Tropical Eel Anguilla Marmorata Research Articles

Genomic signatures for latitudinal selection in the tropical eel Anguilla marmorata.

Selection acting across environmental gradients, such as latitudes, can cause spatial structuring of genomic variants even within panmictic populations. In this study, we focused on the within-generation latitudinal selection between northernmost and southernmost individuals of the North Pacific population of a tropical eel Anguilla marmorata, which shares its northernmost distribution with a temperate eel Anguilla japonica. Whole-genome sequencing data indicated that the northernmost and southernmost individuals of A.marmorata belong to a single panmictic population, as suggested by previous studies. On the contrary, parts of genomic regions across multiple chromosomes exhibited significant genetic differentiation between the northernmost and southernmost individuals, and in these genomic regions, the genotypes of the northernmost individuals were similar to those of A.japonica. These findings suggested within-generation latitudinal selection of A.marmorata, which might have led to genetic closeness between northernmost A.marmorata and A.japonica.

Optimum Salinity for Growth of Tropical Eel Anguilla marmorata Quoy & Gaimard, 1824 in Nursery Culture

Optimum Salinity for Growth of Tropical Eel Anguilla marmorata Quoy & Gaimard, 1824 in Nursery Culture

Differential expression of skin mucus C-type lectin in two freshwater eel species, Anguilla marmorata and Anguilla japonica

Two types of lactose-specific lectins, galectin (AJL-1) and C-type lectin (AJL-2), were previously identified in the mucus of adult Anguilla japonica. Here, we compared the expression profiles of these two homologous lectins at the adult and juvenile stages between the tropical eel Anguilla marmorata and the temperate eel A. japonica. Only one lectin, predicted to be an orthologue of AJL-1 by LC-MS/MS, was detected in the mucus of adult A. marmorata. We also found that an orthologous gene to AJL-2 was expressed at very low levels, or not at all, in the skin of adult A. marmorata. However, we detected the gene expression of an AJL-2-orthologue in the skin of juvenile A. marmorata, and a specific antibody also detected the lectin in the juvenile fish epidermis. These findings suggest that expression profiles of mucosal lectins vary during development as well as between species in the Anguilla genus.

Effects of metamorphosis timing and the larval growth rate on the latitudinal distribution of sympatric freshwater eels, Anguilla japonica and A. marmorata, in the western North Pacific

Abstract Background Early life history traits of the temperate eel Anguilla japonica and tropical eel Anguilla marmorata were examined to determine the possible reason why these two species have similar spawning areas and oceanic larval transport in the North Equatorial Current and yet are recruited to different but partly overlapping continental growth habitats in northern East Asia. To understand the segregative migration of these two sympatric eel species, their glass eels were collected from nine estuaries in the Philippines, Taiwan, Japan, and China. The age at metamorphosis from leptocephalus to glass eel (T m), the age at estuarine arrival (T t), the time between metamorphosis and estuarine arrival (T t−m), and the growth rate (G t) of glass eels were calculated from daily growth increments in their otoliths. Results Results indicated that the G t was faster and the T m was younger in A. marmorata than in A. japonica. On the other hand, fish length and the T t at estuarine arrival were larger in A. japonica than in A. marmorata, indicating that elvers of A. japonica experience a longer oceanic drift than those of A. marmorata. In addition, the T t−m also indicated that A. japonica experienced a longer coastal migration than A. marmorata. Conclusion This study validated that the T m and G t seem to play important roles in the segregative migration and latitudinal distribution of these two sympatric freshwater eel species in the northwestern Pacific.

Heavy Metals in a Tropical Eel Anguilla marmorata from The Central Part of Vietnam

In order to understand the present status of heavy metal contamination and the risk associated with human consumption, commercial freshwater eels in Vietnam were examined. The concentration of eight elements (Cr, Mn, Co, Cu, Zn, Sr, Cd, and Pb) was determined in muscle tissue of tropical eel Anguilla marmorata collected in four provinces, Quang Tri, Quang Ngai, Binh Dinh, and Phu Yen, from the central part of Vietnam. Concentrations of Cu, Zn, Cd, and Sr were found to be highest, whereas Co concentration showed the lowest at Quang Tri. Cr was recorded to be lowest in Quang Ngai, while the amounts of Mn and Pb did not vary among locations. Although the metal concentrations in the muscle of A. marmorata did not represent a risk for human consumption, elevated Cd concentrations in Quang Tri related to agriculture activities suggest that further investigations should be undertaken to clarify the potential risk to the eel population.

Disparities in habitat use and migratory behavior between tropical eel Anguilla marmorata and temperate eel A. japonica in four Taiwanese rivers

Strontium (Sr):calcium (Ca) ratios in otoliths of the eels Anguilla japonica and A. mar- morata caught in 4 Taiwanese rivers were examined to reconstruct their migratory environmental history. In all sampling locations, each eel species preferred a different environment and all were dif- ferently distributed in the river. A. japonica was more abundant than A. marmorata in the lower reach, accounting for 76 to 86% of the eel population. In contrast, A. marmorata was more abundant than A. japonica in the upper reach, accounting for 76 to 100% of the eel population. A. japonica con- sisted of diversified migratory contingents, including freshwater, brackish-water and seawater eels, but A. marmorata tended to reside in freshwater and seemed to avoid seawater during the yellow eel stage. This disparity in migratory behaviors and habitat use between species may reflect interspecific competition and adaptive radiation. The flexible migratory behavior and adaptation to different salinities of A. japonica may be an advantageous evolutional fitness when facing competition, heavy fishing pressure and environmental stress. The freshwater-restricted A. marmorata is more easily threatened by both fishing pressure and continuous habitat degradation than A. japonica.

Evidence of a spawning area of Anguilla marmorata in the western North Pacific

Leptocephali of the tropical eel Anguilla marmorata have been consistently collected in the same area of the North Equatorial Current (NEC) in the western North Pacific during three consecutive cruises in June and July of 1991 (N=28) and 1994 (N=20), and July and September of 1995 (N=27), indicating that this is a spawning area of this species. These leptocephali were collected from 130°E to 142°E and 12°N to 20°N, to the west of the Mariana Islands, in 20 tows in 1991, in 13 tows in 1994 and in 17 tows in 1995, indicating a widespread presence, but a relatively low abundance. Six of these specimens (16.3–36.0 mm total length) from the 1995 cruise, which were of the typical size range of these leptocephali, were genetically confirmed to be A. marmorata in a previous study. The consistent presence of recently spawned A. marmorata leptocephali (9–20 mm) in all 3 years, suggests that the western region of the NEC is the spawning area of the northern population of A. marmorata that was identified in a recent population genetics study. These leptocephali would thus be transported westward by the NEC and then transported north into the Kuroshio Current and toward Taiwan and Japan, or south toward the southern Philippines and into the Celebes Sea by the Mindanao Current. Available evidence indicates that A. marmorata may have potentially year-round spawning, and the presence of a spawning area of this species in the same region as that of Anguilla japonica suggests that the northern population of A. marmorata has evolved a spawning migration from East Asia, the Philippines and the Celebes Sea region to the NEC area, but differs from A. japonica by having some individuals that recruit to more southern areas.

The early life history of the tropical eel Anguilla marmorata (Quoy & Gaimard, 1824) from four Pacific estuaries, as revealed from otolith microstructural analysis

Anguilla marmorata glass eels or elvers were collected separately during anadromous migration from four Pacific estuaries: Hamuta, Poso, Shuang Hsi and Tanshui. The total length at arrival in these estuaries was (mean ± standard error) (51.50 ± 0.90) (51.80 ± 0.90) (46.95 ± 0.84) and (47.33 ± 0.80) mm, respectively. The sagittal otolith microstructure, increment patterns and daily age were examined by scanning electron microscope. Based on the number of increments of presumed daily deposition, the overall mean age at arrival in the estuaries was estimated to be about 3–4 months, with an estimated period of 73–86 days for the leptocephalus stage. Two zones, i.e. the leptocephalus growth zone (L) and the metamorphosis growth zone (M) were recognizable in the otolith cross section. The increment width of L and M varied from the otolith's centre to its margin, reflecting different growth rates. The spawning grounds of these eels are presumably not far from the estuary. Their locations are discussed.