Plasma and ocular melatonin rhythms in Amazonian fish

Area of Science:

• * Comparative physiology
• * Chronobiology
• * Aquatic animal research

Background:

• * Melatonin is a key hormone regulating circadian rhythms.
• * Understanding melatonin regulation in fish is crucial for aquaculture and ecological studies.
• * Amazonian fish species have unique adaptations to their environment.

Purpose of the Study:

• * To investigate the daily melatonin rhythms in two Amazonian fish species: Astronotus ocellatus and Brycon amazonicus.
• * To determine the impact of a light pulse on melatonin levels during the dark phase.
• * To assess the potential of photic stimulation as a physiological time cue in these species.

Main Methods:

• * Experiment 1: Fish were subjected to a 12-hour light:12-hour dark cycle with blood sampling every 4 hours.
• * Experiment 2: A 1-hour light pulse was administered during the midpoint of the dark period.
• * Plasma and ocular melatonin levels were measured in both experimental conditions.

Main Results:

• * Both Astronotus ocellatus and Brycon amazonicus displayed peak melatonin levels in the middle of the dark period.
• * An inverted rhythm was observed in ocular melatonin for both species.
• * The light pulse significantly reduced plasma melatonin to daytime levels, while ocular melatonin remained unaffected.

Conclusions:

• * Photic stimulation effectively suppresses plasma melatonin in these Amazonian fish species.
• * Light pulses can serve as a reliable physiological time cue for regulating melatonin production.
• * These findings have implications for managing circadian rhythms in captive fish.