Sodium fluoroacetate (1080) residues in longfin eels,Anguilla dieffenbachii,following exposure to contaminated water and food

Captive longfin eels (Anguilla dieffenbachii) were exposed to the vertebrate pesticide sodium fluoroacetate (1080) in the water column and through the ingestion of cereal pellet baits or possum muscle and gut tissue that contained 1080 residue. No mortality or unusual behaviour (in comparison with the controls) occurred in eels that were exposed to 1080. However, significantly greater weight loss occurred in eels exposed to 1080 compared with those eels that were not. No residue was detected in tissues of eels exposed to 1080 cereal baits through ingestion and direct (dermal and respiratory) absorption, or through direct absorption only. Low concentrations of 1080 were detected in muscle tissue of eels that consumed contaminated possum muscle (x = 0.0174 μg/g) or gut (x = 0.0306 μg/g) tissue. The primary factors affecting the concentration of 1080 detected in eel tissue included the dose of 1080 (mg/kg) that each eel" receiveddate="and number of days since the eel last fed on contaminated tissue. Based on the 1080 concentrations measured in eels in this study, the risk of acute poisoning to humans from eating contaminated eel flesh is considered extremely low. Even so, national and international perceptions and food safety standards have the potential to limit eel exports and/or close an eel fishery if 1080 residue was discovered in tissue.     

Effect of size grading on the growth performance of shortfin eel (Anguilla australis) during its yellow stage

It is generally believed that size grading in a fish farm improves the total biomass output, because it will minimise the stress imposed by larger individuals over small individuals, resulting in higher feed intake and growth rate. The objective of this study was to evaluate the effect of size grading on individual growth performance of yellow New Zealand shortfin eel (Anguilla australis). A 109 day trial was conducted in a recirculation aquaculture system (RAS) with 103 eels of similar initial weight (101 ± 12 g). All eels were individually marked by PIT (passive integrated transponder) tags. On day 42, eels were graded to establish the following groups: only small eels (S-graded ≤ 135 g), only large eels (L-graded > 135 g), and small and large eels together (S-ungraded and L-ungraded). The large eels showed better specific growth rate (SGR), feed intake (FI) and feed conversion ratio (FCR) than the small eels. Nevertheless, no significant differences were found either between L-graded and L-ungraded or between S-graded and S-ungraded. The age of eels was not significantly different between groups. These findings suggest that the individual growth rate performance of the eels is not primarily a consequence of social interaction among tank-mates.     

Variation in organotin accumulation in relation to the life history in the Japanese eel Anguilla japonica

In order to examine the ecological risks caused by organotin compounds (OTs) in diadromous fish migrating between sea and freshwaters, tributyltin (TBT) and triphenyltin (TPT) compounds and their breakdown products were determined in the catadromous eel Anguilla japonica, which has sea, estuarine and river life histories, collected in Japanese sea, brackish and freshwaters within the same region. Ontogenic changes in otolith strontium (Sr) and calcium (Ca) concentrations were examined along the life history transect to discriminate the migration type. There were generally three different patterns, which were categorized as ‘sea eels’, ‘estuarine eels’ and ‘river eels’ according to the otolith Sr:Ca ratio. The concentrations of TBT in silver eels (mature eels) were significantly higher than that in yellow eels (immature eels), and the percentages of TBT were also higher in silver eels than in yellow eels. A positive correlation was found between TBT concentration and the gonad-somatic index (GSI). It is thus considered that silver eels have a higher risk of contamination by TBT than yellow eels. TBT and TPT concentrations in sea eels were significantly higher than those in river eels, while no significant differences were observed in TBT and TPT concentrations in estuarine eels compared to sea and river eels. These results suggest that sea eels have a higher ecological risk of OT contamination than river eels during their life history, and the risk of OTs in estuarine eels is considered to be intermediate between that of sea and river eels. Positive linear relationships were found between Sr:Ca ratios and the concentrations of TBT and TPT. Therefore, these results suggest that the ecological risk of OTs increase as the sea residence period in the eel becomes longer. TBT and TPT concentrations in sea eels were significantly higher than those in river eels even at the same growth stage. Thus, it is clear that migratory type is the most important factor for OT accumulation during the life history.     

Locomotor activity rhythm in the Japanese eel Anguilla japonica elvers

Under artificial LD cycles(6,12,18 L),the elvers of Japanese eel,Anguilla japonica,showed a 24 h cycle of locomotor activity rhythm being most active at light transitions:the eels' activity rose to a primary peak after lights-off,followed by a quiescent period during which they buried into the shelters or lying motionlessly on sand for most of the time,and then reached a secondary peak before lights-on.Elvers could resynchronize their activity rhythm with a new photo cycle within 4 d.Moreover,their activity level at dark phase significantly increased as the light period was prolonged:higher activity levels during shorter dark period.However,the elvers did not display clearly the existence of a circadian rhythm under constant light or dark conditions.The timing of daily activity rhythm evidenced in the Japanese eels may occur through the action of the LD cycles with a weak participation of an endogenous circadian system.In all the LD cycles,over 99% of the activity occurred in the dark phase,indicating that the eels were always nocturnally active no matter what time of day it might be.Under 12 L conditions,the eels' activity level and the time outside sand were significantly elevated both at light and dark phases as temperature increased from 10~15 to 20~25 ℃.The activity rhythm pattern(i.e.,two peaks occurring around light transitions) did not apparently change among temperatures.However,in contrast with the primary activity peaks immediately after lights-off at 20 and 25 ℃,the timing of the primary peaks at 10 and 15 ℃ showed a latency of a few hours following lights-off,indicating the inhibiting effect of low temperature on the eels' activity.     

Trace metals in Japanese eel Anguilla japonica in relation to ecological migratory types and growth stages

In order to understand the metal concentrations in Japanese eel Anguilla japonica, nine elements were analyzed in the livers of different migratory types of eels collected from Tokushima region (south Japan). Migratory types were defined by examining the Sr:Ca ratio in otoliths. The results showed that there were significant differences in V, Cr, Cd, and Pb concentrations among the migratory types. Mature-sea-eels show a higher risk of metal accumulation than other migratory types of eels, and the concentrations of Mn, Cu, and Zn in mature eels were significantly higher than those in immature eels. The study suggests that the eel liver is a valuable bioindicator for trace metals; however, when using the eel as a bioindicator to reveal the pollutants in aquatic systems, life history analysis should be carried out for accurate interpretation of the results.     

First record of male freshwater eels (Anguilla dieffenbachii) caught at sea

Two silver (migratory) male freshwater eels, Anguilla dieffenbachii, were caught in a commercial trawl net in the South Taranaki Bight in April 2014. The capture date and the relatively small eye size indicated that both eels had probably only recently entered the sea. This is the first record of male A. dieffenbachii caught at sea, en route to the presumed spawning area in the South Fiji Basin.     

中国近海洄游日本鳗鲡(Anguilla japonica)玻璃鳗肠道微生物菌群分析

为研究长江口日本鳗鲡玻璃鳗肠道菌群的结构与多样性特征,初步探究野生鳗鲡仔鱼的营养需求,分别采集浙江台州市、舟山市以及江苏盐城市邻近海域的玻璃鳗样品,利用16S rDNA扩增子测序技术,分析三个采样点玻璃鳗肠道优势菌群及营养代谢相关的功能差异。结果显示,三个采样点的玻璃鳗肠道菌群均以变形菌门(Proteobacteria, 68.7%～82.0%)和放线菌门(Actinobacteria,4.2%～19.0%)为主要优势菌门。在属分类水平上,不动杆菌属(Acinetobacter, 12.4%～17.3%)和假单胞菌属(Pseudomonas, 8.07%～13.03%)丰度较高,属固定优势菌属。此外,每个采样点样本中都含有丰富的独特细菌群,包括台州市的气单胞菌属(Aeromonas)、舟山市的内生单胞属(Endozoicomonas)和丙酸杆菌属(Cutibacterium)以及盐城市的嗜冷杆菌属(Psychrobacter)和稳杆菌属(Empedobacter),推测是受采样点不同水环境因素影响。不动杆菌、假单胞菌、内生单胞菌等菌属在多种鱼类肠道中有着消化蛋白质的功能,气单胞菌虽属于...     

Fish community responses to invasive fish removal and installation of an exclusion barrier at Lake Ohinewai,Waikato

Introduced common carp (Cyprinus carpio) are a recognised threat to New Zealand’s freshwater ecosystems. In 2011, an invasive fish removal programme was undertaken in 16.8 ha Lake Ohinewai, a Waikato riverine lake. Active fish removal using netting and boat electrofishing was supported by installation of a one-way exclusion barrier on the outflow to Lake Ohinewai. The barrier was designed to allow fish passage downstream out of the lake, while preventing adult carp from moving upstream. The estimated carp population was reduced from 8,548 fish (5,863–12,937, 95% confidence limits) in 2011–454 fish (251–889, 95% CL) in 2014. However, by 2016 the carp population had recovered to 2,063 fish (1,070–4,328, 95% CL) with increased abundance in invasive brown bullhead catfish (Ameiurus nebulosus) also observed. This research demonstrates that carp populations can be reduced to low abundances in the short to medium term, but continued removal will be required for on-going control.     

Effect of estradiol-17β on pituitary-thyroidal axis of Japanese eel (Anguilla japonica)

In teleost sPeCies, it is well accepted that estradiol--l75 (E2 )is generated from ovarian fOl-licles stimulated by pituitary gonadOtropins (GTH) (Nagahama, l987). FUrthermore, E2 canstimulate hepatic vitellngenesis and elevate plasrna yOlk protein precursor vite1lOgenin, totalCa and W levels in several teleosts (KorSgaard and Petersen, l976, l978; Whiteheadet al., l978; Elliott et al., l979; Pertersen et al., l983; Wallace, 1985; tapigliati etal., 1999). On the other hand, many stud…     

Prey selection and dietary overlap of shortfinned (Anguilla australis) and longfinned (A. dieffenbachii) eels during summer in the Horokiwi Stream,New Zealand

Benthic macroinvertebrates were collected and the diets of shortfinned eels (Anguilla australis) and longfinned eels (Anguilla dieffenbachii) inhabiting a small coastal New Zealand stream were examined to investigate intraspecific and interspecific trophic partitioning and prey selection. Our results showed intraspecific segregation of preferred prey among three size classes of juvenile shortfinned eels, but there was significant overlap between different size classes of longfinned eels. All size classes of both species of eel fed nocturnally on similar prey, and so there was no indication of temporal or trophic segregation. Therefore, habitat separation is assumed to be the main mechanism to reduce interspecific competition in these two co‐occurring species of eels.     

Reexamination of the spawning migration of Anguilla dieffenbachii in relation to water temperature and the lunar cycle

ABSTRACT

The oceanic spawning migration of female Anguilla dieffenbachii eels was previously studied using pop-up satellite transmitting tags (PSAT). The swimming depths and experienced-temperature data of 3 eels released in May 2006 were re-examined in relation to water temperature data, and also lunar cycle and regional hydrography as these latter aspects were not considered in the original study. Eel 2 and Eel 3 initially experienced lower water temperature above 600?m, suggesting they remained south of the subtropical-convergence front longer than Eel 1. Their experienced nighttime minimum depths showed linear relationships with the lunar cycle, because they swam shallower during new moon than during full moon. The eels experienced narrow deep-day temperature ranges at a wide range of depths compared to experiencing narrow shallow-night depth ranges where temperatures varied more widely, indicating that several different factors determine their day and night depth ranges.     

Induction of cytochrome P4501A and biliary PAH metabolites in European eel Anguilla anguilla: Seasonal, dose- and time-response variability in field and laboratory conditions

Induction of cytochrome P4501A in fish is a well-known indicator of exposure to polycyclic aromatic hydrocarbons (PAHs) and determination of PAH metabolites in bile by fixed wavelength fluorescence (FF) or synchronous fluorescence spectroscopy (SFS), has become an useful method in monitoring programs. In this work the relationship between cytochrome P4501A (EROD activity) and levels of biliary PAH metabolites was measured in the European eel Anguilla anguilla, in both field and laboratory conditions: organisms were sampled on a seasonal basis from the Orbetello lagoon (Tuscany) to characterize the natural variability of these biological parameters, while in laboratory eels were intraperitoneally injected with benzo[a]pyrene to investigate temporal and dose-dependent induction patterns. Results showed that induction of cytochrome P450 and accumulation of PAHs metabolites in bile are not necessarily correlated either in field, or in laboratory investigations; different seasonal changes were measured in natural conditions and slight variations in dose and time response patterns were also obtained in laboratory exposures.     

Summer spatial patterns of the fish community in a large,shallow, turbid coastal lake

Several water quality parameters, marginal vegetation, and the fish community in Lake Ellesmere, a large, shallow, turbid lake situated on the east coast of the South Island, New Zealand, were sampled along selected transects in late summer to determine species spatial patterns. Thirteen species offish were caught, with seven of them comprising major populations, although only four of these were adequately sampled by the method used—they included inanga (Galaxias maculatus), common smelt {Retropinna retropinna), shortfinned eel (Anguilla australis), and common bully (Gobiomorphus cotidianus). Inanga were almost exclusively confined to areas on the western side of the lake which has a convoluted shoreline with a variety of small embayments with scattered vegetation along the margins. Common smelt occupied both marginal and offshore areas, but they too were more abundant along the margins particularly on the western side. Both the common bully and shortfinned eel were widespread and abundant in the lake, although their abundance and biomass were higher within the vicinity of the lake outlet, major inflowing tributaries, and other marginal habitats. All three species of flounders of the genus Rhombosolea were poorly represented in our samples. However, in commercial catches they were reasonably abundant, with the sand flounder (R. plebeia) and yellowbelly (R. leporina) being more common in offshore than inshore catches, whereas the black flounder (R. retiaria) showed no difference in the catches between areas. Our overall findings are consistent with the hypothesis that bottom‐dwelling species (eels, bullies, flounders) are more widely distributed than free‐swimming forms (inanga, common smelt), which were largely confined to areas sheltered from prevailing winds. The highly turbid nature of the lake, primarily because of re‐suspension of fine bottom sediments by frequent winds, is considered an important factor in the distribution of the fish fauna.     

Invasion of a New Zealand freshwater stream by glass‐eels of two Anguilla spp.

Recruitment of glass‐eels into freshwater is in two distinct phases characterised by behavioural differences: an initial invasion from the sea, and an upstream migration. Catches made at night in the Makara Stream, Wellington (41° 13'S, 174° 43’ E) indicate that the invasion by both New Zealand species commences in July, with that of the long‐finned eel Anguilla dieffenbachii Gray finishing by November, and that of the short‐finned eel A. ausiralis schmidlii Phillipps by December.

The length of post‐metamorphic sea‐life influences both morphology and behaviour of the glass‐eels. Differences in this period of sea‐life between early and late season glass‐eels explain the initial avoidance but later attraction of fresh water to the glass‐eels. Responses to fresh water also explain the preference for early season glass‐eels to invade on the flood tide and late season glass‐eels on the ebb tide. Neither the lunar cycle nor rainfall appear to be significant influences on invasion periodicity.     

长江口环境条件对日本鳗鲡(Anguilla japonica)鳗苗溯河洄游的影响

长江口是日本鳗鲡鳗苗的手要产区,利用2007年1-5月在长江口的长兴岛、横沙和杭州湾小洋山4个取样点得到的日本鳗鲡鳗苗渔获量数据,初步研究了鳗苗的补充时间分布以及补充量与潮汐、月相等环境因素之间的关系.发现鳗苗在长江口的补.充时间从1月下旬开始到5月中旬结束,鳗苗日产量峰值出现日期从长江口外向内逐渐推迟,与其洄游路线致.长江口附近潮汐为半月潮,每月有两次涨落潮,鳗苗溯河量与潮汐周期呈现一定的节律性,每月有两次鳗苗峰值.河口区鳗苗溯河具有潮流选择性,长江口内鳗苗溯河量起汛潮多于落汛潮:长江口外鳗苗溯河量和潮汐振幅呈现正相关趋势.日本鳗鲡鳗苗的溯河量与月相变化也有一定的关系;朔月望月的平均单网捕捞量之和占总平均单网捕捞量的93.13%,而上下弦只占6.87%.经过方差检验,朔月鳗苗溯河量多于望月,且二者之间存在极显著差异(P<0.01).     

鳗鲡目鱼类线粒体蛋白质编码基因易位及系统演化关系分析

鳗鲡目鱼类线粒体基因组的基因组成较为保守,在58个线粒体基因组中,仅有3个物种存在基因数量的差异。在19个鳗鲡目鱼类线粒体基因组中存在主编码基因的重排。主编码基因的变异位点分析结果支持nad5、nad4和nad2基因作为cox1和lrRNA基因辅助的分子标记。鳗鲡科Anguillidae的20个种(亚种)聚在一起,强烈支持鳗鲡科为单系群(BPP=100)。鳗鲡科下属的3个类群(大洋洲类群、大西洋类群和印度洋-太平洋类群)也同时得到有力的验证(BPP均为100)。线鳗科Nemichthyidae和锯齿鳗科Serrivomeridae亲缘关系最近,二者聚类后,与鳗鲡科Anguillidae构成姊妹群(BPP=100)。在囊喉鱼亚目Saccopharyngoidei中,宽咽鱼科Eurypharyngidae与囊鳃鳗科Saccopharyngidae聚类(BPP=100),同时,单颌鳗科Monognathidae与月尾鳗科Cyematidae聚类(BPP=100),4个科聚在一支,支持囊喉鱼亚目为单系群(BPP=100)。在囊喉鱼亚目线粒体基因组中,3个物种(吞鳗Eurypharynx pelecanoides、拉文囊鳃鳗Saccopharynx lavenbergi和杰氏单颌鳗Monognathus jesperseni)存在主编码基因的重排。16种鳗鲡(细美体鳗Ariosoma shiroanago、短吻颈鳗Derichthys serpentinus、凯氏短尾康吉鳗Coloconger cadenati、鸭颈鳗Nessorhamphus ingolfianus、龟草鳗Thalassenchelys sp.、粗犁齿海鳗Cynoponticus ferox、百吉海鳗Muraenesox bagio、巨斑花蛇鳗Myrichthys maculosus、大吻沙蛇鳗Ophisurus macrorhynchos、几内亚副康吉鳗Paraconger notialis、哈氏异康吉鳗Heteroconger hassi、小头鸭嘴鳗Nettastoma parviceps、弱头鳗Leptocephalus sp.、斑点长犁齿鳗Hoplunnis punctata、尖吻小鸭嘴鳗Facciolella oxyrhyncha和星康吉鳗Conger myriaster),与鳗鲡目线粒体主编码基因的原始排列相比,共享nad6基因的易位。同时,基于线粒体基因组13个蛋白质编码基因构建的系统演化树,强烈支持这16个物种聚为一支(BPP=100)。然而,由此而带来的海鳗科Muraenesocidae、拟鯙科Chlopsidae和糯鳗科Congridae是否为单系群的问题,值得今后深入探究。     

Is feeding behaviour related to glass eel propensity to migrate?

Several studies have shown that eel diadromy is facultative and that migratory divergences may appear during glass eel estuarine migration. The origin of the differences in migratory behaviour among glass eels remains unclear but initial evidence supports the role of individual energetic and thyroidal status. Even if starvation is usually associated with glass eel migration, feeding does seem to occur in some glass eels. The aim of the present study was to investigate feeding behaviour and glass eel growth in relation to the propensity to migrate. Feeding rate and weight gain were higher in fish having a high propensity to migrate (M⁺ fish) than in fish having a low propensity to migrate (M⁻ fish) in fed glass eels, whereas no clear difference in the variation in body weight was observed among unfed fish (controls). M⁻ fish initially had lower percent dry weight than M⁺ fish, which suggests a link between appetite, propensity to migrate, and energy content. We discuss the role played by endocrine signals on these processes. In fish, thyroid hormones contribute to the control of growth and development. In addition, they play a role in flatfish and leptocephalus metamorphosis and appear to be involved in smolt and glass eel migratory behaviour. As such, they represent a good candidate which would promote the propensity to migrate as well as digestive system development. Their role in the hormonal control of food intake however remains vague.     

鳗鲡(Anguilla japonica)性腺发育和饥饿胁迫下生物学指标及体内蛋白质与氨基酸含量变化

自然条件下, 鳗鲡(Anguilla japonica)自降河入海至性腺发育成熟需洄游数千公里、耗时半 年以上, 且整个过程中不摄食。本文以降海洄游、人工促熟和长期饥饿(20 个月)三种状态下的鳗鲡 为材料, 研究其在性腺发育和饥饿胁迫时的主要生物学指标(包括肥满度、肝体比、脏体比、性腺指 数、含肉率)以及肌肉、肝脏和性腺中的粗蛋白与氨基酸含量的变化情况, 以探讨鳗鲡性腺发育和饥 饿胁迫下的营养物质来源与变化。结果发现: 人工促熟鳗鲡的肝体比、脏体比和性腺指数显著高于 降海洄游鳗鲡(P<0.05), 而含肉率、肝脏和卵巢内的粗蛋白含量、氨基酸总量、必需氨基酸总量以及 非必需氨基酸总量均显著低于降海洄游鳗鲡的含量(P<0.05); 长期饥饿鳗鲡的肥满度、肝体比、含肉 率、肌肉(鲜样)、肝脏内的粗蛋白、氨基酸总量、必需氨基酸总量以及必需氨基酸占氨基酸总量的 比值显著低于降海洄游鳗鲡(P<0.05).结果表明, 鳗鲡性腺发育所需要的营养物质主要来源于肌肉, 其性腺的发育依赖自身营养物质在体内的流动和转化, 肌肉中的必需氨基酸和非必需氨基酸均被利 用, 转化成性腺发育所需要的物质。     

Blood oxygenation in shortfin eels during swimming and hypoxia: Influence of the root effect

Blood samples were withdrawn from dorsal aortic cannulae in shortfin eels before, during, and after acute exposure to hypoxia and to forced swimming. Both hypoxia (PIO₂ < 40 mm Hg) and forced swimming at 24 cm s^‐1 abolished apnoeic periods and increased ventilation. The fall in PaCO₂with hyperventilation, raised pH and thus increased the oxygen carrying capacity of arterial blood. The Root effect influences shortfin eel blood up to pH 8.0, at 17°C and has an effect on arterial oxygen content. It cannot be responsible for all of the increased oxygen content during swimming and in recovery from swimming and hypoxia; ventilatory and/or circulatory changes must account for the rest. Hypoxia, but not swimming, produced a rise in dorsal aortic blood pressure. The bradycardia of hypoxia was deeper than that which accompanies apnoeic periods in air‐saturated water.     

Effects of riparian manipulation on stream communities in small streams: Two case studies

The effects of riparian manipulation in New Zealand are described for two case studies, one a short‐term study of the effects of the removal of riparian vegetation on fish, and the second, a long‐term study of the effect of re‐establishment of riparian vegetation on fish and benthic macro invertebrates. The first case study was an experiment carried out between November 2001 and May 2002. Overhanging bank vegetation and in‐stream wood were removed from short reaches of a small pastoral stream that had intact riparian margins, resulting in a change in stream structure with the formation of shallow uniform runs rather than pool and riffle structures as in unmodified reaches. The removal of bank cover and consequential instream habitat changes reduced inanga (Galaxias maculatus) densities by a factor of four within months of vegetation removal, showing the importance of instream cover and habitat to inanga. Adult longfin eel (Anguilla dieffenbachii) also became less abundant in the cleared reaches, but elvers (Anguilla spp.) became more abundant. In the second case study, pastoral sections in two small streams draining from native forest catchments were restored in 1995/96 by planting riparian vegetation and preventing stock access. After 10 years, the restoration efforts had more than doubled the numbers of giant kokopu (G. argenteus) and redfin bullies (Gobiomorphus huttoni), slightly increased numbers of banded kokopu (G. fasciatus), and decreased shortfin eel (A. australis) numbers by about 40%. The macroinvertebrate communities changed so that they became more similar to those at upstream native forest reference sites. These two case studies show that riparian margins can influence the composition of the fish and macroinvertebrate communities in small streams through the effects on cover, instream habitat and probably water temperature. Riparian restoration was most effective for the fish species that use cover and pool habitat.