Does eel metamorphosis cause a breakdown in the tenets of otolith applications? A case study using the speckled worm eel (Myrophis punctatus, Ophichthidae)

Abstract

Several basic tenets of otolith research have been questioned recently with regard to eel metamorphosis. Specifically, some researchers have suggested that otolith increment formation is not daily, and otolith material may be resorped during metamorphosis. We conducted a rearing experiment to test the hypothesis that increment formation is daily and that the otolith continues to grow during eel metamorphosis. We marked the otoliths of wild-caught Myrophis punctatus leptocephali and reared these fish through metamorphosis. Metamorphosis was characterized by a decreasing standard length, pre-anal length, and body depth accompanied by an increase in pigmentation and a change in behavior. Increment formation was daily or near-daily through metamorphosis, and the otolith continued to grow during metamorphosis. Thus, the basic tenets of otolith application apply to eel metamorphosis, and non-daily ring deposition and resorption should not be used as explanations for otolith characteristics of eels (e.g., back-calculated hatch dates) unless demonstrated experimentally.

Ecology of Anguilliform Leptocephali: Remarkable Transparent Fish Larvae of the Ocean Surface Layer

“…Species collected in the mostly warm Indo-Pacific region have growth rates <1 mm/d and linear relationships between age and body length, with growth slowing down as maximum size is reached ( Table 1; . These relationships and the finding of apparent lunar cycles of spawning based on backcalculated hatching dates (Ishikawa et al 2001;Tsukamoto et al 2003;Lee et al 2008), suggest that increments are deposited daily in these species (Powles et al 2006).…”

“…An increase in increment width during metamorphosis was also found in tarpon leptocephali held in the laboratory (Shiao and Hwang 2006;Chen et al 2008). Powles et al (2006) showed that otoliths of ophichthid leptocephali, Myrophis punctatus, continued to deposit increments during metamorphosis, but they did not analyze increment widths. No increase in increment widths were observed in anguillid glass eels that recruited to Iceland however, which may have been due to the cold temperatures and slow metamorphosis experienced by those individuals during their leptocephalus stage (Kuroki et al 2008b).…”

“…4 2009 mismatch of many of their back-calculated hatching dates and the known spawning season of temperate species such as Anguilla rostrata, as indicated by collections of small leptocephali in their spawning area (McCleave 2008). This period when increments are not deposited likely occurs during the glass eel stage because studies on metamorphosing anguilliform and elopiform leptocephali have found that otolith deposition continues during metamorphosis (Chen and Tzeng 1996;Powles et al 2006) and wider increments are formed (Figs. 38, 39).…”

Inshore migration and otolith microstructure/microchemistry of anguillid glass eels recruited to Iceland

“…Cieri and McCleave (2000) proposed that there may be no otolith deposition during metamorphosis in the Atlantic eels, but no heavy check was observed near the otolith increments corresponding to metamorphosis in the Icelandic glass eels examined here. In addition, recent studies on other elopomorph fishes have shown that otolith daily deposition continues through metamorphosis in leptocephali held in the laboratory as they transformed into the glass eel or juvenile stage (Chen and Tzeng 2006;Powles et al 2006). This suggests that if there is a possible period of lack of otolith deposition in the otoliths of some Atlantic glass eels, it is probably not during metamorphosis, but is more likely when the glass eels have reached their recruitment areas and stay on the bottom without feeding or actively migrating inshore.…”

Growth, summer cohort output, and observations on the reproduction of brook silverside, Labidesthes sicculus (Cope) in the Kawartha Lakes, Ontario

“…The tank was suspended in the larger maintenance tank to avoid temperature shock on 7 December 2002, for 12 h, to place a dye mark in the otoliths, as in Tsukamoto (1988). We could then follow subsequent growth and increment number past this mark (as in Powles et al 2006). After 12 h, survivors were replaced in their holding tank.…”