Abstract
Background: Ariosoma-type leptocephali of the congrid subfamily Bathymyrinae are typically present in tropical and subtropical regions where they reach large sizes and are often abundant compared to other taxa. Different morphological species types of these larvae have been documented in the Indo-Pacific region, but few have been matched with their adult species, and their life histories are not known. Results: A sampling survey for leptocephali off western Sumatra, Indonesia, collected 297 Ariosoma-type leptocephali of at least 12 different species of both the exterillium gut and non-exterillium gut types that could be distinguished using morphological characteristics. These leptocephali were collected at 23 of 24 stations over deep water but were not caught at two stations over the shelf between Sumatra and Java. They were most abundant in the 15- to 50-mm size range, but six species were also collected with sizes of > 140 mm, some of which were undergoing metamorphosis at sizes of 143 to 324 mm. Larvae of Ariosoma scheelei were most abundant, with small larvae of ≤ 25 mm present near Sumatra and the Mentawai Islands and larger larvae also present offshore. The other abundant larval types, sp. 1 and Ariosoma sp. 7 showed a different tendency with their small larvae being present more offshore, which suggests different spawning locations possibly linked to differing adult habitats or spawning behaviors. Conclusions: The presence of at least moderately small leptocephali of most of these species suggests that their adults are present in this region, which indicates that there is a high biodiversity of these small benthic eels on the shelf and slope of the Mentawai Islands region off western Sumatra in the eastern Indian Ocean.
Highlights
Ariosoma-type leptocephali of the congrid subfamily Bathymyrinae are typically present in tropical and subtropical regions where they reach large sizes and are often abundant compared to other taxa
The objectives of this study were to document the possible diversity of this group of marine eels in this area based on the presence of their larvae, briefly examine the life history implications of these catches, and provide information that can be useful for future genetic identification studies to match larvae with their adults for Ariosoma-type leptocephali
Morphological and genetic types Morphological characteristics that were examined in the 297 Ariosoma-type leptocephali collected during the BJ-03-2 sampling survey off western Sumatra indicated that there were at least 12 different species present among the larvae (Table 1). This number of species was confirmed by the mitochondrial DNA (mtDNA) sequence analyses of Ma (2006) who found that there were at least 11 species among the larvae sequenced (Ariosoma sp. 8 was not among the 30 leptocephali preserved in ethanol) which corresponded to the morphological species types (Table 1)
Summary
Ariosoma-type leptocephali of the congrid subfamily Bathymyrinae are typically present in tropical and subtropical regions where they reach large sizes and are often abundant compared to other taxa. Ariosoma-type leptocephali all grow to sizes of at least about 175 mm, and some species can reach up to about 400 mm (Mochioka et al 1982, 1991; Smith 1989a; Strehlow et al 1998; Miller et al 2006b; 2013) These larvae have one to three horizontal rows of myoseptal pigment (a short vertical line of tiny spots on each myoseptum between the myomeres) along the sides of their bodies (Castle 1964, 1968; Blache 1977; Mochioka et al 1982, 1991; Tabeta and Mochioka 1988; Smith 1989a; Miller and Tsukamoto 2004). Morphological characters suggest that Kenyaconger may fit within the group with Ariosoma and the two other genera, but this has not been confirmed
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