Axial muscle-fibre orientation in developing larval zebrafish.

Area of Science:

• Developmental biology
• Comparative anatomy
• Biomechanics

Background:

• Fast axial muscles are vital for fish escape responses.
• Adult teleosts have pseudo-helical muscle patterns, but larval zebrafish exhibit helical arrangements.
• The developmental timeline of this helical pattern in larval zebrafish is not well understood.

Purpose of the Study:

• To investigate the developmental timeline of muscle fiber orientation in larval zebrafish.
• To determine when the helical muscle pattern emerges and how it changes during early development.
• To compare larval zebrafish muscle patterns with those of adult teleosts.

Main Methods:

• Analysis of muscle-fiber orientation in genetically modified zebrafish from 2 to 13 days post-fertilization (dpf).
• Utilized 3D fluorescence confocal microscopy for detailed imaging.
• Quantified fiber angles relative to the notochord and fitted models to assess helical trajectories.

Main Results:

• A helical muscle fiber pattern is present as early as 2 dpf in larval zebrafish, tapering towards the tail.
• The helical pattern remains stable throughout the first 11 days post-hatching.
• Decreasing projection angle variation towards the tail was observed, especially in younger larvae.
• Helix centers consistently align at corresponding normalized positions along the notochord across developmental stages.

Conclusions:

• The helical muscle fiber arrangement is an early developmental feature in larval fish.
• No pseudo-helical deviations were observed in zebrafish up to 13 dpf, suggesting a distinct developmental trajectory from adult patterns.
• This early helical structure likely plays a role in the rapid escape responses of larval fish.