Circadian rhythms of melatonin in haemolymph and optic lobes of Chinese mitten crab (Eriocheir sinensis) and Chinese grass shrimp (Palaemonetes sinensis)

摘要

This study is the first to examine the circadian rhythms of melatonin in Eriocheir sinensis and Palaemonetes sinensis, two economically important crustaceans. We collected haemolymph and optic lobes from both species every 4 h over a whole day cycle. Melatonin content was measured with high-performance liquid chromatography. E. sinensis haemolymph exhibited significant (p < 0.05) peaks in melatonin at 16:00 (0.180 +/- 0.020 mu g center dot mL(-1)) and 24:00 (0.244 +/- 0.055 mu g center dot mL(-1)), while eyestalks had significant peaks at 16:00 (72.377 +/- 18.100 mu g center dot eyestalk(-1)) and 24:00 (98.756 +/- 30.271 mu g center dot eyestalk(-1)). In P. sinensis, melatonin peaked significantly only at 16:00 in optic lobes (12.493 +/- 1.475 mu g center dot eyestalk(-1)) (p < 0.05); no significant peaks were present in haemolymph. Thus, both E. sinensis and P. sinensis exhibit species-specific melatonin rhythms. Time of day should therefore be considered when examining the physiological status of both crustaceans, given the potential influence of fluctuating daily melatonin concentrations.