Fine structure of the drum muscles of the piranha (serrasalminae, characidae)

Area of Science:

• Ichthyology
• Comparative Muscle Ultrastructure
• Fish Anatomy

Background:

• The sound-producing drum muscles of fish are crucial for communication and defense.
• Understanding the fine structure of these muscles provides insights into their function and evolutionary adaptations.

Purpose of the Study:

• To investigate and compare the fine structural characteristics of the anterior and posterior drum muscles in piranha.
• To identify unique ultrastructural features that may relate to the sound-production mechanisms in piranha.

Main Methods:

• Transmission electron microscopy was used to examine ultrathin sections of piranha drum muscles.
• Detailed ultrastructural analysis focused on myofibril organization, sarcomere length, mitochondrial morphology, sarcoplasmic reticulum, and motor endplates.

Main Results:

• Both anterior and posterior drum muscles exhibited slender myofibrils and short sarcomeres.
• Numerous peripheral mitochondria with irregular internal structure and abundant sarcoplasmic reticulum were observed.
• Motor endplates were numerous but lacked the characteristic junctional-fold apparatus; no lipids were detected.
• Posterior drum muscle fibers showed irregular departures from their longitudinal arrangement.

Conclusions:

• Piranha drum muscles display conserved fine structural features, suggesting a specialized adaptation for sound production.
• The absence of a junctional-fold apparatus in motor endplates may represent a unique adaptation in piranha sound-producing muscles.
• The observed ultrastructural characteristics provide a basis for understanding the biomechanics of piranha drumming.