Comparative study of carp otolith hardness: lapillus and asteriscus

Area of Science:

• Biomineralization
• Vertebrate inner ear biomechanics
• Materials science of biominerals

Background:

• Otoliths are calcium carbonate biominerals crucial for vertebrate balance, movement, and sound perception.
• Freshwater carp possess two otolith types: asteriscus (vaterite) and lapillus (aragonite).

Purpose of the Study:

• To compare the mechanical properties (hardness, modulus, creep) of carp asteriscus and lapillus otoliths.
• To investigate the influence of crystal polymorphs and organic components on otolith mechanical behavior.
• To examine the scale-dependent mechanical responses using nano- and micro-indentation.

Main Methods:

• Nano- and micro-indentation testing on carp asteriscus and lapillus otoliths.
• Analysis of hardness, elastic modulus, and creep behavior.
• Correlation of mechanical properties with crystal structure (vaterite vs. aragonite) and organic content.

Main Results:

• Lapillus (aragonite) demonstrated significantly higher hardness and modulus than asteriscus (vaterite) in both nano- and micro-indentation tests.
• Both otolith types exhibited time-dependent creep, attributed to their organic constituents.
• Nano-indentation revealed higher hardness values than micro-indentation for both otoliths, consistent with scale-dependent strength and flaw population.

Conclusions:

• The distinct crystal polymorphs (aragonite in lapillus, vaterite in asteriscus) are primary determinants of carp otolith mechanical properties.
• Organic components contribute to the observed time-dependent mechanical behavior (creep) in carp otoliths.
• Scale-dependent strength is evident in carp otoliths, with nano-indentation revealing higher hardness due to reduced flaw interaction.