Ontogenetic changes in the spatial learning capability of jack mackerel Trachurus japonicus

Area of Science:

• Marine biology
• Animal behavior
• Fish ecology

Background:

• Juvenile fish undergo significant developmental changes affecting behavior and habitat.
• Understanding ontogenetic shifts in learning is crucial for fish ecology and conservation.
• Jack mackerel (Trachurus japonicus) juveniles transition between pelagic and coastal habitats during development.

Purpose of the Study:

• To investigate how learning capabilities change during the ontogeny of jack mackerel juveniles.
• To determine if learning ability is size-dependent in juvenile jack mackerel.
• To correlate changes in learning with the ontogenetic habitat shift in this species.

Main Methods:

• Studied jack mackerel juveniles (20–95 mm standard length) from pelagic and coastal habitats.
• Assessed learning capability using simple spatial conditioning (Y-maze) and reversal learning tasks.
• Analyzed the relationship between standard length and learning performance scores.

Main Results:

• Simple reward conditioning scores showed no significant dependence on standard length.
• Reversal learning task performance exhibited a sigmoidal increase with standard length, with an inflexion point at 51.7 mm.
• The improvement in reversal learning coincided with the typical size of recruitment from pelagic to coastal habitats.

Conclusions:

• Reversal learning capability in jack mackerel juveniles significantly increases with size, particularly around the critical recruitment stage.
• This ontogenetic increase in cognitive flexibility may be an adaptation to the more complex coastal environment.
• The findings highlight the interplay between development, learning, and habitat transition in marine fish.