Epidermal oxysterols function as alarm substances in zebrafish.

Area of Science:

• Chemical Ecology
• Ethology
• Ichthyology

Background:

• Alarm substances in fish are crucial for anti-predation strategies, signaling danger through cues released from injured skin.
• These 'fear substances' are known in many fish species, particularly Ostariophysi, but their chemical identity remains largely uncharacterized.
• Previous research suggests alarm cues are small molecules that elicit specific behavioral responses.

Purpose of the Study:

• To identify the chemical compounds responsible for fish alarm signaling.
• To investigate the molecular mechanism underlying anti-predation behaviors induced by alarm cues.
• To confirm the role of identified compounds in eliciting fear and stress responses in fish.

Main Methods:

• Utilized zebrafish skin extract and observed anti-predation behaviors as bioassays.
• Isolated and identified two specific compounds: 24-methyl-5α-cholestane-3α,7α,12α,24,28-pentahydroxy 28-sulfate (an oxysterol sulfate) and 5α-cyprinol sulfate.
• Tested the behavioral and physiological effects (cortisol levels) of individual compounds and their mixture on zebrafish.

Main Results:

• Both identified sulfate compounds, individually, induced significant anti-predator behaviors and elevated cortisol levels in zebrafish at nanomolar concentrations.
• A mixture of the two compounds at their natural ratio fully replicated the alarm response elicited by the original skin extract.
• The findings reveal a specific molecular basis for fish alarm communication.

Conclusions:

• Two specific oxysterol sulfates function as key chemical alarm cues in zebrafish.
• These compounds mediate a crucial anti-predation mechanism in fish, involving both behavioral and physiological stress responses.
• This research elucidates the chemical nature of fish alarm substances, advancing our understanding of predator-prey interactions.