Positive buoyancy in eel leptocephali: an adaptation for life in the ocean surface layer

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

“…This transformation reportedly causes drastic reductions in the length and weight of the leptocephalus and an estimated 80% drop in whole body water (Bertin 1951;Otake 2003). Previous studies found that the body shape of the leptocephalus is suitable for drifting with oceanic currents (Miller 2009;Tsukamoto et al 2009;Tsukamoto et al 2011). Also, the laterally compressed willow leaf-like body shape of the anguillid leptocephalus and the high body water content greatly contribute to its buoyancy and is favorable for passive planktonic drift and transport by ocean currents, while the body of the glass eel is more adapted for bottom dwelling.…”

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

“…Other anguilliform leptocephali showed osmolalities in a similar range, with the lowest value recorded from a nettastomatid (483), and the highest from a congrid (1057) (Hulet and Robbins 1989). Tsukamoto et al (2009) reported a mean value of 450 mOsm kg -1 H 2 O for the extracellular matrix of A. japonica leptocephali that were reared in the laboratory, and suggested that this low osmolality is likely an important factor in their buoyancy.…”

“…Buoyancy of leptocephali during their ontogeny was also examined by Tsukamoto et al (2009) using artificially spawned and reared eggs and larvae of A. japonica. Preleptocephali had very low specific gravities, probably due to their oil globule, but once the globule was absorbed and the larvae were ready to initiate feeding, their specific gravities increased (Fig.…”

Ontogenetic changes in phototactic behavior during metamorphosis of artificially reared Japanese eel Anguilla japonica larvae

“…Faster swimming speeds are also possible for these leptocephali, as has been observed recently for largersized leptocephali and glass eels of 2 species of eels in the Atlantic Ocean that were tested in the laboratory (Wuenschel & Able 2008). A positive buoyancy of leptocephali (Tsukamoto et al 2009) may tend to accelerate the ascending speed and reduce the diving speed. The faster side movement speed observed in the present study may be related to swimming behavior typically used as an escape reaction that was triggered in response to the bright light irradiated from an unexpected direction.…”