Red fluorescence increases with depth in reef fishes, supporting a visual function, not UV protection

Area of Science:

• Marine Biology
• Animal Behavior
• Biophotonics

Background:

• Some marine fish species display natural red fluorescence, particularly in their eyes.
• Two hypotheses explain this phenomenon: photoprotection from UV radiation or enhanced visual contrast in deeper waters.

Purpose of the Study:

• To investigate the ecological function of red fluorescence in marine fish.
• To differentiate between the photoprotection and visual contrast hypotheses for red fluorescence.

Main Methods:

• In vivo fluorometry was used to measure red fluorescence brightness.
• Measurements were taken from eight common reef fish species at depths of -5 m and -20 m.

Main Results:

• Red fluorescence was significantly brighter in fish from -20 m compared to -5 m in six of eight species.
• This finding supports the visual contrast hypothesis.

Conclusions:

• Red fluorescence in marine fish likely functions to enhance visual contrast in deeper, low-light environments.
• Eye-specific fluorescence may aid in detecting cryptic prey, impacting fish visual ecology.