Effects of various photoperiods and specific wavelengths on circadian rhythm in ornamental cleaner shrimp Lysmata amboinensis

Abstract

The cleaner shrimp, Lysmata amboinensis, is an ornamental crustacean that is important both commercially, in the aquarium industry, and ecologically, owing to its symbiotic relationship with host fishes. Cleaner shrimp display high daytime activity, unlike other crustaceans, and are highly sensitive to light, particularly, in the 480-540 nm range. However, there have been few studies on the physiological characteristics of this species. In this study, we investigated effect of photoperiod and specific wavelength on the circadian rhythm of cleaner shrimp. Circadian rhythm was evaluated by quantifying the mRNA expression of clock genes such as lysmata amboinensis cryptochrome1 (laCry1) and lysmata amboinensis period 2 (laPer2) and melatonin concentration. The mRNA levels of clock genes were significantly higher at daytime than at night-time. Furthermore, at the red and green wavelengths, the difference in clock gene mRNA levels between day and night was significantly higher than that observed under white fluorescent light. Melatonin levels showed the opposite trend. Collectively, our findings demonstrate that the photoperiod regulates the biological rhythm of the cleaner shrimp and that the irradiation wavelength affects the biological rhythm. In particular, the red and green wavelengths appeared to be linked to the clock gene rhythm and melatonin levels.