Sensitivity of Anguilliformes leptocephali to metamorphosis stimulated by thyroid hormone depends on larval size and metamorphic stage.

Yutaka Kawakami

Comparative biochemistry and physiology. Part A, Molecular & integrative physiology 2023 Feb

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Metamorphosis of teleosts including Anguilliformes is well known to be induced by thyroid hormone (TH), although the underlying mechanism is not fully understood. In this study, we investigated the experimental conditions needed to induce normal metamorphosis in artificially spawned Japanese eel (Anguilla japonica), including initial larval size, TH concentration, and timing of TH immersion. Around 37 mm TL was found to be the minimum size of larvae that underwent successful metamorphosis induced by l-thyroxine (T4); notably, smaller larvae did not show increased expression of TH receptors in response to T4, suggesting that small leptocephali are not sufficiently responsive to TH. Furthermore, successful completion of metamorphosis depended on sensitivity to TH, which changed with metamorphic stage; for example, prolonged exposure to higher TH concentrations led to morphological defects. Collectively, these results reveal that the induction of metamorphosis by TH is dependent on larval size, and that the concentration of TH must be adjusted in line with metamorphic stage to achieve successful progression of metamorphosis. Our findings will contribute to improving production technology in the aquaculture of Japanese eels by facilitating the earlier induction of metamorphosis in artificial leptocephali. Copyright © 2022 Elsevier Inc. All rights reserved.

Citation

Yutaka Kawakami. Sensitivity of Anguilliformes leptocephali to metamorphosis stimulated by thyroid hormone depends on larval size and metamorphic stage. Comparative biochemistry and physiology. Part A, Molecular & integrative physiology. 2023 Feb;276:111339