Characterization of microsatellite loci from the Japanese eel Anguilla japonica

The Japenese eel, Anguilla japonica, is generally assumed to be composed of a single population with wide distribution range, and some genetic studies using allozyme or mitochondrial DNA methods supported this population model. However, one genetic study suggested the existence of multiple populations in this species, and thus, more detailed studies on the population structure is needed. Here we characterized a total of 11 microsatellite markers of the Japanese eel. These will serve as powerful tools for detailed population study for the Japanese eel, though two of them showed the significant departure from the Hardy–Weinberg expectations.     

据于矢耳石Sr/Ca值的长江日本鳗鲡迁移格局多样性分析(英文)

长江口是中国日本鳗鳗苗的主要产区和仅存的成鳗渔业水域。日本鳗自长江河口至上游金沙江近3000km干流及许多支流中都有分布,但其迁移行为却不为人了解。该文分析了2008年9～11月采自长江靖江段(31o30′N,120o42′E)的153尾银色鳗样本的生物学特征,测定了其中27尾标本的矢耳石Sr/Ca值。结果显示,153尾样本中有雌性85尾、雄性68尾,雌雄性比1:0.8。雌性由3～7(平均5.52)龄组成,平均体长(669±80)mm,体重(555±229)g,丰满度1.77±0.22,性腺指数(GSI)1.32±0.31。雄性由3～5(平均4.38)龄组成,平均体长(518±51)mm,体重(234±76)g,丰满度1.62±0.18,GSI0.21±0.11。雌性的这些生物学参数均显著大于雄性(P<0.05)。依据矢耳石线鳗标志轮平均Sr/Ca值(7.99±1.05)×10-3进行判断,有17尾(即62.96%个体)为"淡水型",10尾(即37.04%个体)为"河口型"。16尾雌性中有13尾(即81.25%)为"淡水型",3尾为"河口型"。11尾雄性中仅36.36%为"淡水型",63.64%为"河口型"。对每个生长层组的Sr/Ca值分析表明,雌雄间2龄时无显著差异,但3龄、4龄和洄游龄组都有显著或极显著的差异,预示着2龄时两者的栖息水域比较一致,但后来出现了明显栖息地分化。     

Internal illuminance and shelter shape affect shelter selection by the Japanese eel Anguilla japonica

The present study evaluated the effects of internal illuminance and shelter shape on shelter selection by Japanese eels to enable the preservation or construction of suitable shelters for the Japanese eel. Japanese eels were able to distinguish a 1.25-fold difference in illumination inside the shelters, and preferred darker shelters. When the internal illumination of two shelters with the same shape was less than one-tenth of the ambient illumination (about 400 lx), shelter selection by Japanese eels was not affected by internal illuminance, even when there was a 10-fold difference in internal illumination between shelters. The width of the shelter was not important, but Japanese eels preferred a deep shelter with a low ceiling and walls that spread to a ‘dead end’. This has important implications on the creation of suitable shelters for Japanese eels.     

Temperature effects on the incorporation of strontium in otolith of Japanese eel Anguilla japonica

The effects of temperature on somatic and otolith growth and the incorporation of strontium in otolith of the Japanese eel, were studied in laboratory-reared and field-caught eels. The somatic and otolith growth rates of the eel increased significantly with temperature and were estimated as approximately 0·096 mm t.l, (P<0·01) and 0·36 μm in otolith diameter per degree-day (0·01相似文献   

Recruitment mechanism of the eel, Anguilla japonica, to the Japanese coast

A total of 149 Anguilla japonica elvers collected at 10 locations along the Japanese coast were aged according to otolith daily increments. The interrelationships among age, birth date, body size, pigmentation stage, sampling location and the timing of recruitment were examined in order to determine the recruitment mechanism of elvers to coastal waters.
First catches of eels were earlier in the locations at lower latitudes. Age at recruitment was roughly constant, 218 ± 29 (mean ± s.d.) days old, disregarding the localities, but a weak positive correlation was obtained between age and sampling date or timing of recruitment. Body length at recruitment was also constant, 56.3 ± 2.3 mm s.l., and showed no significant correlation with either locality or recruitment timing. Estimated birth date ranged from April to November, the mean ± s.d. being 22 July 1982 ± 42 days, suggesting a peak season spawning in summer. Birth date was closely related with both the latitude of location and sampling time. Pigmentation developed more at lower latitude. Recruitment mechanism of the Japanese eel was summarized as follows: the earlier-born individual recruits earlier at lower latitude and at younger age, but at a constant body size.     

Unravelling the life-history patterns and habitat preferences of the Japanese eel (Anguilla japonica) in the Pearl River,China

Eels have fascinated biologists for centuries due to their amazing long-distance migrations between freshwater habitats and very distant ocean spawning areas. The migratory life histories of the Japanese eel, Anguilla japonica, in the waters of south China are not very clear despite its ecological importance, and the need for fishery regulation and management. In this study, strontium (Sr) and calcium (Ca) microchemical profiles of the otoliths of silver eels were measured by X-ray electron probe microanalysis based on data collected from different habitats (including freshwater and brackish habitats), in the large subtropical Pearl River. The corresponding habitat preference characteristics were further analysed using redundancy analysis (RDA). A total of 195 Japanese eels were collected over 6 years. The collected individuals ranged from 180 to 771 mm in total length and from 8 to 612 g in body weight. Two-dimensional pictures of the Sr:Ca concentrations in otoliths revealed that the A. japonica in the Pearl River are almost entirely river eels, spending the majority of their lives in fresh water without exposure to salt water, while the catadromous migration time has delayed about 1 month in the Pearl River estuary in the past 20 years. RDA analysis further indicated that juveniles and adults preferred water with high salinity and high tide levels. Youth preferred habitats with high river fractals. Our findings contribute to a growing body of evidence showing that the eels are extremely scarce currently and conservation measures against them are imminent, including the protection of brackish and freshwater areas where they live in south China.     

Changes in otolith microchemistry of the Japanese eel, Anguitta japonica, during its migration from the ocean to the rivers of Taiwan

The newly recruited Japanese eel, Anguilla japonica , elvers and 1-year-old eels collected in estuaries and in rivers, respectively, were studied. The microstructure and chemical composition of the sagittal otolith of these eels were examined by SEM and wavelength-dispersive spectrometer (WDS), A transition zone or'elver mark'was observed in the otolith of the young eels. A comparison of the otoliths of elvers with those from the 1-year-old eels suggests that this transition zone was deposited during upstream migration, a change from a marine to freshwater environment. Strontium (Sr) content in the primordium of the otolith of both elvers and young eels was low, probably due to the maternal or freshwater origin of the oocyte. The concentration of Sr in the otolith increased gradually during marine life and reached a peak approximately 1 month before upstream migration. As the elvers entered the estuary, the Src concentration dramatically decreased and remained at a low level thereafter. These findings indicate that the history of the migratory environment of the eel can be reconstructed from a combined study of otolith microstructure and microchemistry analysis.     

Opsonic effect of antiserum and complement on phagocytosis by macrophages from the peritoneal cavity of the Japanese eel, Anguilla japonica

Macrophage exudates in the Japanese eel, Anguillu japonica, were induced by intraperitoneal injection with a mixture of Edwnrdsiella bacterin, proteose peptone and liquid paraffin, and the opsonic effect of antiserum and complement on the phagocytic activity of the macrophages was studied.
The macrophages contained a round nucleus with a nucleolus, and an agranular cytoplasm with projecting processes. These cells showed phagocytosis of sheep red blood cells (SRBC). An opsonic effect of antiserum was recognized in terms of a significant increase of macrophage phagocytic activity against SRBC treated with antiserum relative to that against SRBC treated with inactivated normal serum. Complement, however, did not enhance the phagocytic activity of macrophages.     

The distribution, density and growth of the European eel, Anguilla anguilla, in the freshwater catchment of the River Thames

Improvements in water quality in the Thames Estuary since the 1960s have removed a barrier to fish migration into the Thames catchment. The extent of recolonization by the eel is examined, using data from 235 electrofished and fyke-netted sites, compared with information on pre-pollution distribution. Density is highest in the lower parts of the catchment and decreases significantly with increasing distance from the tidal limit. Only sparse populations are found beyond 50 km from the tidal limit and are characterized by an increasing bias towards larger, slower-growing females. Artificial stocking is believed to be a significant factor in certain areas. The rate of recolonization has been slow and neither the annual natural recruitment nor distribution of the pre-pollution stock of the 1800s appears to have been achieved. The future management of the stock in relation to its commercial scientific and conservation value is considered.     

Temperature influence on the spawning performance of artificially-matured Japanese eel, Anguilla japonica, in captivity

We studied the influence of temperature on the spawning performance of artificially matured Japanese eels, Anguilla japonica, in captivity. We used routine hormone injections to bring females and males to maturity in separate aquaria. We recorded the behavior of three pairs of such hormone-treated matured eels in an aquarium (2 replicates) at four temperatures: 14, 18, 22, and 27°C, respectively. They became active and frequently left the bottom swimming in the water column, and spawning events occurred. Females released eggs in the water column around the activity peaks. Males preceded females in reaching activity peaks (presumably the timing of sperm ejection and egg release), possibly resulting in the low fertilization we observed in this experiment. Males and females returned back to the aquarium bottoms and became quiet after spawning. On several occasions, male-female or female-female pairs were observed to ‘cruise together’ in the water column for several to tens of seconds prior to egg releasing, but no courtship behavior indicative of spawning such as pairing and chasing was observed in the eels in our study. Our results suggest that 18–22°C might be the thermal preference for spawning for Japanese eels, which approximates the temperature range of the 500 m deep water layer around the Mariana Islands seamount area, the presumed spawning site for the Japanese eel.

Location,size and age at onset of metamorphosis in the Japanese eel Anguilla japonica

This study clarifies the location, size and age at the onset of metamorphosis in Japanese eels Anguilla japonica through oceanic surveys, rearing experiments and analyses of the morphology and otoliths of leptocephali and glass eels. Twenty‐eight metamorphosing leptocephali were collected in the mesoscale eddy region to the east of Taiwan during research expeditions in 2004. Rearing experiments showed that the total length (L_T) of leptocephali decreased by an average of 12·5% during metamorphosis and 13·9% during the 2–12 h after death. Thus, the mean back‐calculated L_T at the onset of metamorphosis for 630 glass eels from Taiwan and Japan was estimated at 67·8 ± 2·7 mm (mean ± S.D.). The estimated mean ante‐mortem size of the fully grown pre‐metamorphic leptocephali collected in 2004 was 64·6 ± 3·4 mm, which was consistent with the L_T estimate for glass eels. Otolith analysis showed that the mean age at the onset of metamorphosis was 137 ± 15 days and indicated that Japanese eels may have a recruitment route through the mesoscale eddies to the east of Taiwan in addition to the direct transfer route from the North Equatorial Current to the Kuroshio Current.     

Variation in the sex ratio, size and age of longfinned eels within and among coastal catchments of south‐eastern Australia

Longfinned eels Anguilla reinhardtii were captured by both fishery‐dependent and independent sampling methods from three rivers in New South Wales, south‐eastern Australia. Sex ratios, catch per unit effort and population age and total length structure were examined in three zones (fresh water and upper and lower tidal) in the Hacking, Hawkesbury and Clarence Rivers. Females were found in relatively high proportions in all zones, ranging from 97% in a freshwater (non‐tidal) site down to 59% in a tidal site. Males were found primarily in tidal zones (only two of the 677 longfinned eels caught in non‐tidal fresh water were males), with the greatest proportions being found in the brackish upper tidal areas. The mean number of fish captured per trap was higher in the fresh water and upper tidal zones than in the lower tidal zones. The mean ±  s . e . age, 17·9 ± 0·3 years, and age range, 5–52 years for females were significantly higher than those of males 12·2 ± 0·4 years; range 5–22 years, which is typical of other anguillid species. Longfinned eels captured in fresh water were found be significantly larger and older than those in tidal zones due to the almost exclusive predominance of females.     

Factors determining length distribution and abundance of the European eel, Anguilla anguilla, in the River Mondego (Portugal)

1. The distribution and abundance of the European eel, Anguilla anguilla, were investigated in the Mondego River, a strongly modified river in central Portugal. Nine freshwater sites, located below the first impassable obstacle to eel migration, were surveyed for 2 years. The study was conducted monthly during the first year and seasonally during the second year. Fish were caught by electric fishing and, physical and biotic variables potentially influencing eel length distribution and abundance were determined at each sampling session. 2. Canonical correspondence analysis (CCA) was used to explain the relationships between abiotic and biotic habitat variables, and eel length distribution. Spatial variation was strongly associated with distance from the sea, number of obstacles, river width and percentage of instream cover. Depth, river flow, water temperature and cannibalism had weaker effects on the longitudinal distribution, but contributed as explanatory variables for the model. The influence of spatial variables outweighed the importance of temporal variables as predictors in this model. 3. Length distribution changed in space from a dominance of small eels (<100 mm) closer to the sea to larger eels (≥250 mm) in the upper reaches of the river. The smallest length class (eels <100 mm) was strongly associated with wider stretches where instream cover, mainly composed of aquatic submerged macrophytes, was abundant (>75% area coverage). On the contrary, larger eels (≥250 mm) preferred deeper stretches with stronger river flow and less instream cover. 4. The effect of biotic interactions with conspecifics as well as with the non‐native red swamp crayfish Procambarus clarkii, in sites with poor instream cover, modified this general pattern of distribution leading to fewer eels <100 mm at some sites closer to the sea. Therefore, despite the ubiquity and plasticity shown by this species, there were clear ontogenetic variations in habitat use such that the first two canonical axes of a CCA accounted for 58.4% of the spatial variability in size structure.     

Cloning, Sequencing, and Phylogenetic Analysis of Complementary DNA of Novel Cytochrome P-450 CYP1A in Japanese Eel (Anguilla japonica)

Complementary DNA of cytochrome P-450 CYP1A, in addition to CYP1A1, has been isolated from Japanese eel (Anguilla japonica) liver treated with 3-methylcholanthrene. The cDNA contained a 5′ untranslated region of 66 bp, an open reading frame of 1554 bp coding for 517 amino acids and a stop codon, and a 3′ untranslated region of 1166 bp. The predicted molecular weight of the Japanese eel CYP1A was approximately 58.5 kDa. The nucleotide sequence exhibited identities with the reported CYP1A1 sequences of 77% for Japanese eel, 75% for rainbow trout, 72% for scup, plaice, and butterfly fish, and 71% for toadfish. The deduced amino acid sequence exhibited identities with the reported CYP1A1 sequences of 78% for Japanese eel, 77% for rainbow trout, 75% for scup, 74% for toadfish, 73% for plaice, and 72% for butterfly fish. The novel eel CYP1A obtained had less similarity to the other teleost CYP1A1 proteins (72%–78%) than that of the eel CYP1A1 (74%–80%). When compared with mammalian CYP proteins, the novel eel CYP1A was more similar to the CYP1A1 proteins (54%–56%) than to the CYP1A2 proteins (50%–53%). The phylogenetic tree of the teleost CYP1A genes constructed using the maximum likelihood method suggested that the novel eel CYP1A is ubiquitous among the Anguilliformes. Received August 25, 2000; accepted November 30, 2000     

Purification and characterization of a novel imidazole dipeptide synthase from the muscle of the Japanese eel Anguilla japonica

We have purified a novel enzyme from eel white muscle which catalyzes the syntheses of imidazole dipeptides, such as carnosine (β-alanyl-l-histidine), anserine (β-alanyl-π-methyl-l-histidine), and balenine (ophidine; β-alanyl-τ-methyl-l-histidine), directly from their precursors. The enzyme was purified 1130-fold from eel muscle by a series of column chromatographies. Although eel muscle contains a large amount of carnosine and only trace amounts of anserine and balenine, the anserine synthesizing activity was by far the highest. From gel permeation chromatography, the molecular mass of the enzyme was calculated to be 275 kDa. SDS-PAGE of the purified enzyme represented a band around 43 kDa, suggesting that the native enzyme is a hexamer or heptamer. The optimal pH and temperature were around 9.5 and 60 °C, respectively. K_m values for β-alanine and π-methyl-l-histidine were 44 and 89 mM, respectively. The enzyme was greatly activated by Zn²⁺ and inhibited by EDTA. The N-terminal amino acid sequence of 25 residues of the purified enzyme showed 52% amino acid identity to 38–62 residues of zebrafish haptoglobin precursor. The purified enzyme also exhibited hydrolytic activity against these imidazole dipeptides.     

长江口日本鳗鲡幼体色素发育时相及其体型变化

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Intraseasonal characterization of glass eel migration in the River Tiber: space and time dynamics

Glass eel ( Anguilla anguilla ) upstream migration was studied in the River Tiber estuary to obtain a better understanding of spatial and temporal migration dynamics within the season of ascent. Using data from glass eel fisheries, time series analysis of daily catches per unit of effort revealed a fortnightly cycle that can be related to invasion waves possibly corresponding to tidal currents. The amplitude of these waves appeared to correspond to the tidal area of the estuary. Furthermore, glass eels apparently had a delay in this area before resuming upstream migration.     

Differential effects of origin and salinity rearing conditions on growth of glass eels of the American eel Anguilla rostrata: implications for stocking programmes

In this study, growth patterns were monitored in controlled fresh and brackish water (BW) conditions for 7 months during Anguilla rostrata glass eel and elver stages. Null hypotheses tested were that there is no significant difference in growth between glass eels (1) collected from two geographic regions typified by different sex ratios, (2) reared in fresh and BW and (3) due to origin × salinity interactions. It was found that young A. rostrata from Mira River (MR, Cape Breton, Nova Scotia, Canada, an area where both males and females occur) grew faster than those from Grande-Rivière-Blanche (Québec, Canada, an area where population are highly skewed towards females; 99–100%). Anguilla rostrata from both origins also grew faster in BW, although there was a trend for origin × salinity interactions whereby this effect was more pronounced for fish from the MR. The results support the hypothesis that salinity can influence growth patterns, as possibly can quantitative genetic differences between A. rostrata glass eels from different origins. Possible explanations for these patterns and potential consequences for sex determination and translocation programmes are discussed.     

Populations of Bothriocephalus claviceps (Goeze) (Cestoda) in the European eel, Anguilla anguilla (L.), in three localities in southwest England

The population biology of Bothriocephalus claviceps (Goeze) has been investigated in the European eel, Anguilla anguilla (L.), in three localities in southwest England. Monthly changes in prevalence and abundance show no statistically significant seasonality, in contrast to growth and reproduction of the cestode. The cestode reaches maximum size and becomes gravid mainly in summer. Gravid cestodes die and are lost soon after reproduction. This overlaps with recruitment of the new generation into eels, and may result in a rapid increase in infection levels and in a more over-dispersed distribution of the parasite in some localities, or in a more gradual change in infection levels and over-dispersion in others. Development and growth of the new generation may cease until the following spring, or continue at a slow rate over winter. Parasite numbers in each host decrease well before they actually reach maturity, since the majority of gravid individuals are present in those eels which harbour only one parasite. This suggests that few cestodes develop to maturity and most are lost from hosts as development proceeds.     

Variation in Population and Life History Traits of the American Eel, Anguilla rostrata, in Four Rivers in Maine

We examined population traits of yellow American eels from nine sites with similar habitat characteristics in each of four rivers in Maine, U.S.A. Migrating silver eels were also collected to compare sex ratio, age and size at migration among the four rivers. Population density and biomass were not significantly different among rivers with mean ranges of 8.4–21.8 eels 100m^–2and 380–1485gm^–2. Pairwise comparisons of the slopes of weight–length relationships of log transformed data (pooled data: intercept = –6.007, slope = 3.094, r²= 0.99, and n = 3116) revealed no significant differences among rivers. Length–age relationships (pooled data: intercept = 87.826, slope = 23.444, r²= 0.76, and n = 2325) also showed no statistically significant pairwise differences in slopes among rivers. In all rivers, sexual differentiation was complete by 270mm total length and age eleven. The sex ratios of migrating silver eels were not correlated with yellow eel sex ratios among the four rivers. Mean age at migration among the four rivers was significantly different for males only, with a range of 1.3years. Both sexes had some significant differences in size at migration among rivers, but the biological importance of the differences is tenuous (male range: 15mm, female range: 36mm). The yellow and silver eel population traits from these four rivers showed little variation when riverine habitat was isolated. Variations in traits appeared to be greater when eels from non-riverine habitats may have been present.