Eel Anguilla Research Articles

Dietary lipid concentrations influence growth, body composition, morphology of the liver and mid-intestine, and antioxidant status of marbled eel (Anguilla marmorata)

An 8-week feeding trial was conducted to explore the effect of dietary lipid concentrations on growth, body composition, morphology of liver, and mid-intestine and antioxidant status in marbled eel (Anguilla marmorata). Fish (initial average weight 6.86 ± 0.11 g) were held in 18 tanks (inside diameter 80 cm, height 60 cm, volume 300 L, 25 fish/tank), with triplicate treatment groups being fed to apparent satiation twice each day on isonitrogenous (421 g/kg crude protein) diets containing different concentrations of lipid (41.2, 73.9, 113.9, 146.2, 178.1, and 216.7 g/kg). The sampling procedure was implemented after 24 h of fasting. Fish fed the diets with 178.1 and 216.7 g lipid/kg grew better than fish fed the other diets. The lowest feed intake and the highest feed conversion rate were found in 41.2 g/kg group. Muscle lipid concentrations and heights of intestinal folds, enterocytes, and microvilli in mid-intestine increased as dietary lipid concentrations increased from 41.2 to 178.1 g/kg. Hepatocyte hypertrophy and lipid vacuolization were seen in liver of the fish fed 216.7 g/kg diet. Based on broken-line analysis of serum total antioxidant capacity and quadratic regression analysis of serum glutathione peroxidase and catalase, it was concluded that dietary lipid concentrations of 125.5–159.2 g/kg promoted antioxidant status. A broken-line analysis of data for specific growth rate and weight gain gave an estimated optimal dietary lipid concentration of 195.3–198.7 g/kg. Marbled eel had quite a high demand for dietary lipid to support good growth, but excessive lipid level (216.7 g/kg) may have an adverse impact on liver structure. Moreover, marbled eel may not tolerate high concentration of dietary carbohydrate.

Recolonisation of a fish and invertebrate community in a wetland following a drought: the importance of deep water refugia

ABSTRACT Wetland restoration or re-establishment is a common conservation goal, and the ability of a wetland community to recover from events such as drought are key to its long-term success. At the mouth of the Waiau River in Southland, New Zealand, a series of wetland ponds have been created by diverting water from the river. A period of particularly low river flows resulted in the wetland drying out entirely, except for a few deep channels. A subsequent flood inundated the ponds, creating an opportunity to study recolonisation of the system. The deep channels provided an important refuge habitat for eels (Anguilla spp.) during dry periods, with significantly higher numbers close to the channels immediately after refilling than at sites further away. Smaller fish (Gobiomorphus and Galaxias spp.) took much longer to reappear in the ponds. The macroinvertebrate community showed no significant variation over the short term or up to a year post-refill, although individually snail and water bug taxa increased and microcrustaceans decreased in abundance. Daphnia and ostracods were observed soon after refilling and dominated the community. This study highlights the importance of spatial heterogeneity in constructed wetland systems, as this habitat variation likely increases the recovery rate after drying.

Development and evaluation of an empirical equation for the screening effect of bar racks

Passage through hydropower plants can cause severe injuries for downstream migrating fish. Bar racks and bypass systems can help to protect fish from turbine-induced mortality if they are designed correctly following guidelines. Currently, it is not possible to assess how effective bar racks are that do not meet design criteria for fish protection. We introduced the screening effect as a performance parameter for bar racks and developed an equation for determining the screening effect of bar racks for silver eels based on an empirical approach. We compared the equation for eels with the results of behavioural laboratory studies with European eels (Anguilla anguilla), roach (Rutilus rutilus) and Atlantic salmon smolts (Salmo salar). We showed that the equation is not applicable for roach and Atlantic salmon smolts. Using univariate statistics, we identified a significant influence of the bar rack spacing on the screening effect for eels for the guidance system with (Kruskal-Wallis test, p = 0.002) and without a bypass (Kruskal-Wallis test, p = 0.0220) and for salmon without a bypass (Kruskal-Wallis test, p = 0.001) for a significance level of 0.05. The screening effect was significantly different between the fish species tested for a bar rack without bypass and 20 mm bar rack spacing (Kruskal-Wallis test, p = 0.003) and 40 mm (Kruskal-Wallis test, p < 0.001) as well as a bar rack with a bypass and either 40 mm bar rack spacing (Kruskal-Wallis test, p = 0.014) or 60 mm (Kruskal-Wallis test, p = 0.001). The results can help to perform biological evaluations and plan retrofitting measures of non-optimal bar racks.

Estimations of Riverine Distribution, Abundance, and Biomass of Anguillid Eels in Japan and Taiwan Using Environmental DNA Analysis.

Although populations of anguillid eels have declined remarkably in recent decades, monitoring data on the spatial and temporal variation in their dynamics are often limited, particularly for tropical eel species. As there are often sympatries of multiple eel species in tropical rivers, identifying eel species based solely on morphological characteristics is challenging. Basin-scale surveys were conducted in rivers of southern Japan and northern Taiwan to investigate (1) whether the spatial distribution, abundance, and biomass of the tropical eel species, the giant mottled eel (Anguilla marmorata), can be monitored in rivers by comparing the results obtained from environmental DNA (eDNA) analysis with data from electrofishing and (2) the riverine distribution of the sympatric A. marmorata and the temperate eel species, the Japanese eel (Anguilla japonica), in this region using eDNA analysis. Although we found an much lower abundance of A. marmorata in the study region, we identified the eDNA of the species from all of the study sites (21 sites) where it was collected by electrofishing, in addition to 22 further study sites where it was not collected directly. This indicates that eDNA analysis has a greater sensitivity for detecting A. marmorata, making it a powerful tool for monitoring the spatial distribution of the species in rivers. We found a significant positive relationship between eDNA concentration and both the abundance and biomass of A. marmorata, and eDNA concentration seemed to better reflect the abundance of the species than did biomass. eDNA of both A. japonica and A. marmorata was identified from almost all rivers, indicating the sympatry of these species in this region, although the degree of sympatry differed between rivers. Though the eDNA concentration of A. japonica decreased significantly with increasing distance from the river mouth, no significant relationship was found for A. marmorata. This study is the first to demonstrate the potential usefulness of eDNA analysis for estimating the spatial distribution, abundance, and biomass of tropical eels in rivers and to further apply this method to investigate sympatry among anguillid species. eDNA analysis can help in obtaining data on the population dynamics of tropical eels, providing invaluable information for managing these species.

Effects of Probiotic Dosage on Water Quality, Total Count of Aeromonas spp. and Pseudomonas spp. in Eel Anguilla bicolor Cultivation

This study was carried out to evaluate the effects of probiotic dosage on water quality, total number of Aeromonas spp. and Pseudomonas spp., in eel (Anguilla sp.) cultivation. Experiment was conducted by using fiber glass tanks (1x1 m2) with 800 L water volume. Eel fingerling with 50 g average body weight were stocked at a density of 20 eel/tank in triplicates. Observation was conducted on total number of bacteria and water quality. The results indicated that the total bacterial count increased gradually by the time of cultivation with highest density of 1.49x107 cfu/mL. Probiotics at a dose of 40 mL/tank weekly increased the total count of bacterial cells in water. Probiotic application was able to decrease the total number of both Aeromonas spp. from 1.95 x 105 to 5.44 x 104 cfu/mL, and Pseudomonas spp. from 3.57 x 104 to 8.1 x 103 cfu/mL. Water quality during this study was not significantly affected by the application of probiotic. This result suggested that the application of proper dose probiotics suppresses Aeromonas spp. and Pseudomonas spp. cells density in water, and might decrease the bacterial infections in eel culture.

Artificial reproduction of Anguilla anguilla: evaluation of biometrics characteristics of a population from Valle Campo Lagoon, Comacchio (Italy)

One of the major problems in artificial eel reproduction is identification of broodstock with high performance reproductive characteristics. The aim of this study was to study population characteristics and the reproductive potential of eels (Anguilla anguilla) located in Valle Campo valley (Comacchio, Italy). A total of 200 eels/period (spring–summer and autumn–winter) were measured to obtain an external indicator of their maturation state. Morphometric parameters were used to calculate condition factor (K), eye index (EI) and pectoral fin length index (PFLI). Silver index analyses showed the lack of silver males and of fully mature females. Most represented females were yellow females at stage II. Silver females represented 27.9% of the population. Seasonal analysis shows how temperature reduction favoured the presence of silver females versus yellow females. Statistical analysis of EI, cranial (CI), PFLI and gonadosomatic (GSI) indexes showed that significant differences were found for EI, CI, PFLI and GSI between yellow and silver eels. No significant difference was found between stage III and IV silver eels, while a significant difference for EI was found between stage I and II yellow eels and for IC at stage II with respect to all other stages. The present study defined how Valle Campo could present environmental and trophic conditions which could favour precocious development of a population of silver females with a noticeable reproductive potential, to be used in open sea release or in artificial reproduction programmes. On the contrary, the valley seems to present unfavourable conditions for both development and sexual maturation of male eels.

Exploring perceptions to manage conflicts: The case of the European eel fishing moratorium in Southern Spain

ABSTRACTThis article presents results of a qualitative study on the opinions and attitudes of stakeholders of the areas affected by the moratorium on European eel (Anguilla anguilla) fishing (declared in 2010) in the Guadalquivir River marshlands of southern Spain. Results suggest that the stakeholders were sustaining different principles, criterions, and proposals that frequently conflicted because problems with mutual understanding. The usefulness of these results to manage this conflict is also discussed. This research allowed for improving communication, channeling demands of the different stakeholders, and searching for negotiated solutions to reduce the tensions that arose after the moratorium. Results have been shown to be especially relevant in this case where some stakeholders held strong and conflicting positions that made the dialogue almost impossible given that eel fishing was being carried out illegally.

Changes in Sex Steroids and Ovarian Steroidogenic Enzyme mRNA Levels in Artificially Maturing Japanese Eel (Anguilla japonica) and Naturally Maturing New Zealand Longfin Eel (Anguilla dieffenbachii) during Vitellogenesis

Repeated hormone injections are routinely used to induce advanced stages of oogenesis in freshwater eels, but this approach may result in aberrant germ cell development. To investigate the underlying causes, levels of sex steroids (testosterone, T; estradiol-17β, E2) and ovarian steroidogenic enzyme mRNAs were compared between artificially maturing Japanese eels and wild-caught, spontaneously maturing New Zealand longfin eels. The latter were employed as reference, as wild Japanese eels in advanced stages of oogenesis are near-impossible to catch. Serum T levels in artificially maturing Japanese eel changed with stage in a pattern that was comparable to that in longfin eels. Likewise, ovarian mRNA levels of most steroidogenic enzyme genes were not qualitatively dissimilar between both eel species when taking developmental stage into account. However, aromatase (cyp19a) mRNA levels, together with serum E2 levels, rapidly increased in artificially maturing Japanese eels in mid-late stages of oogenesis (gonadosomatic index, GSI = 13.8%), whereas no such increase was evident in longfin eels (GSI ~ 6.9%). In addition, sex steroid and target gene mRNA levels fluctuated drastically with each hormone injection. We contend that expression of most target genes, possibly even that of cyp19a, during induced oogenesis could be “normal”, with the drastic fluctuations due most likely to hormone delivery through repeated injections. The effects of these fluctuations on gamete quality remain unknown and resolving this issue may prove fruitful in the future to further artificial propagation of anguillid eels.

Habitat Partitioning and its Possible Genetic Background Between Two Sympatrically Distributed Eel Species in Taiwan.

The geographical distributions of the Japanese eel (Anguilla japonica) and Giant-mottled eel (A. marmorata) overlap in many regions in East Asia and therefore suffer from interspecific competition in the same rivers. After a long period of adaptation, the Japanese eel and Giant-mottled eel may exhibit habitat partitioning in the rivers to diminish the interspecific competition between them. In this study, we conducted a field investigation in the Fengshan River in Taiwan to survey the habitat distributions of the Japanese eel and Giant-mottled eel throughout a river. Moreover, we investigated whether their habitat distributions are related to their swimming and upstream migration. Thus, the mRNA expression levels of several candidate genes that may be associated with the swimming and upstream migration of eel were examined in the glass eels of the Japanese eel and Giant-mottled eel. Field investigation indicated that the Japanese eel mainly inhabited the lower and middle reaches of the Fengshan River, but the Giant- mottled eel was distributed over the middle to upper reaches. The mRNA expression levels of fMYH, dio2, gria3, and neurod1 were higher in the Giant-mottled eel than in the Japanese eel, implying that Giant- mottled eels might have better swimming bursts and more active upstream migration than Japanese eels. These results suggest that there is a habitat partition at which these two eel species coexist in a river, and their habitat distributions may be linked to their swimming bursts and upstream migration. Determining the habitat distributions of freshwater eels is important for developing applicable plans for eel conservation and resource management.

Preservative effect of carboxymethyl cellulose coating enriched with oregano (Origanum vulgare L.) essential oil on European eel (Anguilla anguilla) fillets during cold storage

Preservative effect of carboxymethyl cellulose coating enriched with oregano (Origanum vulgare L.) essential oil on European eel (Anguilla anguilla) fillets during cold storage

Trans-omics analyses revealed differences in hormonal and nutritional status between wild and cultured female Japanese eel (Anguilla japonica)

Long-term stock decline in the Japanese eel (Anguilla japonica) is a serious issue. To reduce natural resource utilization in Japan, artificial hormonal induction of maturation and fertilization in the Japanese eel has been intensively studied. Recent experiment on feminized (by feeding a commercial diet containing estradiol-17β for first half year) cultured female eels have shown ovulation problems, which is seldom observed in captured wild female eels. Therefore, the aim of this study is to try to investigate causes of ovulation problem frequently seen in cultured female eels by comparative trans-omics analyses. The omics data showed low growth hormone and luteinizing hormone transcription levels in the brain and low sex hormone–binding globulin transcription levels in the liver of the cultured female eels. In addition, it was found that high accumulation of glucose-6-phosphate and, maltose in the liver of the cultured female eel. It was also found that docosahexaenoic (DHA) acid, eicosapentaenoic acid (EPA) and arachidonic acid (ARA) ratios in cultured female eels were quite different from wild female eels. The data suggested that ovulation problem in cultured female eels was possibly resulted from prolonged intake of a high-carbohydrate diet and/or suboptimal DHA/EPA/ARA ratios in a diet.

Food risk characterization from exposure to persistent organic pollutants and metals contaminating eels from an Italian lake

ABSTRACTMonitoring environmental contaminants in edible animal species is important for the assessment of environmental quality and for food safety as well. In this study, the occurrence of 2,3,7,8 dioxins, and furans, dioxin-like polychlorinated biphenyls, six non-dioxin-like polychlorinated biphenyl indicators (ndl-PCBs), seven polybrominated diphenylethers (PBDEs), four polycyclic aromatic hydrocarbons (PAHs) and four metals (As, Hg, Ni, Pb) was evaluated in 90 European eels (Anguilla anguilla) from Lake Garda. The results on eel samples showed a frequent contamination of dl-PCBs, found at concentrations higher than the maximum limit (ML) provided by European Union in 41 % of the eels. Two PBDE congeners (BDE 47 and BDE 99) were detected in almost all the samples. The contamination by PAHs was found negligible; only one sample had a high concentration of benzo[a]pyrene. Concerning metals, Pb showed concentrations higher than the maximum level (ML) in 77% of the samples, while Ni content could be a cause of acute toxicity due to dermatitis. Extreme consumers (95th percentile) are subjected to an actual risk attributable to dioxins, furans, and mainly dl-PCBs and PBDEs. The contamination of Lake Garda eels is therefore a matter of concern and a constant monitoring of the pollution levels of its freshwater is mandatory.

The Comparison Extraction Methods of Crude Fat Content and Fatty Acid Profile of Eels (Anguilla marmorata (Q.) Gaimard) from Lake Poso

Eels (Anguilla marmorata (Q). Gaimard) from Lake Poso contain nutrition such as fatty acids EPA and DHA that are good for health. Extraction processes can be carried out to get the fats of these eels (Anguilla marmorata). This research aims to determine which one of the following extraction methods, namely: maceration and soxhletation, which is more appropriate to extract eels (Anguilla marmorata) so as to produce crude fats and the fatty acid profile with a higher content. The fatty acid profile was examined using the method of gas chromatography by converting results of the fat extraction into volatile fatty acid methyl esters. Research findings suggest that the obtained mean of crude fats was equal to 3.704% for the method of maceration and 28.872% for the method of soxhletation. Furthermore, results of the statistical testing analysis of the fatty acid profile generated a sig. a value greater than the 5% significance level, meaning that the content of fatty acids generated using the extraction method of maceration and that generated using the extraction method of soxhletation were not significantly different. This can be seen from the means of the fatty acid content, namely by 4.6956%, 9.6496%, and 1.5765% for the maceration method, and by 4.7287%, 9.338%, and 1.6646% for the soxhletation method. Based on the foregoing, it can be concluded that soxhletation is the appropriate extraction method.

Comparative Study of Fish Eel Amino Acid Profile (Anguilla marmorata (Q.) Gaimard) on Silver eel Phase from Palu River and Poso Lake

Amino acid is an organic component containing amine and carboxyl groups. Amino acids are needed by the human body. One animal that has the amino acid content is eel (Anguilla marmorata (Q.) Gaimard) from Palu River and Poso Lake in Central Sulawesi which are endemic fish. This study aims to determine the comparison of amino acid profile in eel (Anguilla marmorata (Q.) Gaimard) on silver eel phase. Testing amino acid profile using High Performance Liquid Chromatography (HPLC). The results showed that the eel (Anguilla marmorata (Q.) Gaimard) on phase of silver eel from the Palu River and Poso Lake contained 18 kinds of amino acid consisting of 9 kinds of essential amino acids and 9 types of non-essential amino acids. Data comparison shows a significant difference in glycine P = 0.000 and has no significant differences in the valine at P = 0.132.

Comparative Study on Fatty Acid Profile of Eel Fish (Anguilla bicolor) in Elver Eel and Silver Eel Phase from Palu River and Lake Poso

Eel (Anguilla bicolor) is a fish that has high enough nutrients such as fatty acids, vitamins and minerals. This study aims to determine the composition and fatty acid levels of eel (Anguilla bicolor) in the elver and silver eel phases from the Palu River and Lake Poso. The research sampling technique using purposive sampling method based on type, weight, size and place of collection and samples were analyzed using the Gas Chromatography tool to transform extracts the fat into fatty acid methyl esters. The results of the analysis of fatty acid types of eel fish (Anguilla bicolor) in elver eel phase from Palu river and Lake Poso were respectively, saturated fatty acids 6.085g/100g and 5.543g/100g, monounsaturated fatty acids 5, 157g/100g and 7, 817g/100g, polyunsaturated fatty acids 1, 265g/100g and 1, 950g/100g. Whereas in the silver eel phase respectively, saturated fatty acids 3, 829 g/100g and 4, 177g/100g, monounsaturated fatty acids 2, 035g/100g and 2, 859g/100g, polyunsaturated fatty acids 3, 370 g/100g and 0, 524g/100g. The results showed that the fatty acid levels of the eels fish in the elver and silver eel phases from Palu River and Lake Poso in the elver eel phase were significantly different, namely myristic acid, miristoleic acid, pentadecanoic acid, heptadecanoic acid, linoleic acid and linolenic acid, for. While the silver eel phase the sample taken from Palu River and Poso Lake were significantly different, namely, lauric acid, stearic acid, oleic acid and myristic acid.

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

ABSTRACTTwo 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.

Species Composition and Length-Weight Relationship of Anguillid Eels Habited in Bengkulu Waters, Indonesia

Management of euryhaline species, such as Anguillid eel, is very important. Anguillid eel is an important economic fish which the partly of its life cycle spent in inland waters then migrates into the ocean for spawning. The objective of this study is to identify the morphological diversity and length-weight relationship of Anguillid eels in this province. The total of 148 individuals of elver and adult Anguillid eels were caught was identified using the comparison of ano-dorsal with total length parameter. Cluster analysis was obtained based on measurement of morphometric parameter. The current work used cluster analysis and dendrogram to group the population characteristic of Anguilla eel. It revealed that in the Jenggalu, Kungkai and Manna rivers of Bengkulu province, there are two groups of Anguilla eel with significant difference of ano-dorsal length. The value of the ano-dorsal varied from 2.56 ± 1.54 and 17.78 ± 1.33 for A.bicolor bicolor and A.marmorata, respectively. The length-weight relationships between total length (TL) and weight (W) for Anguilla bicolor and A.marmorata were found to be highly significant (r2 &gt; 0.94, p &lt; 0.001). The average value of 'b' for length and weight were higher than 3, i.e., 3.2677 and 3.4821 in A.bicolor and A.marmorata respectively which indicated a positive allometric growth trend of this species in the studied area.

The influence of environmental cues on the activity of silver eels (Anguilla dieffenbachii) in Lake Manapouri, New Zealand

ABSTRACTLake Manapouri in the South Island of New Zealand has a significant hydroelectric generation facility, which potentially has a negative impact on the successful emigration of longfin eels (Anguilla dieffenbachii) from the upper Waiau catchment. Consequently, a trap-and-transfer programme has been implemented to allow silver (migratory) eels access to the sea. The present study analysed data on the timing of captures and numbers of silver eels over four seasons, including the influence of possible migration cues. Silver eels were captured over an extended season of seven months (November–May), with peak numbers during December and January. Flow at the lake outflow was found to have a weak relationship with the number of eels caught, as did lake level, but moon phase and rainfall had no significant effect. These results highlight the variability in silver longfin eel behaviour both in terms of timing and response to potential environmental cues.

Phylogenetic analysis of the complete mitochondrial genome of Anguilla japonica (Anguilliformes, Anguillidae)

The Japanese eel (Anguilla japonica), which was listed as Endangered (EN) under the International Union for the Conservation of Nature due to the declines in its abundance, overfishing, and its narrow range distribution. To better protect this species, we described the complete mitogenome of A. japonica in this study. The mitogenome is 16717bp in length and contains 13PCGs, two rRNA genes (12S rRNA and 16S rRNA), 22 tRNA genes, and a putative control region (CR) and one origin of replication on the light-strand (OL). Moreover, the 13 PCGs encode 3813 amino acids in total, all the protein-coding genes use the initiation codon ATG except COI uses GTG. Most of them have TAA or TAG as the stop codon, except COI uses AGG and two PCGs (COII and ND4) use an incomplete stop codon T. A phylogenetic tree based on the Neighbour Joining method was constructed to provide relationship within Anguilla, which could be a useful basis for conservation of this species.

어분대체 단백질원(대두박, 오징어간분, 콘글루텐밀) 첨가가 치어기 무태장어(Anguilla marmorata)성장과 어체 지방산과 아미노산 성분에 미치는 영향

어분대체 단백질원(대두박, 오징어간분, 콘글루텐밀) 첨가가 치어기 무태장어(Anguilla marmorata)성장과 어체 지방산과 아미노산 성분에 미치는 영향