Does the wild‐caught Chinese mitten crab megalopae perform better than the hatchery‐produced seed during the juvenile culture?

Although wild Yangtze Eriocheir sinensis juveniles (coin‐sized seed) have better culture performance than the pond‐reared juveniles during the adult crab culture stage, the culture performance of wild‐caught megalopae (WC) remains unknown. Therefore, this study was designed to compare the growth, survival rate, crab yield, feed conversion rate (FCR), precocity, final weight and size distribution between WC and hatchery‐produced megalopae (HP) during the juvenile culture stage. Wild‐caught megalopae had significantly higher body weight, weight gain rate (WGR) and specific growth rate (SGR) during 0–4 weeks but lower WGR and SGR than HP during 4–8 weeks (p < .05). Although WC had a significantly lower survival rate and yield of normal juvenile crabs than HP, total yields of normal juveniles and precocious crabs were similar. Wild‐caught megalopae had a significantly higher precocious rate and yield of precocious crabs than HP (p < .05). Regardless of sex, no significant differences were found in the gonadosomatic index (GSI), hepatosomatic index (HSI) and final weight of normal juveniles and precocious crabs between WC and HP. As for the size distribution of normal crabs, WC had a higher percentage of small female juveniles (<3 g) but a lower proportion of middle size ranges (3–5.99 g and 6–8.99 g) than HP for females (p < .05), and there was no significant difference for males. In conclusion, wild megalopae of the Yangtze E. sinensis had worse culture performance than the hatchery‐produced seeds; therefore, wild megalopae would not be recommended for commercially juvenile culture of E. sinensis.     

Can genetic diversity be maintained during mass selection of the Chinese mitten crab,Eriocheir sinensis?

The Chinese mitten crab (Eriocheir sinensis) is an important aquaculture species and food source in Eastern Asia. This study assesses the changes in genetic diversity in successive generations of early‐ and late‐maturing strains of E. sinensis using 30 microsatellite markers with high polymorphism. The mean average number of alleles (N) in the founder population (G0), first generation (G1), second generation (G2) and third generation (G3) of the early‐maturing strain were 18.367, 14.800, 16.400 and 16.533, respectively; while in late‐maturing strain the values were 18.500, 16.267, 14.367 and 16.533 respectively. Likewise, there was a slight decline in average allelic richness (R_s) in the three successive generations. In both strains, the mean observed heterozygosity (H_o) remained relatively constant for the early‐maturing strain and the values were 0.655, 0.667, 0.685 and 0.705, respectively; and for the late‐maturing strain these were 0.665, 0.672, 0.688 and 0.702 respectively. Similarly, the expected heterozygosity (H_e) remained constant, ranging from 0.823 to 0.854. There was a decrease in effective population sizes (N_e) of the early‐maturing strain with successive generations: values were 492.2, 35.0, 134.7 and 193.2, respectively; while the values in the late‐maturing strain were 1268.5, 75.6, 111.5 and 97.2 respectively. All pairwise population distances were very close in both strains. In conclusion, these results suggest that mass selection of E. sinensis did not significantly diminish genetic diversity although there was a decline for the N_e. Therefore, it is important to maintain sufficient broodstock numbers and a large effective population when following a selective breeding programme.     

Biochemical and Microbiological Assessment of Crucifix Crab (Charybdis feriatus) Stored at 4°C

Charybdis feriatus is a highly prized crab in the local and international markets of East Asian countries. In local markets, crabs are sold live, iced, or refrigerated at 2°C – 4°C. The present study was carried out to determine the shelf life of whole crab stored at 4°C for 192 h using a set of biochemical, microbiological, and sensorial parameters. Biochemical indicators such as the total volatile base nitrogen (TVB-N) and trimethylamine nitrogen (TMA-N) increased significantly during storage and within an acceptable limit up to 144 h. Regarding the biogenic amines, cadaverine and spermidine increased significantly (p < 0.05) during the storage period. Among them, cadaverine could be proposed as a useful spoilage indicator for this crab species. The mesophilic and psychotropic bacterial count exceeded the limit of acceptance after 144 h of storage. Sensory attributes were gradually diminished with the storage time. Sensory scores were found to correlate well with both mesophiles and psychrotrophs. Based on the results of this study, the meat quality of Charybdis feriatus can be maintained up to 144 h when properly stored at a temperature of 4°C ± 1°C.     

Effects of different dietary vitamin E and astaxanthin levels on growth,fatty acid composition and coloration of the juvenile swimming crab,Portunus trituberculatus

Six isonitrogenous and isolipidic diets were formulated containing two astaxanthin (AX; 0 and 90 mg/kg) and three vitamin E (VE) levels (0, 25 and 50 mg/kg). There were three replicates (18 crabs per replicate) for each treatment. Juvenile swimming crab (initial weight 31.65 ± 0.06 g/crab) were fed different diets for 8 weeks. After the feeding trial, growth performance was not significantly affected by the different treatments. Crabs fed with AX‐supplemented diets showed more redness. Whole body 22:6n‐3, 22:4n‐6 and 20:5n‐3 levels increased with the dietary addition of AX (P = .009, P = .002 and p = .042, respectively). The malondialdehyde (MDA) concentrations of fresh/frozen hepatopancreas and frozen muscle were significantly decreased by the dietary AX supplementation (p < .001, p = .010 and p = 0.011, respectively). These findings provide evidence that dietary AX has an ability to improve the redness of the shell and reduce the MDA concentrations of tissues. Furthermore, there is no strong interactive relationship between dietary VE and AX on the coloration and fatty acid concentrations for the swimming crab.     

Quality assessment of newly hatched mud crab,Scylla serrata,larvae

Starvation and exposure to formalin were investigated as possible stress tests for evaluating the quality of mud crab, Scylla serrata, larvae. For the starvation stress test, newly hatched zoeae stocked in 150‐ml containers were either starved or fed rotifers. Similarly, newly hatched zoeae were stocked in containers with seawater of 0 (control), 20, 30 and 40 mg/L formalin for the formalin stress test. The zoeae from the same batches were used for seed production to monitor their performance and validate the results of stress tests. Starvation was found to be unsuitable for larval quality evaluation. However, the impact of initial food deprivation on the newly hatched larvae indicates that feeding immediately after hatching is necessary for mud crab larvae. Exposure of larvae to 40 mg/L formalin for 3 hr appeared to be a reliable and practical method for larval quality assessment as the survival of larvae in the mass production tanks validated the classification of good and poor quality batches in the stress tests. On this basis, a hatchery operator can decide which batch should be cultured further. Finally, there appears to be a link between the quality of larvae and the performance at the megalopa and early juvenile crabs.     

光色对中华绒螯蟹幼体诱集与仔蟹摄食的影响

为揭示不同发育阶段中华绒螯蟹Eriocheir sinensis对光照颜色的行为反应,探究蟹类颜色视觉的特征,采用自制的试验装置,研究了蓝光(波长446~493 nm)、绿光(波长502~579 nm)、黄光(波长586~600 nm)、红光(波长620~644 nm)、白光(波长440~637 nm)对中华绒螯蟹Ⅱ~Ⅴ期溞状幼体与大眼幼体的诱集效果,以及对仔蟹摄食的影响。结果表明:在室内试验装置中,Ⅱ~Ⅴ期溞状幼体和大眼幼体在蓝光下的分布率最高,极显著高于其他光照组(P0.01),各期幼体在绿光下的分布率也不同程度地高于其他光照组;在室外土池中,采用容积为1 L的捕苗器,在蓝光下捕获大眼幼体的数量最多,为1097尾,极显著高于白光组(253尾)、红光组(121尾)和黄光组(35尾)(P0.01),显著高于绿光组(629尾)(P0.05);24 h内各光色组中仔蟹的昼夜摄食量结果显示,各组仔蟹的日摄食量无显著性差异(P0.05),白天摄食量平均值高于夜晚,但差异并不显著(P0.05)。     

不同移栽方式对烤烟‘KRK26’生长发育和产质量影响研究

为研究不同移栽方式对烤烟‘KRK26’生长发育和产、质量影响,进行了膜下小苗移栽与膜上壮苗移栽对比试验。结果表明,膜下小苗移栽方式能有效促进烤烟生长发育,缩短烤烟大田生育期,烟叶成熟期提前8天。同时改善烟叶外观质量,化学成分更加协调,使烟叶单产提高10.5%,上等烟率提高0.9%,产值提高11.3%。试验证明了德宏烟区膜下小苗移栽的优势,为德宏烟区烤烟最佳移栽方式提供依据。     

Stepwise function of natural growth for Scylla serrata in East Africa: a valuable tool for assessing growth of mud crabs in aquaculture

Predicting growth is critical in aquaculture, but models of growth are largely missing for mud crab species. Here, we present the first model of natural growth in juvenile and adult mud crabs Scylla serrata from East Africa using a stepwise growth function based on data on intermoult periods and growth at moult from field mark‐recapture, pond and laboratory studies. The results showed a sigmoid growth pattern in carapace width and suggest that S. serrata in East Africa will reach 300 g and sexual maturity ~9.9 months after settlement, and a commercial size of 500 g after 12.4 months. Analyses of the literature identified several issues with the common praxis to compare standard growth measures between aquaculture studies with different initial size or growing periods. Using the new growth function to estimate the proportional difference between modelled and obtained growth as an alternative method, we show that growth rates of S. serrata cultured in cage systems, which are dominant in East Africa, was <40% of the estimated natural growth and growth obtained in pond systems. The analysis also indicated that growth rates of S. serrata in Southeast Asia was over 50% higher compared with similar culture systems in East Africa, and that different species of mud crabs had large differences in growth rates. This study shows that growth in the present mud crab aquaculture systems in East Africa is below their expected potential. Further work is needed to identify the factors behind this observation.     

淡水虾蟹养殖池塘中5种水草的营养成分比较

比较虾蟹池塘中微齿眼子菜、线叶眼子菜、菹草、空心莲子草和穗花狐尾藻5种水草的常规营养成分、总类胡萝卜素、脂肪酸和氨基酸含量,并结合5种水草的生长特性和对底泥再悬浮的抑制作用,综合评估这5种水草在淡水虾蟹养殖中的应用价值.试验结果显示:(1)菹草水分含量显著高于其他4种水草,微齿眼子菜、线叶眼子菜和空心莲子草的粗蛋白和粗...     

PMSG诱导荷斯坦青年母牛发情试验研究

[目的]为了诱导始配年龄的部分青年母牛发情,提高奶牛的繁殖效益.[方法]对20头荷斯坦青年奶牛应用孕马血清PMSG注射用绒促性腺素进行诱导发情处理.[结果]处理后1～9 d内出现发情的有18头,发情率为90%,未发情率为10%;5头对照牛发情率为10%,未发情率为90%(P<0.01).[结论]PMSG处理诱导青年母牛发情的效果显著、确实、可靠.