to‐year survival during the early life‐history stages of the north‐east Atlantic stock of mackerel (Scomber scombrus) was developed within the EU funded Shelf‐Edge Advection, Mortality and Recruitment (SEAMAR) programme. The IBM included transport, growth and survival and was used to track the passive movement of mackerel eggs, larvae and post‐larvae and determine their distribution and abundance after approximately 2 months of drift. One of the main outputs from the IBM, namely distributions and numbers of surviving post‐larvae, are compared with field data as recruit (age‐0/age‐1 juveniles) distribution and abundance for the years 1998, 1999 and 2000. The juvenile distributions show more inter‐annual and spatial variability than the modelled distributions of survivors; this may be due to the restriction of using the same initial egg distribution for all 3 yr of simulation. The IBM simulations indicate two main recruitment areas for the north‐east Atlantic stock of mackerel, these being Porcupine Bank and the south‐eastern Bay of Biscay. These areas correspond to areas of high juvenile catches, although the juveniles generally have a more widespread distribution than the model simulations. The best agreement between modelled data and field data for distribution (juveniles and model survivors) is for the year 1998. The juvenile catches in different representative nursery areas are totalled to give a field abundance index (FAI). This index is compared with a model survivor index (MSI) which is calculated from the total of survivors for the whole spawning season. The MSI compares favourably with the FAI for 1998 and 1999 but not for 2000; in this year, juvenile catches dropped sharply compared with the previous years but there was no equivalent drop in modelled survivors.     

Lipid enrichment for Senegalese sole (Solea senegalensis) larvae: effect on larval growth, survival and fatty acid profile

Results from three larval Senegalese sole (Solea senegalensis) feeding trials using non-enriched Artemia and Artemia enriched with Super HUFA®, Arasco®, sunflower oil and microalgae are presented and the effects on larval survival, growth and fatty acid (FA) composition are reported. The FA profile of Senegalese sole eggs was analysed to gather information about the nutritional requirements of the early larval stages and a quite high DHA/EPA ratio (4.3) was found. However, there was no evidence of a high dietary demand for DHA or EPA, given that no relationship was found between dietary HUFA concentration and larval growth and survival. When larvae were fed non-enriched Artemia a significantly better growth and comparable survival were obtained than with Artemia enriched with Super HUFA® (containing the highest HUFA level and DHA/EPA ratio). The FA profiles of the larvae generally reflected those of their diets. DHA was an exception, as it was present in high proportions, even in larvae fed DHA-deficient prey. Total FAME concentration decreased during larval development, with SFA, MUFA and PUFA being equally consumed; HUFA appeared to be less used, with its relative concentration being either kept constant (particularly EPA and ARA) or increased (DHA). A specific requirement for ARA in the first larval stages could not be confirmed but it was always present in considerable amounts, even in larvae fed an ARA poor diet.     

对虾传染性皮下及造血组织坏死病毒(IHHNV)的流行病学与检测技术研究进展

对虾传染性皮下及造血组织坏死病(IHHN)是国际兽疫局(OIE)划定的甲壳类其他重要疾病之一，它分布广泛，危害严重，对世界对虾养殖业的发展影响重大。随着国际贸易的不断发展，区域间个体的流动有可能造成该病病毒传播。有迹象表明，近几年来中国养殖对虾中已发现IHHNV，且呈流行趋势。目前，国际上已建立起多种标准检测方法以监控疾病的流行。本文就该病毒的病毒特性、感染宿主、传播途径、地理分布及诊断技术等方面的研究现状作一综述，旨为对虾病毒性流行病学调查及疾病监控提供参考。     

卵形鲳鲹的早期胚胎发育

对人工繁殖的卵形鲳鳆（Trachinotus ovatus）受精卵的胚胎发育过程进行了连续观察。受精卵由人工养殖的性成熟亲鱼，经人工催产、自然产卵受精获得。卵形鲳鲮的成熟卵呈圆形，平均卵径为967．8μm。受精卵在水温18～21℃、盐度31的条件下，胚胎发育历时41h27min后孵出仔鱼。胚胎发育为盘状卵裂，胚体后期的发育速度较快；仔鱼脱膜孵化的速度非常快，基本上在1min内就可以完成。初孵仔鱼平均全长为1．548mm，卵黄囊较大。     

Supplementation of ascorbic acid 2-monophosphate during the early postlarval stages of the shrimp Penaeus vannamei

A culture trial was performed using five levels of ascorbic acid 2-monophosphate (AmP at 0, 10, 100, 1000 and 2000 mg kg⁻¹ diet, expressed as active ascorbic acid, AA) in a semipurified diet for early postlarval Penaeus vannamei. The experiment started 10 days after metamorphosis of the mysid larvae into postlarvae (=PL10). Each treatment was run in four replicates. P. vannamei postlarvae showed significantly better growth according to dietary AA level after 25 days of feeding, i.e. at PL36 stage. Whereas the dry weight of PL36 in the control treatment (0 mg AA kg⁻¹ diet) was only 2 mg, supplementation of 1000 mg AA kg⁻¹ increased the shrimp dry weight up to 18 mg. However, the growth in the other treatments was not significantly different from the control. Fitting a broken-line regression to the biomass yield demonstrated an optimal dietary level of 130 mg AA kg⁻¹ diet. There were no differences observed among the treatments in stress resistance of postlarval P. vannamei to a salinity shock.     

Weaning of Atlantic halibut Hippoglossus hippoglossus L. using formulated diets with various levels of ascorbic acid

Atlantic halibut larvae (120 mg) were weaned to formulated diets with different supplementations of ascorbate- poly-phosphate, ApP (300, 2000 and 3000 mg ascorbic acid (AA) equivalents kg⁻¹ diet). The experiment lasted for 50 days with cofeeding of enriched Artemia and formulated diets during the first 30 days. During the last 20 days, only formulated diets were offered to the fish. One control group was fed only Artemia (770 mg AA kg⁻¹ dry weight) during the entire experimental period. The specific growth rate during the 50 days was ≈ 4.5% day⁻¹ and the mean weights in all dietary groups were ≈ 1 g when the experiment was terminated. No differences in mean weight and mortality were observed between the groups fed formulated diets and that fed Artemia during the experiment. The fish size in the groups fed formulated diets ranged between 0.10 and 3.05 g and this differed from the Artemia group where the size ranged between 0.35 and 1.35 g. Dietary levels of ApP had no positive effect on growth and survival. The retention of AA was significantly higher in the groups fed high dietary levels of ApP. Apparently, the bioavailability of high dietary levels of ApP appeared to be low for young halibut. After stressing the fish using a high-salinity challenge test, no significant difference in survival occurred among the dietary groups. Cortisol levels in plasma recorded 3 h post stress was significant lower in the Artemia group compared with the groups fed the formulated diets.     

Rates of Yolk Utilization and Effects of Delayed Initial Feeding in the Larvae of the Freshwater Fishes Rohu and Singhi

The yolk utilization rates and effects of delayed initial feeding were examined on the feeding ability, survival and growth of the larvae of two freshwater species, rohu, Labeo rohita and singhi, Heteropneustes fossilis reared in the laboratory at 26 (2) °C. Although the yolk reserves in both species lasted at least 7 days after hatching, all larvae initiated feeding by the fifth day, indicating a short period of mixed (endogenous and exogenous) feeding. When first feeding was delayed beyond the fifth day, subsequent weight gains and survival rates declined progressively for both rohu and singhi, although their feeding abilities were not adversely affected until the seventh (singhi) and eleventh (rohu) day. The point of no return (PNR) (when 50% of the unfed larvae were unable to feed when offered food) was reached in singhi when they were 8 days old and in rohu when they were 14 days old. Even among the larvae that fed at PNR, their subsequent mortality rate was nearly 100%, reflecting the irreversible effects of starvation. This study showed that rohu were more resistant to starvation than singhi.     

大泷六线鱼仔鱼摄食及生长的研究↑（*）

本文以大泷六线鱼(Hexagrammosotakii)人工孵化所得的卵黄囊期仔鱼为材料,对仔鱼早期阶段的摄食及生长情况作了实验研究。结果表明:在13.5～14℃条件下,大泷六线鱼仔鱼6日龄开始摄食,约8日龄卵黄囊耗尽,10日龄饥饿仔鱼进入PNR期,混合营养期为2d;饥饿仔鱼的开口率(初次摄食率)开始较低,此后上升,到卵黄囊耗尽时达高峰(63%),以后又下降。仔鱼前期的生长率平均为0.254mm/d,饥饿仔鱼生长几乎停止,同期喂食仔鱼的生长率亦下降为0.102mm/d;摄食仔鱼在孵化后20d内的全长(L)和日龄(d)的相关式为L=0.085d 7.04。仔鱼存在昼夜摄食节律,在1昼夜中有2个摄食高峰,分别出现在14:00和20:00。     

Effect of arachidonic acid supplementation on reproductive performance of tank‐domesticated Penaeus monodon

The reproductive performance of domesticated Penaeus monodon was assessed when fed on two experimental semi‐moist maturation diets varying in their arachidonic acid content for 21 days before ablation and throughout a 17‐day reproductive assessment. The biochemical composition of the two semi‐moist two diets was similar with the exception of arachidonic acid (ARA) content; the basal diet (BAS) consisting of 0.9 g kg^?1 DM ARA (1.1% of total fatty acids) and the supplemented diet (ARA‐SUP) consisting of 5.0 g kg^?1 DM ARA (5.8% of total fatty acids). ARA/EPA and ARA/DPA ratios were 0.1 in the BAS diet and 0.5 in the ARA‐SUP diet. Fatty acid composition of the spawned eggs was comparable between diets with the exception of ARA concentration, which was higher in the ARA‐SUP (8.95 ± 0.44 g kg^?1 DM) than the BAS (3.23 ± 0.17 g kg^?1 DM) (P < 0.0001). The cumulative percentage of females spawning (mean ± SE after 17 days) (31.9 ± 7.0%; 24.1 ± 1.3%), number of spawnings per female (0.48 ± 0.1; 0.29 ± 0.02), and eggs per female (62 520 ± 16 935; 44 521 ± 9914) was significantly (P < 0.0001) higher for the ARA‐SUP than the BAS. Results of this study suggest that arachidonic acid plays a key role in promoting egg development and spawning in P. monodon.