Antibody production in Japanese eels, Anguilla japonica Temminck & Schlegel

Adult Japanese eels, Anguilla japonica Temminck & Schlegel, (200–250 g, 45–55 cm) were immunized by intramuscular injection with goat IgG. After 5 weeks, eel immunoglobulin (Ig) was purified using affinity chromatography. The purified eel Ig was used to immunize rabbits to produce anti-eel Ig antibody. The highest antibody ELISA value in eels was reached 3 weeks after initial immunization with goat IgG, and then gradually decreased. The antibody could still be detected at 140 days post-immunization. The optimal temperature for antibody production was 30°C. Freund's complete adjuvant and secondary immunization both increased antibody production in eels.     

Genetic variability of the Japanese eel Anguilla japonica (Temminck & Schlegel) related to latitude

Abstract— Isozyme genotypes of 400 glass eels recruiting to 4 localities along the east Asian coast, stretching from Taiwan to the Yalu River of northeastern China, were studied using starch gel electrophoresis. Geographic cline was found to exist in two loci: NADP-isocitrate dehygenase-1 and 6-phosphogluconate dehydrogenase. Frequencies of the most common allele of these two loci increased from south to north. In the latitudinal range of 25°N to 40°N, the magnitude of difference of IDH100 and PGD100 was 13% and 9% respectively. However, deviations from Hardy-Weinberg equilibrium were found to be insignificant in both loci at three of the four localities. The cline was, therefore, unlikely to have resulted from selection. Migration time-lag from different parts of the continent to the spawning ground in the western Pacific was suggested to be a possible reason for the formation of the cline.     

Demonstration of infectious pancreatic necrosis virus strain VR-299 in Japanese eel, Anguilla japonica Temminck & Schlegel

Abstract. Six isolates of infectious pancreatic necrosis virus (IPNV) were obtained from trout or eel farms in Taiwan in 1987. By using the electrophoretic analysis of ³⁵S-methionine-labelled early viral polypeptide patterns and silver-stained ds RNA gel patterns, a comparison of these isolates with the three archetypal IPNV serotypes (AB, SP and VR-299) was made. They were all identical with VR-299, both in the RNA and early viral polypeptide patterns. From the results obtained, it was apparent that the VR-299 serotype of IPNV was just as widespread in eel as in trout in Taiwan. This is the first case of VR-299 isolation from eel.     

Humoral immune response of Japanese eel, Anguilla japonica Temminck & Schlegel, to Pleistophora anguillarum Hoshina, 1951 (Microspora)

A humoral response of Japanese eel, Anguilla japonica Temminck & Schlegel, to the microsporean Pleistophora anguillarum Hoshina was demonstrated using immunoblotting and an enzyme-linked immunosorbent assay (ELISA). Japanese eel immunoglobulin was purified by affinity chromatography. The immunoglobulin was composed of 25-kDa light chains and 72-kDa heavy chains. The ELISA values of P. anguillarum antibodies in naturally infected fish sera were significantly higher than those of clinically healthy fish. Spore proteins from the microsporean were separated by electrophoresis and subjected to analysis by Western blot. Sera from naturally infected fish showed different reaction patterns to the spore proteins. While the sera randomly selected from naturally infected eels all showed a significant positive reaction to P. anguillarum antigens, the mucus from only three out of the nine infected eels reacted positively in the ELISA test. Subsequent analyses indicated that there was no significant difference in the amount of mucus immunoglobulin among the tested eels. Therefore, the generally lower ELISA values of mucosal anti-P. anguillarum antibodies from the infected eels tested were evidently not caused by a lack of immunoglobulin per se, but seem to be the result of a lack of anti-P. anguillarum antibodies in the mucus and/or a lower affinity in the anti-P. anguillarum antibodies that were present.     

Cell-mediated immunity of the eel, Anguilla japonica (Temminck & Schlegel), as measured by the migration inhibition test

Abstract. Sensitized lymphocytes isolated from the immunized eel, Anguilla japonica , upon interaction with the antigens in vitro , elaborated into the medium a soluble factor which was capable of inhibiting the migration of peritoneal exudate cells harvested from guinea pigs. Production of migration inhibition factor (MIF) was greatest to the specific antigen although there was also some nonspecific release. The elaboration of MIF from the sensitized lymphocytes occurred from the third day after immunization of eels and was detectable until day 106. The inhibitory activity from the blood appeared to persist over a longer period compared to that from the spleen and the anterior kidney. The inhibitory activity, however, was diminished by starvation of the immunized eels.     

Gill filament necrosis in farmed Japanese eels, Anguilla japonica (Temminck & Schlegel), infected with Herpesvirus anguillae

A herpesviral gill disease accompanied by mass mortality occurred in Japanese eels, Anguilla japonica (Temminck & Schlegel), reared in warm water ponds from 1993 to 1995. Diseased fish displayed marked haemorrhage and congestion within gill filaments and destruction at the tips of affected filaments with necrosis and inflammation in the central connective tissue and the central sinus. Electron microscopy revealed herpesvirus particles in infected fibrocytes within the filamental connective tissue. The isolate was identified as Herpesvirus anguillae by a neutralization test. Infectivity experiments with the isolates revealed that the virus was pathogenic.     

Haemoglobin powder as a dietary fish meal replacer in juvenile Japanese eel, Anguilla japonica (Temminck et Schlegel)

Two consecutive 6-week feeding trials were conducted to determine the amount of haemoglobin powder (BM) that could replace fish meal (FM) in juvenile Japanese eel Anguilla japonica (Temminck et Schlegel) diets. Fish were fed 50% crude protein diets in which each of ten isonitrogenous diets was formulated to contain white fish meal and/or blood meal as the dietary protein source to replace FM by BM as follows: Diet 1 (control), 0% BM; diet 2,12.5% BM; diet 3,25% BM; diet 4, 50% BM; diet 5, 75% BM; diet6,100%BM;diet7,25%BM + 3 Essential Amino Acids (EAA); diet 8, 50% BM + 3 EAA; diet 9, 75% BM + 3 EAA; diet 10, 100 BM + 3 EAA. In the first 6-week period, the results were not consistent with the treatments, and poor adaptation of the fish to the experimental diets and conditions was observed. In the second 6-week period, weight gain, specific growth rate, protein efficiency ratio and protein productive value offish fed diets 2, 3, 4, 7, 8 and 9 were not significantly different from those of fish fed the control diet (P > 0.05). However, feed conversion ratios offish fed diets 6 and 10 were lower than that offish fed the control diet (P < 0.05). These results demonstrate that FM can be replaced by BM up to 50% without supplementation of three EAA, and up to 75% with three EAA supplementation in juvenile Japanese eel diets.     

Hen egg yolk and skinned krill as possible foods for rearing leptocephalus larvae of Anguilla japonica Temminck & Schlegel

Usual diets for rearing leptocephalus larvae of Japanese eel Anguilla japonica include eggs of the endangered spiny dogfish Squalus acanthias (SE). We investigated the effects of alternative food materials, hen egg yolk (HEY) and exoskeleton‐free (skinned) Antarctic krill (SAK), on the growth and survival of eel larvae. We found that feed comprising whole krill including exoskeleton (WAK) containing higher levels of fluoride (37.89 mg kg^?1) was acutely toxic to eel larvae exposed to this alone. In contrast, extract from SAK containing lower concentrations of fluoride (4.25 mg kg^?1) showed no apparent adverse effects. Growth of larvae fed a mixture of SE and SAK in a feed trial of 58 days [mean body weight (BW), 6.0 mg] was about twofold higher than that of larvae fed a mixture of SE and WAK (3.2 mg) (P < 0.01). A mixture of HEY and SAK also had some dietary benefits for eel larvae, enabling them to survive for up to 58 days and to grow significantly (mean BW, 2.4 mg), compared with their initial weight (mean BW, 0.2 mg) (P < 0.001). Although additional nutritional improvements are needed, the present results suggest that combination diet HEY and SAK may be a good alternative to SE as an effective diet for eel larvae.     

Maturational factors as indicators of egg quality in Japanese eel, Anguilla japonica

In order to identify maturational factors that can serve as indicators of egg quality in artificially matured Japanese eel, Anguilla japonica, maturation-promoting factor (MPF; consists of cdc2 and cyclin B) related proteins and chromosomes were examined. Mitogen-activated protein kinase (MAPK; 44 kDa band) and cdc2 (35 kDa and 34 kDa band) were detected. Chromosomes aligned on a vertical spindle appeared normal; however, chromosomes on a horizontal spindle and dispersed chromosomes seemed unusual.     

Biochemical composition of eggsin relation to egg quality in the Japanese eel, Anguilla japonica

This paper presents the relationship between egg quality and egg biochemical composition of cultured and wild Japanese eel, Anguilla japonica. Eggs were obtained by artificialinduction of maturation. Fertilization and hatching rates were used as characteristics of egg quality. Egg quality characteristics showed large variation; fertilization rate, 0–96; hatching rate, 0–84%. The biochemical composition also showed a large variation. There was no marked relationship between egg quality and fatty acid contents of eggs, except for n-6 highly unsaturated fatty acids (HUFA). Both the fertilization and hatching ratesincreased proportionally withincreases of the -tocopherol g(-Toc) contentin eggs. A more significant correlation was found between the amount of -Toc relative to the amount of HUFA and egg quality. The results of this study show that the egg quality of Japanese eel is affected by the –Toc level, andin particular, the ratio of -Toc to HUFAin the eggs. Abbreviations: BHT – butylhydroxytoluene; EFA – essential fatty acids; FAME – fatty acid methyl esters; HPLC – high performance liquid chromatography; HUFA – highly unsaturated fatty acids; NADH – nicotinamide adenine dinucleotide; NADPH - nicotinamide adenine dinucleotide phosphate; ROS – reactive oxygen species; -Toc –-tocopherol.     

日本鳗鲡产卵后生存及其繁育

为证明日本鳗鲡(Anguilla japonica)生活史最后一步一产后鳗的命运,本研究模拟产后的日本鳗鲡继续在海水中养殖,观察其存活率及繁育情况.结果表明,产后鳗在海水中停食约18 d后,体能得到恢复,部分亲鱼开始出现摄食,1个月左右全部恢复摄食,经244 d养殖,雌、雄鳗体质量增加,存活率达94.6%.随后,给产后鳗注射外源性促性腺激素(鲤鱼脑垂体匀浆CPE和人绒毛膜促性腺激素HCG)后激发其退化的性腺(卵巢和精巢)重新发育(与当年银鳗作对照).通过性腺组织切片观察产后鳗和对照鳗性腺发育成熟的全过程及其差异,发现产后鳗起初性腺发育比当年银鳗差,但经多次注射激素后,产后鳗性腺成熟与当年银鳗同步,证明产后鳗生殖细胞对激素的敏感件高.应用17α,20β-双羟孕酮和促性腺激素释放激素类似物(GnRH-A3)使催熟的产后鳗和对照鳗均产卵和排精,并孵化出仔鱼,从而有力地证明,鳗鲡产后虽体质弱,但待体能恢复后能够继续生存和繁殖.本研究旨在探讨利用产后鳗作为今后鳗鲡人工繁殖亲鳗的可行性.     

日本鳗鲡人工繁育研究的进展

从日本鳗鲡亲本的选择、人工催熟催产技术、仔鳗的饵料开发、仔鳗的培育装置及培育方法等方面综述了目前在日本鳗鲡繁育方面的最新研究成果,以期为国内日本鳗鲡的人工繁殖研究提供参考资料.     

日本鳗鲡排卵的人工诱导

对日本鳗鲡(Anguillajaponica)卵巢发育的时间与催产率的关系进行研究,对卵母细胞在体内胚泡破裂(GVBD)的发生过程、以及用17α-OHP和17α,20β-DHP诱导日本鳗鲡排卵的方式、时机和催产效果进行观察,结果表明,卵巢发育时间越长,催产率越低。造成催产率低的原因主要是由于日本鳗鲡在卵母细胞成熟后期,雌鳗个体对催产药物敏感性差异较大,催产时机难以掌握。通过采用适合日本鳗鲡卵母细胞的透明液观察GVBD的发生过程,并根据每个个体GVBD的发生速度,制订适宜的催产方案基本解决了上述难题。本实验采用CP、HCG、17α-OHP或17α,20β-DHP混合催产,使其平均催产率由35 4%分别提高到91 9%和93 0%。17α-OHP和17α,20β-DHP的催产剂量为5mg/(500g)和10mg/(500g)。在(21±0 5)℃水温条件下,催产效应时间分别为15～18h和13～16h。     

Demographic survey of the yellow-phase Japanese eel Anguilla japonica in Japan

Catch statistics and biological data of the Japanese eel Anguilla japonica from 12 river systems in nine prefectures of Japan (36°N, 140°E–31°N, 130°E) during 1999–2004 were analyzed in order to evaluate the demography of A. japonica in Japan. Significant differences in biological characteristics of 6388 eels were found among the river systems. Fishery catches of eels in all locations have declined, but the magnitudes or patterns of decline seem to be different. Of sex-identified eels, mean total lengths ± SD (mm) of females (n = 3776) and males (n = 962) were 495.6 ± 104.3 and 412.9 ± 80.7, respectively, and overall sex ratio (% female) was 79.6 %. Mean age (years) and growth rate (mm year^?1) were 5.0 ± 1.9 and 96.7 ± 38.6 for females (n = 3643) and 3.6 ± 1.7 and 120.5 ± 65.4 for males (n = 907), respectively. This study highlights the demographic heterogeneity of the A. japonica among the studied river systems, which suggests that it is important to conserve a variety of habitats in multiple river systems as an inclusive management target in addition to restoration of the diversity of habitats for eels in a single river system.     

Artificial induction of maturation and fertilization in the Japanese eel, Anguilla japonica

Repeated injections of salmon pituitary extract (20 mg per fish per week) induced vitellogenesis in feminized, cultivated Japanese eels (Anguilla japonica). Oocytes were attained at the migratory nucleus stage after 11 or 12 injections. Addition of 17,20-dihydroxy-4-pregnen-3-one (DHP) into the incubation medium induced germinal vesicle breakdown (GVBD) in the oocytes at the migratory nucleus stage. An injection of DHP (2 µg g^-1 BW), given 24h after an injection of salmon pituitary extract (20 mg fish^-1), succeeded in inducing maturation and ovulation in females which contained occytes at the migratory nucleus stage. Most fish ovulated 15–18h following the DHP injection. Eggs that were ovulated within 15h after the DHP injection showed high fertility and hatchability, but eggs ovulated 18 or 21h after the DHP injection, showed considerably lower fertility and hatchability. A delay between ovulation and stripping of the eggs rapidly decreased both the fertility and hatchability within 6–9h after ovulation, indicating that artificial fertilization must be carried out immediately after ovulation. Repeated injections of human chorionic gonadotropin (hCG) at a concentration of 1 IU g^-1 BW week^-1 induced spermatogenesis, spermiation, and the acquisition of potential for sperm motility in cultivated males. Most males spermiated after the fifth or sixth injection of hCG, and the milt weight gradually increased and remained constant (1–2 g) from the 11th to 31th injection. Sperm motility peaked 24h after each weekly injection, and decreased from the 3^rd day after the injection. Potassium ions are an essential constituent for the maintenance of motility in the eel spermatozoa. Artificial seminal plasma containing 15.2 mM KCl is applicable as a milt diluent. Using these techniques developed for female and male eels, we have succeeded in obtaining many fertilized eggs from cultivated eels.