Advanced sexual maturation before marine migration of Anguilla bicolor bicolor and Anguilla marmorata at Réunion Island

Maturing sub-adults of two species of anguillid eels (a female Anguilla bicolor bicolor and a male Anguilla marmorata ) were collected for the first time at Réunion Island, western Indian Ocean. Both were silver eels, i.e. maturing eels at the onset of their spawning migration, and characterized by advanced sexual maturation that has been only observed in Anguilla dieffenbachii from New Zealand.     

Age and growth of Anguilla bicolor bicolor leptocephali in the eastern Indian Ocean

A sampling survey for leptocephali was conducted in the eastern Indian Ocean to the west of Sumatra from 5 to 20 June 2003 in an overlapping area with the historical survey in September to November 1929 during the Danish Round the World Expedition. The age and larval growth rate of 34 Anguilla bicolor bicolor collected in 2003 were estimated using their otolith microstructure to obtain new information about the early life history of this sub-species. The total lengths and ages of these leptocephali were 44·1–55·5 mm and 114–158 days, respectively. Their hatching dates ranged from 3 January to 20 February 2003. Combining these age data and the estimated age of leptocephali collected by others in the same area, this sub-species was estimated to have a wide range of spawning periods. Individual growth rates of the leptocephali in 2003 ranged from 0·32 to 0·39 mm day⁻¹ with a mean ± s . d . of 0·35 ± 0·02 mm day⁻¹. These values were lower than the growth rates of leptocephali of other tropical eels such as Anguilla celebesensis or Anguilla borneensis , suggesting that A. b. bicolor from the eastern Indian Ocean have a longer leptocephalus period of oceanic migration.     

Variations in the migratory history of the tropical catadromous eels Anguilla bicolor bicolor and A. bicolor pacifica in south-east Asian waters

Fish movements between aquatic habitats of different salinity ranges (fresh, estuarine, marine) by the tropical catadromous eels Anguilla bicolor bicolor and A. bicolor pacifica were examined by analysing the otolith strontium and calcium concentrations of yellow (immature) and silver (mature) stage eels collected in south-east Asian (Indonesia, Malaysia and Vietnam) waters. The ratios suggest that all migratory-type eels, including freshwater, brackish water and marine residents, pass the river mouth. However, the habitat preference was different among the sites (countries). In Indonesia and Vietnam, most A. bicolor bicolor and A. bicolor pacifica were either marine or brackish water residents in this study. Alternatively, most A. bicolor bicolor were freshwater residents in Malaysia; such a typical catadromous migration pattern in these eels has not been found in previous studies. The wide range of otolith Sr:Ca in both subspecies indicates that the habitat use of these tropical eels was opportunistic among fresh, brackish and marine waters during their growth phases following recruitment to coastal areas. The geographical variability of migratory histories suggests that habitat use might be determined by the inter and intraspecific competition and environmental conditions at each site.     

Occurrence of exotic eels in natural waters of South Korea

We surveyed the proportion of anguillid eel species inhabiting South Korea natural waters. From September 2014 to August 2015, 429 eels were collected in various habitats for identification using morphological features and DNA-based molecular methods. We found 424 Japanese eels (Anguilla japonica, 98.8%), two European eels (A. anguilla, 0.5%), one American eel (A. rostrata, 0.23%), one tropical eel (A. marmorata, 0.23%), and one short-finned eel (A. bicolor pacifica, 0.23%). Three (A. anguilla, A. rostrata, and A. bicolor pacifica) are exotic species to the natural waters of South Korea; this study is the first record of their distribution in this region. Specifically, A. anguilla was found in the Lake Soyang and Cheongpyeong, while A. rostrata was found only in the Lake Cheongpyeong, and A. bicolor pacifica was found in the Geum River estuary.     

Light and electron microscopic studies on the enzyme cytochemistry of leucocytes of eels, Anguilla species

The leucocytes of three anguillid eels were studied using enzyme cytochemistry. Leucocytes were stained for peroxidase, alkaline phosphatase, acid phosphatase, aryl sulphatase, β-glucuronidase, N-acetyl-β-glucosaminidase, β-galactosidase, lysozyme, a variety of non-specific esterases, chloroacetate esterase and two proteases. All cells were negative for aryl sulphatase, β-glucuronidase, N-acetyl-β-glucosaminidase, and β-galactosidase. Very few neutrophils, thought to be mature, and all eosinophils contained peroxidase-positive granules, and some monocytes showed very weak peroxidase staining. All leucocytes lacked alkaline phosphatase, but all cells except lymphocytes and thrombocytes of A. dieffenbachii contained acid phosphatase. Neutrophil acid phosphatase released into phagosomes was associated with Escherischia coli bacteriolysis. Neutrophils also secrete lysozyme and, with monocytes, produce and secrete a variety of esterases. The possible interaction of lysozyme, acid phosphatase and esterases in bacteriolysis is discussed.     

Present and past genetic connectivity of the Indo‐Pacific tropical eel Anguilla bicolor

Aim The objective of this study was to reveal the present population structure and infer the gene‐flow history of the Indo‐Pacific tropical eel Anguilla bicolor. Location The Indo‐Pacific region. Methods The entire mitochondrial control region sequence and the genotypes at six microsatellite loci were analysed for 234 specimens collected from eight representative localities where two subspecies have been historically designated. In order to infer the population structure, genetic differentiation estimates, analysis of molecular variance and gene‐tree reconstruction were performed. The history of migration events and population growth was assessed using neutrality tests based on allelic frequency spectrum, coalescent‐based estimation of gene flow and Bayesian demographic analysis using control region sequences. Results Population structure analysis showed genetic divergence between eels from the Indian and Pacific oceans (F_ST = 0.0174–0.0251, P < 0.05 for microsatellites; Φ_ST = 0.706, P < 0.001 for control region), while no significant variation was observed within each ocean. Two mitochondrial sublineages that do not coincide with geographical regions were found in the Indian Ocean clade of a gene tree. However, these two sublineages were not differentiated at the microsatellite markers. The estimation of mitochondrial gene‐flow history suggested allopatric isolation between the Indian and Pacific oceans, and a possible secondary contact within the Indian Ocean after an initial population splitting. Bayesian demographic history reconstruction and neutrality tests indicated population growth in each ocean after the Indo‐Pacific divergence. Main conclusions Anguilla bicolor has diverged between the Indian and Pacific oceans, which is consistent with the classical subspecies designation, but is apparently genetically homogeneous in the Indian Ocean. The analysis of gene‐flow and demographic history indicated that the two mitochondrial sublineages observed in the Indian Ocean probably represent the haplotype groups of relict ancestral populations. A comparison with a sympatric congener suggested that absolute physical barriers to gene flow may not be necessary for population divergence in eels.     

Notes on the occurrence of the tropical eel Anguilla bicolor bicolor in Peninsular Malaysia, Malaysia

Previous studies indicated that a tropical freshwater eel Anguilla bicolor bicolor occurs in Africa, India, Sri Lanka, Bangladesh, Myanmar, Indonesia and Australia, but an intensive survey has indicated an extended distribution range for the species into Peninsular Malaysia. Thus, A. b. bicolor is a native subspecies of Malaysia.     

Migration and habitat use of the tropical eels Anguilla marmorata and A. bicolor pacifica in Vietnam

The patterns of use of marine and freshwater habitats by the tropical anguillid eels Anguilla marmorata and A. bicolor pacifica were examined by analysing the otolith strontium (Sr) and calcium (Ca) concentrations of yellow (immature) and silver (mature) stage eels collected in Vietnamese waters. In A. marmorata, the change in the Sr:Ca ratios outside the high Sr:Ca core was generally divided into three patterns: (1) typical catadromous life history pattern; (2) constant residence in brackish water; and (3) habitat shifting between sea and brackish waters with no freshwater life. In A. bicolor pacifica, no eels had a general life history as freshwater residents. The eels were also divided into three patterns: (1) constant residence in sea water; (2) constantly living in brackish water; and (3) habitat shifting from brackish to sea water with no freshwater residence. The mean Sr:Ca ratio value after recruitment to coastal waters ranged from 1.73 to 5.67 × 10^?3 (mean 3.2 × 10^?3) in A. marmorata and from 2.53 to 6.32 × 10^?3 (mean 4.3 × 10^?3) in A. bicolor pacifica. The wide range of otolith Sr:Ca ratios in both species indicated that the habitat use of these tropical eels was facultative among fresh, brackish, and marine waters during their growth phases after recruitment to coastal areas. Tropical eel species may have the same behavioural plasticity as temperate anguillid species regarding whether to enter freshwater or to remain in estuarine and marine environments.     

The influence of growth rate on the size of migrating female eels in Lake Ellesmere, New Zealand

Lake Ellesmere, a large coastal lake in the South Island of New Zealand, supports an important commercial eel fishery, based mainly on migrating (silver) male Anguilla australis . Lengths of silver female eels from samples collected in 1942, 1974–1982 and 1998–1999 showed an initial decline between 1942 and 1974 but an increase from 1979 onwards. Back-calculated growth rates of 50 female silver eels caught in 1998 showed that most (90%) exhibited a period of accelerated linear growth commencing at lengths between 380 and 660 mm (mean 598 mm); this accelerated growth coincided with a change in diet to piscivory. The onset of maturity was more closely associated with length than age, condition, or growth rate. The increase in average length of female silver eels of 250 mm over the past 20 years is consistent with the hypothesis that female eels adopt a size-maximizing growth strategy to ensure maximum fecundity; this is the first time this hypothesis has been demonstrated from temporal changes within a single population.     

Movement of exotic plants into coastal native forests from gardens in northern New Zealand

The anti-predator behaviours of a New Zealand freshwater crayfish (Paranephrops zealandicus) to the native long-finned eel (Anguilla dieffenbachii) and the introduced brown trout (Salmo trutta) were investigated. Crayfish modified their behaviour in the presence of both trout and eels. However, a significantly greater number of defensive chela displays and swimming responses were made to eels than trout. Crayfish were able to use chemical cues from skin mucus to detect eels but not trout. Paranephrops zealandicus is able to make some appropriate defensive behavioural responses to the introduced brown trout as well as to its native predator, the long-finned eel. However, crayfish may be at greater risk from the introduced predator because of their apparent inability to detect trout using non-contact chemical cues. This may be a reflection of the different co-evolutionary histories crayfish have had with trout and eels.     

Diel and seasonal feeding activity of the short-finned eel,Anguilla australis schmidtii,in Lake Ellesmere,Canterbury, New Zealand

Synopsis Eel samples from Lake Ellesmere, a brackish water lake in the South Island, New Zealand, were taken at approximately monthly intervals from January 1974 to April 1976. Nets were set for 24 h and emptied every three hours. Total lengths and stomach fullness values of 498 eels were recorded. Analysis using the non-parametric Kruskal-Wallis test showed that eels ⩽40 cm and 40.1–50 cm in length increased in fullness through the night with greatest fullness values at 0300 and 0600 h. Seasonal analyses revealed greatest eel activity in spring, summer and autumn. There was little eel activity in winter.     

A model to predict the presence of longfin eels in some New Zealand streams, with particular reference to riparian vegetation and elevation

Two logistic regression models were developed from a database of 27 biotic and physicochemical variables for 99 sites in the Taieri River, New Zealand, to predict the probability of occurrence of longfin eels. Average depth was associated positively with eels while woody debris and oxygen concentration were negatively associated. At a macro-scale probability of eel occurrence declined with increasing elevation and, for a given elevation, was higher in tussock and pasture catchments and lower in pine and native forest settings. Using a separate fish database for the Taieri River this macro-scale model predicted eel presence 95·4% in agreement with observation. A map was generated from the model showing areas of predicted high, moderate and low probabilities of eel occurrence. The model also estimated the minimum total number of eels present in the Taieri River catchment (excluding lakes, and streams below 100 m and above 1000 m) as 20 865 (95% CL: 10 560-36 350).     

Factors affecting recruitment of glass eels into the Grey River, New Zealand

The arrival pattern of glass eels of the shortfin eel Anguilla australis and longfin eel Anguilla dieffenbachii was studied over a two successive migration seasons in the Grey River, South Island, New Zealand. Fishing was carried out on selected nights during September to November, for 3 h per night during 2000 and 2001. The number of shortfin glass eels exceeded longfins in both years; earliest glass eels (September) were larger than later glass eels (November), and longfins larger than shortfins, but there were significant differences in size between years for both species. Environmental variables affecting recruitment differed between years, but common variables for both years were sampling date, time after high tide (incoming tide preferred), time after sunset and moon phase; the influence of moon phase appeared to be expressed both through tides (spring tides preferred) and moonlight. During the year of higher discharge variability, both increasing discharge and increased turbidity were also important.     

长薄鳅外周血细胞的显微结构和细胞化学特征研究

长薄鳅外周血细胞可分为红细胞、中性粒细胞、单核细胞、淋巴细胞和血栓细胞.在数量上,中性粒细胞、单核细胞、淋巴细胞和血栓细胞占白细胞总数的百分比分别是17.06%、5.83%、28.16%和48.94%.细胞化学染色显示所有白细胞均含有糖原物质,所有红细胞均不含酸性磷酸酶,中性粒细胞、单核细胞、淋巴细胞和血栓细胞均含有酸性磷酸酶.非特异件酯酶染色显示单核细胞呈阳性反应,中性粒细胞、淋巴细胞和血栓细胞均为部分呈阳性反应.所有细胞的碱性磷酸酶、过氧化物酶、苏丹黑显色反应均呈阴性.     

Eel community structure,fluvial recruitment of <Emphasis Type="Italic">Anguilla marmorata</Emphasis> and indication for a weak local production of spawners from rivers of Réunion and Mauritius islands

Anguillid eels were sampled from permanent rivers in the Réunion and Mauritius islands, western Indian Ocean, with a standardized electrofishing method. A. marmorata was very dominant, corresponding to 91.7 and 90.7% of all the eels collected in Réunion and Mauritius, respectively. Three other species (A. mossambica, A. bicolor bicolor and A. nebulosa labiata) were also present in both islands. A. marmorata showed a strong altitudinal gradient of densities from the lower to upper zones, especially in the younger stages (TL <250 mm), while A. mossambica was only found in the upper zones and A. bicolor bicolor occurred only in the lower zones (A. nebulosa labiata was rare). The eel species composition in freshwaters of both islands is very similar because these two adjoining islands are located in the same trail of drifting marine larvae. Mean estimated eel biomasses were noticeably low (11.1 and 22.2 kg ha⁻¹ in Réunion and Mauritius islands, respectively), especially when compared to those of other tropical insular systems without any eel fishery (Comoros or Polynesia, more than 100 kg ha⁻¹). Nevertheless, the fluvial recruitment of A. marmorata seemed to be regular during the surveyed period, staggering from October to April. The obvious lack of large eels in Mauritius but more significantly in Réunion suggests a high pressure from traditional fishery, and the local reproductive turnover is uncertain. Because sexual maturation seems to occur at a large body size for A. marmorata, as for temperate species, the Réunion and Mauritius rivers may only have a weak contribution to the regional production of spawners. However, the giant mottled eel population in the western Indian Ocean is believed to be panmictic at the regional scale, and may not rely exclusively on these islands’ contribution. A comparison is made with those of freshwater systems in other tropical islands.     

二色补血草的耐盐性研究

通过NaCl胁迫发芽试验、盆栽浇灌NaCl盐水试验、不同含盐量土壤的种植试验,研究二色补血草（Limoniumbicolor）3个时期的耐盐能力。结果表明：高浓度NaCl对二色补血草种子的萌发有明显的抑制作用,种子的发芽率与盐浓度之间呈显著的负相关,种子萌发时盐胁迫的适宜值、临界值、极限值分别是0.49%、1.30%、2.11%;盆栽试验结果表明,二色补血草在2.0%以下的NaCl盐水胁迫下没有表现明显的盐害症状,只表现高浓度NaCl胁迫下,生长量低于低浓度处理的,当处理浓度达到2.4%时,多数植株濒临死亡;不同含盐量土壤的种植试验结果表明,在自然条件下,二色补血草成株耐盐临界值为1.7%～1.8%。试验结果说明二色补血草具有较强的耐盐能力,适合在滩涂盐碱地推广种植。     

Global Spread of the Eel Parasite Gyrodactylus Anguillae (Monogenea)

Gyrodactylus anguillae is known from four continents, and intraspecific variation in the morphology of specimens from each continent is negligible. However, morphological characters alone may not always be adequate for recognizing populations that have been isolated geographically over evolutionary time. We were unable to obtain specimens from Northeast Asia, but G. anguillae collected from North America, Europe and Australia had identical ribosomal DNA sequences (ITS1-5.8SrRNA-ITS2 region). This lack of even minor genetic variation in populations from three remote continents leads us to conclude that they share a contemporary common ancestor. This is one of at least five pests of eels to have invaded new continents as a result of the eel trade in the last four decades; these other known eel pests include Pseudodactylogyrus spp. (Monogenea) and Anguillicola spp. (Nematoda). Their dispersal has probably been secondarily augmented by longshore migration of infected eels, and perhaps also by transportation in ballast waters. The only other known gyrodactylid from eel gills, G. nipponensis from Japanese eel, is not closely related to G. anguillae, because the ITS1 region of the former is short (370 bases) and that of the latter long (685 bases). G. anguillae probably originated in Europe, because it was recorded there over 40 years ago, before the development of the international eel trade. We predict that the worm has a high potential to invade eel populations in East Africa, Southeast Asia, and New Zealand.     

The behaviour of laying workers and the morphology and viability of their eggs in Melipona bicolor bicolor

Abstract. As in many other stingless bees, Melipona bicolor bicolor Lepeletier (Apidae: Meliponinae) workers lay two morphologically distinct types of eggs: slender ones that have a typical patterned chorion, and larger ones that lack this pattern. In this paper we report on the relation between egg morphology and the behaviour of the workers that lay such eggs. In most cases, the laying of each of these egg types is accompanied by a unique sequence of behaviours. After a worker has laid the unpatterned type of egg, she generally leaves the cell, giving the queen the possibility of eating this egg. In the case of the patterned egg type, the worker usually closes the cell immediately after her egg laying. When worker egg laying occurs right after a series of regurgitations, it stops the queen from ovipositing. When, instead, a worker lays an egg after queen oviposition, the cell contains two eggs. This study also revealed cases in which workers laid slender, patterned eggs without closing the cell, and other cases where workers laid large, spherical, unpatterned eggs and instantly closed the cell. Experiments in which worker eggs, destined to be eaten by the queen, were protected by covering the cell artificially with a piece of wax showed that some of these eggs developed into larvae, although they were occasionally relatively small. The occurrence of a range of combinations of egg-laying behaviours and egg morphologies in M. b. bicolor workers is discussed from the perspective of worker egg laying in other stingless bees.