Population structure of tropical eel (Anguilla bicolor bicolor) in Cikaso River, West Java

A. bicolor bicolor is a tropical eel subspecies that dominate catches in the coastal areas of West Java, and its conservation status is near threatened. Cikaso River, West Java, becomes eel migration path, while unfortunately, information concerning the stock of eel in this river is still inadequate. The objective of this study was to determine the population structure (size distribution, length-weight relationship, and condition factor) of A. bicolor bicolor in the Cikaso River. The research was carried out in the main streams of the Cikaso River and the coastal marsh of Ciroyom from January to December 2020. Eel samples were collected using lift-net, fishhook, and traps. The number of eels caught is counted, then the total length and weight are measured. We collected nine elvers and 89 yellow eels, but no silver eel was caught during the study. The elver's total length (TL) ranged from 10.2 to 20 cm, and the TL of yellow eel ranged from 20.1 to 42.2 cm. The catch of eel is dominated by the size of 25-30 cm. The growth pattern of eel in the Cikaso River is positive allometric, with the condition factor of eel ranging from 0.450 to 1.917 (1.160±0.3096).

Temporal, spatial, and biological variation of nematode epidemiology in American eels

American eels (Anguilla rostrata) are infected by the non-native parasitic nematode Anguillicoloides crassus, which can cause severe swim bladder damage. We investigated epidemiology of A. crassus to better understand its population-level effects on American eels. Nematode prevalence, abundance, and intensity and swim bladder damage were quantified in glass eels, elvers, and yellow eels from the lower Chesapeake Bay and related to season of capture, river system, and total length. Age-variant force-of-infection and disease-associated mortality were estimated using a three-state irreversible disease model, which assumes recovery is not possible. Results showed glass eels have very low infection prevalence and severity compared with elvers and yellow eels. Nematode abundance varied by season, river, and eel length, whereas swim bladder damage varied by season and eel length. Nematode abundance and swim bladder damage were weakly positively correlated. Force-of-infection, based on swim bladder damage, peaked at age 2, and disease-positive eels had an estimated lower annual survival probability of 0.76 compared with disease-negative eels. Full understanding of American eel population dynamics will require broader knowledge of cryptic disease-associated mortality throughout North America.

Identification and Prevalence of Parasites Isolated from Eels (Anguilla bicolor) Along Migrated Pathway at Serayu River, Central Java

Eels especially Anguilla bicolor has been a major capture species along the migration pathways at Serayu river for both consumption and aquaculture purposes. Yellow eels always exhibited a strong and health when they were caught. However, mass mortalities always found during holding and culture period. Parasites was one of the obstacles of the eels aquaculture. The aims of this study were to observed the health status and parasites investation of eels along the migration pathway. Three capture stations namely Adipala, Sampang and Purwojati were appointed as a sampling sites. Thirty captured eels ranging from 25.48 cm – 28.92 cm were randomly selected at each sites during October to December 2018.Ninety eel samples demonstrated in a good health. Ectoparasites observation discovered that Trichodina was the predominant parasites. Further indentification revealed that they were belongs to T. matsu, T. domerguei and T. jandarica with prevalence rate ranged from 40% to 90%. Whilst Vorticella found at low prevalence and intensity namely; 6.7% and 0.2 respectively. The endoparasites nematodes obtained were Anguillicola and Spirocamallanus with prevalence rate and intensity 3.3%-6.7%, 0.03 – 0.06 and 13.3%, 0.13 respectively. Molecular identification of nematodes demonstrated that they were closely related to Anguillicola crassus and Spirocamallanus philppinensis with similarity 95.40% and 97.93% respectively. There were no genetically differences between two species Anguillicola crassus from Adipala and Sampang. From this study it can be seen that Eels migrated upstream were in a good heatlh. Trichodina, Vorticella, Anguillicola and Spirocamallanus found infestated eels during upstream migration.

Early back-calculated size-at-age of Atlantic yellow eels sampled along ecological gradients in the Gironde and St. Lawrence hydrographical systems

An international sampling program investigating the causes of the decline of American eels (Anguilla rostrata) and European eels (Anguilla anguilla) in the St. Lawrence (Canada) and Gironde (France) rivers systems provided the opportunity to compare early growth of eels of each species among habitats using back-calculated size-at-age from 1 to 5 years old. Our study supports previous studies showing that the early back-calculated lengths of A. anguilla were higher in downstream and more saline Gironde system habitats than in the upstream fluvial section and provides a new indication that length at 1 year old is twice higher than that reported 10 years earlier. However, our data contradict the current paradigm for A. rostrata by providing evidence that early size-at-age of eels from the upstream St. Lawrence system, most distant from the spawning area, exceeds those of eels sampled downstream, at less distant sites in the estuarine section. Overall, these observations are consistent with the hypothesis that the observed spatial variations in early growth rate of yellow eels sampled in the St. Lawrence and Gironde systems are the consequence of processes occurring in the first year of age, such as genetic selection and (or) genetically dependent habitat choice.

Organic and inorganic contamination impacts on metabolic capacities in American and European yellow eels

American (Anguilla rostrata) and European (Anguilla anguilla) eel populations are declining since the 1980s, and contamination is thought to play a role. To determine the influence of organic (organochlorinated pesticides (OCPs), polybrominated diphenyl ethers (PBDEs), polychlorinated biphenyls (PCBs)) and inorganic (Zn, As, Cd, Cu, Pb, Cr, Ni, Ag, Se, Hg) contaminants on wild yellow eels liver and muscle metabolic capacities, enzymatic assays were performed. In A. rostrata liver, G6PDH moderate negative correlations with Ag, Pb, and As suggest impacts on lipid metabolism, and correlations between Cd and age (positive) and between Cd and relative condition factor (Kn; negative) indicate impacts on older eels health. Anguilla anguilla liver proteins, pyruvate kinase (PK), and lactate dehydrogenase (LDH) were positively linked to Zn, Pb, and Cu, suggesting effects on glycolytic and anaerobic capacities. In A. anguilla muscle, absence of correlation between age and lipids plus strong positive correlations between age and OCPs, PBDEs, PCBs, and Hg suggest lipid storage impairment in older contaminated eels. Overall, our study indicates contamination impacts on both species’ metabolic capacities, but the broader range of contaminants found in A. anguilla brings greater impacts compared with A. rostrata.

CURRENT STATUS AND PROBLEMS OF THE CATCH STATISTICS ON ANGUILLID EEL FISHERY IN INDONESIA

To compensate the decline of the populations of temperate anguillid eels, tropical anguillid eels become getting attention of East Asian eel market in recent years. Many eel farms have been established in Java Island to culture tropical anguillid eels intending to export the products to East Asia. Since eel farming is reliant on wild-caught anguillid eels such as glass eels, elvers and yellow eels, these eel seeds have been captured in various places in Indonesia. However, it is still unknown that how much of tropical anguillid eels are caught as seeds for eel farming. This study showed two different patterns of the commodity chains of eel seeds from both Sukabumi Regency and Bengkulu Province to the eel farms in Java Island. Official catch statistics on anguillid eels found in both Sukabumi Regency and Bengkulu Province were also analyzed on their features and problems underlied. Considering the sustainable use of anguillid eel resources and critical stances on exploitation of eel seeds from all over the world, the Indonesian government should take an immediate action for developing the national catch statistics on anguillid eel fishery as soon as possible.

Eel visual pigments revisited: The fate of retinal cones during metamorphosis

During their complex life history, anguilliform eels go through a major metamorphosis when developing from a fresh water yellow eel into a deep-sea silver eel. In addition to major changes in body morphology, the visual system also adapts from a fresh water teleost duplex retina with rods and cones, to a specialized deep-sea retina containing only rods. The history of the rods is well documented with an initial switch from a porphyropsin to a rhodopsin (P5232 to P5011) and then a total change in gene expression with the down regulation of a “freshwater” opsin and its concomitant replacement by the expression of a typical “deep-sea” opsin (P5011 to P4821). Yellow eels possess only two spectral classes of single cones, one sensitive in the green presumably expressing an RH2 opsin gene and the second sensitive in the blue expressing an SWS2 opsin gene. In immature glass eels, entering into rivers from the sea, the cones contain mixtures of rhodopsins and porphyropsins, whereas the fully freshwater yellow eels have cone pigments that are almost pure porphyropsins with peak sensitivities at about 540–545 nm and 435–440 nm, respectively. However, during the early stages of metamorphosis, the pigments switch to rhodopsins with the maximum sensitivity of the “green”-sensitive cone shifting to about 525 nm, somewhat paralleling, but preceding the change in rods. During metamorphosis, the cones are almost completely lost.