Journal Article Developmental intervals during the larval and juvenile stages of the Antarctic myctophid fish Electrona antarctica in relation to changes in feeding and swimming functions

12pp.88 - 98 , 2017-06
The Antarctic myctophid fish species Electrona antarctica is believed to play a key role in the Southern Ocean food web, but there have been few studies on its early life history. This study examined the developmental changes in the external morphology and osteology of E. antarctica from the early larva to juvenile stages through the transformation phase and inferred changes in its behaviour and feeding mode. Once the larvae reached 12–13 mm body length (BL), they adopted a primordial suction feeding mode along with the acquisition of early swimming capabilities. Thereafter, both swimming and feeding functions were enhanced through fin development and ossification and acquisition of elements of the jaw and suspensorium. These processes indicate that larvae transition from the planktonic to nektonic phase upon reaching 12–13 mm BL when they enhance their both swimming and feeding abilities with growth. Transformation occurred when larvae reached 19–21 mm BL with changes such as discontinuous increases in eye diameter and upper jaw length and the appearance of photophores and dense body pigmentation. Osteological development of swimming- and feeding-related structures were mostly complete after transformation. Rapid changes in external morphology and osteology during the transformation stage are most likely related to ontogenetic vertical migration into deep waters.
本研究は、南大洋外洋域で大きな生物量をもつElectrona antarctica (ハダカイワシ科魚類) の仔魚から稚魚期に至る外部形態と骨格の発育を明らかにし、遊泳・摂餌様式の変化について推定した。仔魚は体長12-13 mmまでに、初期の遊泳能力と吸い込み摂餌能力を獲得し、その後、遊泳・摂餌機能は、鰭の発達と顎と懸垂骨の出現・化骨により強化された。この発育過程は、仔魚が体長12-13 mmで浮遊生活から遊泳生活に移行することを示している。変態は体長19-21 mmで起こり、この期間に、眼径と上顎長の不連続的な増大、発光器の出現、体表面の黒色素胞の出現などが観察された。変態後に遊泳・摂餌機能はほぼ完成した。この変態期の急速な形態的・骨学的変化は、表層から中層への生息域の変化と関連するものと考えられた。

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