Changes in post- and pre-capture escape ability over development in juvenile Japanese eels
Assistant Professor Yuha Hasegawa and Associate Professor Yuuki Kawabata from the Graduate School of Integrated Science and Technology, Nagasaki University, have revealed that juvenile Japanese eels (Anguilla japonica) develop the ability to escape through the gill openings of predatory fish after being swallowed, as they progress through the settlement stage (glass eel stage).
Escape Mechanism of Japanese Eels
・Juvenile Japanese eels (Anguilla japonica) develop the ability to escape through the gill openings of predatory fish after being swallowed.
・This behavior is unique among fish and represents an active post-capture defensive strategy.
Ontogenetic Development of Escape Ability
・The study examined eels from the early glass eel stage (VIA0, VIA1) to the yellow eel stage.
・Early-stage glass eels could not escape, but by the VIA2 stage, 28.1% of individuals successfully escaped via the predator’s gills.
Correlation with Habitat Transition
・The timing of this escape ability development aligns with the eel’s transition from estuaries to freshwater habitats (settlement phase).
・This suggests that the ability is crucial for survival during this vulnerable period.
Pre-Capture vs. Post-Capture Defense Strategies
・While the escape ability develops early (VIA2 stage), pre-capture attack avoidance (evading predator attacks before being swallowed) improves later, in the elver and yellow eel stages.
・This indicates a shift in defensive tactics as the eels mature.
Conservation Implications
・Understanding these developmental changes can aid in conserving and managing the declining population of Japanese eels.
・Insights from this study may help refine strategies for eel restocking and habitat protection.
Predation is one of the major forces driving the evolution of defensive tactics in prey. Recently, post-capture active escape behaviors of different prey animals from the predator’s digestive tract have been reported. However, no studies have yet examined when these escape behaviors are developed through the ontogeny of the prey. This study examined the ontogenetic change in a unique defensive tactic of juvenile Japanese eels Anguilla japonica in which they escape via the predator’s gills after being captured. We used A. japonica ranging in stage from pre-settlement glass eels to post-settlement yellow eels (based on their habitat change from tidal estuaries to freshwater rivers). The results indicated that individuals in the 2 earliest stages of glass eels (stages VIA0 and VIA1) never escaped after being captured, while 28.1% of individuals after the middle glass eel stages (VIA2 and later stages) escaped via the predator’s gill. The ontogenetic timing of the development of escape ability coincides with when eels settle into benthic riverine and estuarine habitats as suggested by previous studies. Additionally, the pre-capture attack avoidance ability of Japanese eels improved rapidly with growth in the subsequent elver and yellow eel stages. These results suggest that the unique post-capture defensive tactic of eels may be particularly important during the vulnerable period around the settlement phase when they are less capable of avoiding predator attacks. Our study offers valuable insights into the behavioral ecology and conservation of anguillid eels, which have faced considerable population declines.
KEY WORDS: Escape behavior · Predator–prey interaction · Recruitment · Behavioral ontogeny · Anguilla japonica · Post-capture defensive tactics · Metamorphosis · Settlement
Journal: Marine ecology progress series（Impact Factor = 2.2）
Title: Changes in post- and pre-capture escape ability over development in juvenile Japanese eels
Author: Yuha Hasegawa1, Kazuki Mine1, Nobuto Fukuda2, Kazuki Yokouchi3, Yuuki Kawabata1
1Graduate School of Fisheries and Environmental Sciences, Nagasaki University, Bunkyo, Nagasaki 852-8521, Japan
2Fisheries Technology Institute, Japan Fisheries Research and Education Agency, Yokohama 236-8648, Japan
3Fisheries Resources Institute, Japan Fisheries Research and Education Agency, Yokohama 236-8648, Japan
Publication date: January 16, 2025
