Mottled Eel Research Articles

Feed supplementation with quorum quenching probiotics improved growth response, immune response, and resistance in the giant mottled eel, Anguilla marmorata

This study aimed to evaluate the effect of feed supplementation with quorum quenching (QQ) probiotic bacteria on growth performance, hematology, immune response, and disease resistance in giant mottled eels. The feed used was supplemented with 45 ± 2.3 g/individual QQ bacteria using the following treatments, namely Bacillus cereus strain B8, Pseudomonas putida strain BPA1, Bacillus cereus strain HPC 576, and control (no QQ). A total of 420 eels (average weight 45 ± 2.3 g/ind.) were randomly reared in 12 open tarpaulin ponds of 2 x 1 x 1 (W x L x D) m and 1000-L volume for 8 weeks. Feed was given three times per day at 5% of the body weight. Water was changed daily at 25%, and shelters were provided using 3-inch diameter PVC pipes. The results showed that the feed containing QQ bacteria improved the growth, hematology, immunity, and disease resistance of the eels compared to the control (P < 0.05). Furthermore, among the QQ bacteria tested, the feed with B. cereus strain HPC 576 had the highest performance in all tested parameters.

High spatial variability in a species-rich assemblage of diadromous fishes in Hong Kong, southern China.

China has experienced substantial coastal reclamation and damming of rivers. These changes have the potential to impact migrations of diadromous fishes between the sea and fresh waters, but the composition of these fishes and the impacts of barriers to their movement in China have received little attention. We inventoried the species composition and distribution of diadromous fishes, and the impacts of barriers on them, in the Hong Kong Special Administrative Region (HKSAR), southern China. Fish assemblages were surveyed using hand-nets, supplemented by cast-netting and single-pass snorkel surveys, in 24 small coastal streams across three regions. Surveys were undertaken on multiple occasions during the wet and dry seasons to account for the monsoonal tropical climate. Twenty-eight diadromous fishes were collected, mostly gobies, amounting to over half (53%) of the total richness of primary freshwater fishes; four additional species are known from literature records. Diadromous richness was 48% greater during the wet season, when all species were encountered. Richness varied substantially among streams, from a maximum of 17 (2 streams that were diversity hot spots) to none (3 streams). The most widespread diadromous fish was Glossogobius giuris (71% frequency of occurrence), followed by Mugil cephalus (58% occurrence) and Eleotris oxycephala (50% occurrence). The remaining 25 diadromous fishes occurred in fewer than half of the streams; 12 species were confined to a single stream and may be locally threatened. There were conspicuous spatial differences in diadromous assemblages across HKSAR, despite its limited extent (1114 km2), the proximity of the surveyed streams, and the broad geographic distribution of most species. Regional species assemblages were influenced by localized habitat characteristics, with a noticeable distinction between areas with and without large, fast-flowing, and highly oxygenated streams. The presence of in-stream barriers (weirs: 0.3-8.7 m high) did not affect spatial patterns in species assemblages, although, on average, diadromous richness was lower in weir-obstructed streams (4.0 vs. 6.9 species in unobstructed streams). In total, 18 species were confined to unobstructed streams or sections below weirs, whereas the remaining 10 species were recorded both above and below weirs. Only the mottled eel (Anguilla marmorata) and a goby (Stiphodon multisquamus) were able to ascend weirs over 2 m. Although at least 400 m of the lower course of each stream was sampled, diadromous fishes were confined to the first 300 m in 12 of the 13 weir-obstructed streams. Remarkably, the tally of 32 diadromous species in HKSAR exceeds the 19 known from mainland China, highlighting the need for further research on composition and conservation status of diadromous fishes.

Environmental DNA Reveals Geographic Distributions of Two eel Species, Anguilla japonica and A. marmorata, in Western Kyushu, Japan.

Some anguillid eels migrate thousands of kilometers from their spawning grounds, dispersing across vast geographic areas to fresh and brackish water habitats, where they settle and grow. Japanese eels (Anguilla japonica) and giant mottled eels (A. marmorata) are both found in Japan, although their distributions differ, and their exact distributions are poorly known. We assumed that topographic distribution patterns of Japanese and giant mottled eels must differ among and within rivers along the northwest coast of Kyushu, Japan. Environmental DNA (eDNA) analysis was conducted at 87 sites in 23 rivers. Japanese eel eDNA was detected in 19 rivers (82.6%) and that of giant mottled eels was detected in eight (34.8%). We detected giant mottled eel eDNA in five rivers where they were previously unknown. eDNA for Japanese eels was detected at six of nine sites in the north (66.7%), 13 of 23 sites in Omura (56.5%), and 37 of 55 sites in the south (67.3%). In contrast, giant mottled eel eDNA was detected at one of nine sites in the north (11.1%), no sites in Omura, and 15 of 55 sites in the south (27.3%). There was no correlation between eDNA concentrations of the two species at 10 sites in the five rivers where eDNA of both species was detected. These findings suggest differences in the distribution of the two eel species and the northern distributional limit of giant mottled eels in the area facing the East China Sea.

Effects of adding spermidine carbon quantum dots in feed on growth, intestinal morphology, immunity and disease resistance of Anguilla japonica and Anguilla marmorata

Japanese eel (Anguilla japonica) and giant mottled eel (Anguilla marmorata) are the main eel species reared in recirculating aquaculture system (RAS) in Taiwan. RAS increases the rearing density of eel. On the other hand, it spreads pathogens and diseases more efficiently and uncontrollably. Currently, eel farmers use antibiotics to control disease in RAS, but their misuse can lead to resistance and food-safety issues. Spermidine carbon quantum dots (CQDSpds), a newly developed carbon nanomaterial with positive charges on the surface, can bind to the negatively charged bacterial cell membrane to destroy bacteria and not cause drug resistance. This research investigated the effects of different concentrations of CQDSpds as paste feed additives on the growth performance, intestinal morphology, immune-related gene expression, and disease resistance of Japanese and giant marble eels. The results showed the highest final body weight, weight gain, and specific growth rate of Japanese eel and giant mottled eel fed with 1 ppm and 0.5 ppm CQDSpds added. Compared with the control group, 1 ppm CQDSpds group showed higher lysozyme expression in Japanese eels. In the part of intestinal morphology, there was not a significant difference in intestinal villus height and intestinal morphology between the CQDSpds groups and the control group in both eel species. The survival rate of each group supplemented with CQDSpds was higher than the control group after the E. tarda challenge test, among which the highest were found at 1 ppm group in Japanese eel and 0.5 ppm group in giant mottled eel. By this research, the additive of CQDSpds in eel culturing could improve the growth and immune performance with not caused an impact on the intestine of both eels, which can be a potential feed additive in intensive eel farming.

Validating the occurrence of the giant mottled eel (Anguilla marmorata) in the Galápagos Islands.

The giant mottled eel (Anguilla marmorata) is distributed mostly in the Indo-West Pacific. However, a few records indicate the presence of this eel in the Tropical Central and East Pacific. In April 2019, an eel specimen was caught in a small stream in San Cristobal Island, Galápagos. Morphological and molecular characters (16S and Cytb mtDNA sequences) confirmed the species as A. marmorata Quoy & Gaimard, 1824. The re-discovery of A. marmorata in Galápagos supports the hypothesis of an eastward range expansion from the west, probably through the North Equatorial Counter-Current.

Economic Impact of the Eel. Eel (Anguilla Bicolor) Aquaculture on Local Communities in Banyuwangi Regency

Aquaculture in Indonesia has several superior commodities, one of which is eel. Eel (Anguilla bicolor) is a fish with high economic value and a type of fish that is an export commodity (Japan, Hong Kong, Germany, Italy, and several other countries). This condition is inversely proportional to the level of domestic eel consumption which is still relatively low. Aquaculture activities provide direct and indirect impacts on the local society, one of them is the economic impact of the existence of giant mottled eel aquaculture in the Banyuwangi District. The research aimed to analyze the economic impact of giant mottled eel aquaculture activities. The Survey research method was used and data were analyzed using descriptive and multiplier effect analysis. The research result of the economic impacts of giant mottled eel aquaculture that provides a positive economic impact on local society is indicated by the development of giant mottled eel aquaculture activities and the other sectors. Keynesian Local Income Multiplier value was 2.65. Type I Multiplier Income Ratio was 1.16 and Type II Multiplier Income Ratio was 1.6.

Effects of Different LED Light Spectra on Growth and Immunity of the Japanese Eel (Anguilla japonica) and Giant Mottled Eel (A. marmorata).

Indoor recirculating aquaculture systems make light control possible and enable the usage of specific coloured lights to promote the growth and immunity of aquaculture species. Five different LED wavelengths (white light [460 nm], red light [622 nm], green light [517 nm], blue light [467 nm], and the dark) were used in this study to evaluate growth and immunity in the glass eel stage of two high-valued anguillid species, Japanese eel (Anguilla japonica) and giant mottled eel (A. marmorata). There were no significant differences in growth of the Japanese eel among the groups after 12 weeks of feeding (p > 0.05); the survival rate of each group was over 95%. The giant mottled eel showed better growth in total length and body weight in the red light and dark groups (p < 0.05). Expression levels of immune-related genes were not significantly different between each group of the Japanese eel and the giant mottled eel (p > 0.05). The growth of the Japanese glass eel was not significantly sensitive to different LED wavelengths, while the giant mottled glass eel showed better growth under red light and dark environments. Neither eel species showed significant differences in innate immunity under different LED wavelengths.

Contrasting riverine distribution and habitat use of the Japanese eel, Anguilla japonica, and the giant mottled eel, Anguilla marmorata, in a sympatric river.

Electrofishing and visual observations revealed contrasting riverine distribution and habitat use of the Japanese eel, Anguilla japonica, and the giant mottled eel, Anguilla marmorata, in a relatively gentle-slope river of Southern Kyushu, Japan. A. japonica was distributed in the lower and upper reaches. A. marmorata inhabited the middle reaches with relatively fast water velocity, heterogeneous water depth, coarse substrata and no adjacent paddy fields. This may have important conservation implications because a decrease in environmental diversity and/or river connectivity could result in the disappearance of A. marmorata habitats.

Genetic Diversity and Population Structure of the Giant Mottled Eel, Anguilla marmorata Quoy &amp; Gaimard, 1824 in Central Vietnam

The giant mottled eel, Anguilla marmorata, is at high risk of extinction due to overfishing of glass eels and elvers to provide stock for eel farming. In Vietnam, information on the genetic diversity and population structure of this species, which is necessary for resource management, is limited. In order to address this paucity of information, sequencing of the entire mitochondrial control region (mtDNA) was carried out for 176 individuals collected from central Vietnam. The sequences were investigated using various genetic, phylogenetic and population analyses. A total of 165 distinct haplotypes were identified. The percentage of variation within and among populations was 99.26% and 0.74%, respectively. The fixation index was low (0.007) and not significant (p = 0.096). Therefore, panmixia and a lack of significant population genetic structuring seem likely for A. marmorata in central Vietnam. Most sampled eels were genetically similar to eels found in North Pacific populations (Japan, Taiwan and the Philippines), except for one sample from Quang Tri and two samples from Binh Dinh, which had high values of genetic identity (97% to 99%) with South Pacific populations (Tahiti, Fiji, New Caledonia and Papua New Guinea). Taken together, we suggest that A. marmorata from the North and South Pacific populations co-exist in central Vietnam.

Correlation the Distance of the Location Found With the Size and Dominant Index of Eel in East Nusa Tenggara Waters

The existence of eels in a freshwater area is influenced by various factors, one of which is the availability of habitats that are suitable for the life of eels. East Nusa Tenggara Province is an archipelago that is mentioned as one of the distribution areas for eel in Indonesia. However, the type and size of eel is strongly influenced by the distance it finds. The farther the river is from the estuary, the larger the size of the eel and the different types. As eurihaline migratory fish, eels can swim far upstream to find a suitable habitat for their life. This study aims to analyze the relationship between location distance and the size and dominance index of eel in freshwater in East Nusa Tenggara (NTT). This research was conducted from October to April. The results obtained are that the three rivers in East Nusa Tenggara province, namely the Tarus river in Kupang district, the Oetona river in Kupang city and the Kamaifui river in Alor district, managed to catch 71 eels at a fishing distance of 0.69 km to 7.86 km. from the mouth of the river. Based on the ano-dorsal analysis, two types of eel caught in the Tarus and Kamaifui rivers were identified, namely Anguilla marmorata and Anguilla nebulosa nebulosa, while in the Oetona river only A. marmorata was found. Based on the calculation of the dominance index, the most dominant species in fresh waters of NTT is A. marmorata.

Residence, activity patterns and behaviour of the giant mottled eel Anguilla marmorata in two freshwater protected areas in the Philippines

Abstract Despite the giant mottled eel Anguilla marmorata being a widely distributed and locally exploited species throughout the Indo Pacific region, understanding of its life history, behaviour and movement ecology remains limited. Knowledge of animal spatial ecology is essential for the effective design and siting of aquatic protected areas. In the current study, acoustic telemetry was used to quantify residence and explore the activity patterns and behaviour of A. marmorata (n = 68) in two freshwater protected areas (FPAs) for the first time in the Cagayan River Basin, Philippines. The results demonstrated that FPAs of only 1 km length provided refuge for A. marmorata for an average of 25–26% of the tracked period. Residence and activity patterns varied with habitat type. In pool and riffle habitat, activity reduced with increased river flow, and eel, particularly larger individuals, were more strongly nocturnal than those in the deep pooled, slow flowing habitat. Typhoon events displaced many individuals, particularly in the pool and riffle habitat, with only 3% returning to the FPA within the study. Findings are discussed within the context of selecting FPA sites to optimize eel protection within catchments experiencing high non‐selective fisheries exploitation and other threats.

Morphological and gonadal histological characteristics of the silver-phase male Indo-Pacific eel Anguilla marmorata.

Eight silver-phase male Indo-Pacific eels (giant mottled eels) Anguilla marmorata were collected from three small rivers on subtropical Amami-Oshima Island, Japan, and their morphological and gonadal-histological characteristics were examined. The total length, body mass and age of the silver eels were 543.8 ± 49.3 (496-659)mm, 376.0 ± 116.0 (282-660)g and 14.6 ± 2.3 (11-19)years old, respectively. The silvering-related characteristics (eye index, pectoral-fin index, gut-somatic index) and reproductive characteristics (gonadosomatic index, histological stage) of the silver eels were significantly advanced compared to those of yellow eels, which is similar to other anguillid species.

Fish Species Composition and Distribution from 2015 to 2019 in the Ibulao River, Ifugao, Cordillera, Philippines

The composition, diversity, and distribution of fish species in the Ibulao River were surveyed from January to December 2015-2019. The samples for fish species identification were collected from the landed catch of three landing centers in the Ibulao River, namely: Lamut, Kiangan, and Lagawe in the Province of Ifugao, Philippines. The sampling of stocks was conducted using the National Stock Assessment Program (NSAP) methodology. A total of 18 fish species from 11 families were recorded. The river supports four endemic species, two native species, 11 introduced species, and one species for further identification. The status of one goby species will be determined upon identification at the species level. In 2015 and 2016, the most dominant catch in the Ibulao River was Cyprinus carpio (common carp), but from 2017 to 2019, the most dominant catch was Oreochromis niloticus (Nile tilapia). These two introduced fish species constituted the top 2 fish species in the Ibulao River from 2015 to 2019. The native fish species, which are the migratory fish Anguilla marmorata (giant mottled eel) and the Awaous melanocephalus (largesnout goby), are found in all the landing centers but with an observed declining catch. This information will serve as a basis for formulating protection and conservation policies for the fish species and their habitat in the Ibulao River.

Phylogenetic analysis and characterization of a new parasitic cnidarian (Myxosporea: Myxobolidae) parasitizing skin of the giant mottled eel from the Solomon Islands.

Myxosporeans are microscopic cnidarians associated with severe diseases in aquaculture and wild fish populations. This group of parasitic cnidarians thus warrants close attention concerning its potential impact on susceptible fish stocks. At present, little is known about this group of parasites infecting anguillid eels. From myxospore specimens collected from a freshwater eel (Anguilla marmorata) in the Solomon Islands, we describe a new species belonging to the genus Myxobolus based on an integrative taxonomic analysis of morphological, biological traits and molecular data. Furthermore, we determined the phylogenetic position and relationships of this species among other platysporine myxosporeans. Molecular phylogenetic assessment of small subunit ribosomal DNA showed that the species clusters together with Myxobolus portucalensis and Echinactinomyxon type 5 Özer, Wootten and Shinn, 2002, in a well-supported subclade. This is the first report of a myxosporean parasite infecting fish from the Solomon Islands.

Colour vision in the tropical giant mottled eel Anguilla marmorata as determined by classical conditioning test

The giant mottled eel Anguilla marmorata Quoy & Gaimard is an important aquaculture candidate in eel farming industry. The high economic value of the species leads to intensive cultivation affecting its welfare under farm condition. Since colour environment affects the welfare of confined fishes, basic information on colour vision is necessary. By means of a behavioural experiment of A. marmorata elvers in the laboratory, we determined colour vision under natural daylight. The elvers were subjected to classical conditioning to associate a reward feed with a blue or a green stimulus placed amid seven shades of grey. The elvers learned this visual task after 30 or 36 trials and thus the ability of colour discrimination was confirmed. Since the elvers have the retinal tapetum, it may be suggested that colour vision in dim light enables crepuscular feeding by the A. marmorata elvers, clearly an advantage in aquaculture.

First detection of Herpesvirus anguillae (AngHV-1) associated with mortalities in farmed giant mottled eel (Anguilla marmorata) in Vietnam.

Giant mottled eel (Anguilla marmorata) farming in Vietnam is a multistage process starting from wild harvest of glass eels through the so-called "hatcheries" and distribution centres from which individuals are transferred to rearing farms and subsequently sold by one eel farm to another every 3-5months. The information on viral agents spread and persistence in the Vietnamese eel aquaculture is scarce. Therefore, the mortality of A. marmorata at the Van Xuan Farm was the prerequisite to identify the possible aetiologic agent and additionally to formulate first recommendations for viral disease screening in the Vietnamese eel aquaculture. Juvenile giant mottled eels with haemorrhagic lesions in the skin and liver, and hyperaemia of the gut were tested with qPCR and end-point PCR for AngHV-1 presence. Here, we report the first detection of AngHV-1 associated with mortality in giant mottled eel in winter and spring seasons. On the basis of the obtained results, we recommend to test eel seeds in "hatcheries," since tropical eel farms operate in interconnected scheme and monitoring of AngHV-1 prevalence requires well-implemented measures. Disease screening in the rearing centres and on-growing facilities should be based on everyday health checks, including by-catch fish used as a base of the feeding programmes at eel farms in Vietnam.

Pseudodactylogyrus anguillae (Yin & Sproston, 1948) from the giant mottled eel Anguilla marmorata Quoy & Gaimard, 1824, in the Phongolo River, South Africa: an invader on the African continent.

The global invasive anguillid gill parasite Pseudodactylogyrus anguillae (Yin and Sproston, 1948) has only recently been documented from eels in South Africa. As there is no known eel trade in South Africa, the source of introduction of this parasite has been debated, and its status as an alien parasite was rendered uncertain. We report on the first infection of Pseudodactylogyrus anguillae from the giant mottled eel Anguilla marmorata from the Phongolo River (South Africa) using classic morphological and molecular methodologies and clarify the introduction status category of this parasite as alien and invasive.

First record of cannibalism in the giant mottled eel Anguilla marmorata (Actinopterygii: Anguilliformes) as revealed by DNA barcoding

First record of cannibalism in the giant mottled eel Anguilla marmorata (Actinopterygii: Anguilliformes) as revealed by DNA barcoding

An overview of the Anguillid eel culture in Vietnam

The wild eel fishery and eel farming are playing an increasingly important role in aquaculture. Most of the Anguillid eel fries at their glass eel stage are caught in the two provinces of Vietnam, viz., Phu Yen and Binh Dinh, which accounts for over 80% and 10-15%, respectively. The stages of raising eels in Vietnam are very diverse with the survival rate of Anguilla Marmorata is approx. 60% through glass eel and elver stages. The major eel grow-out area of Vietnam is in Mekong delta. Ca Mau province is the highest in eel farming among the 14 provinces in the country. There are over 1,000 eel farms produced about 2,000–5,000 tons of eel in Vietnam at this moment. Around 95% of the total number of farms produced giant mottled eel (A. marmorata), and most of the production (70%) was used for domestic consumption, while30% was exported to the adjacent countries.

Habitat preference, movements and growth of giant mottled eels, Anguilla marmorata, in a small subtropical Amami-Oshima Island river.

Although anguillid eel populations have decreased remarkably in recent decades, few detailed ecological studies have been conducted on tropical eels such as the giant mottled eel whose range extends across the whole Indo-Pacific. This species was studied throughout the entire 0.5 km mainstem reaches of Oganeku River on the subtropical Amami-Oshima Island of Japan over a two-year period using four sampling periods to understand its habitat preference, early life-stage dispersal process, movements, and annual growth using a mark-recapture experiment conducted with quantitative electrofishing. A total of 396 juvenile growth-phase A. marmorata eels were caught and tagged, with 48 individuals being recaptured at least once. Their density irrespective of size of eels was most strongly determined by distance from the river mouth, followed by riverbank type according to random forest models. Eel density decreased with increasing distance from the freshwater tidal limit located about 100–150 m from the river mouth. Eels preferred vegetated riverbanks, while they avoided those of concrete and sand. The density of small eels (total length: TL < 240 mm) was also associated with depth and velocity, with small eels tending to prefer riffle or run habitats. In contrast, large eels (TL ≥ 240 mm) were found in habitats of any depth and velocity. The TL of eels had a minimum peak at around the tidal limit, and it increased with increasing distance from the tidal limit. The observed density and size gradients of eels in relation to the distance from the river mouth suggested that A. marmorata initially recruited to freshwater tidal limit areas and then dispersed in both downstream and upstream directions. The growth rate of eels varied greatly among individuals that were at large for various periods of time and ranged from 0 to 163.2 mm/year (mean ± SD of 31.8 ± 31.0 mm/year). Of the recaptured eels, 52.1% were recaptured in a section that was different from the original capture section, and their mean ± SD distance travelled was 46.5 ± 72.5 m (median = 20 m). 47.9% of the eels were recaptured from the original section of capture (i.e., <10 m distances travelled), suggesting that they had strong fidelity to specific habitats with limited movements. The distance travelled of eels that had moved was greater for small eels (range = 10–380 m; mean ± SD = 84.4 ± 121.9 m) than large individuals (range = 10–120 m; mean ± SD = 30.9 ± 31.0 m), which indicates that the mobility of the eels declines as they grow. This is the first clear detailed documentation of the spatial distribution, growth, and movements of tropical eels in a small river system in relation to environmental conditions that provides an example of how future studies can be conducted in other areas to understand how conservation efforts can be most efficiently targeted for maximum success.