Search

Melatonin affects physiological processes that have circadian and seasonal cycles and causes behavioural changes in nearly all organisms, ranging from bacteria to mammals. However, no studies have focused on the presence, biosynthetic pathway, and rhythms of melatonin in bivalves, which are considered as the class of molluscs with the highest economic value. Here, the metabolic pathway and tissue distribution of melatonin, tissue transcription profiles of melatonin-related genes [key synthases arylalkylamine N-acetyltransferase type 2 and 5 (aanat2 , aanat5), N-acetylserotonin methyltransferase (asmt), and melatonin receptor type 1 A1 and C3 (MTNR1A1 , MTNR1C3)], daily changes in melatonin, transcripts of genes, and effects of four lights (blue, cyan, orange, and red) during the night on melatonin secretion were studied in a bivalve species, razor clam Sinonovacula constricta. Our results showed the presence of complete metabolic and circadian entrainment pathways of melatonin. The melatonin content in the lymphocytes and labial palp was higher than that in the other studied tissues, and aanat2 , aanat5 , asmt , MTNR1A1 , and MTNR1C3 mRNA levels were the highest in the labial palp. Melatonin fluctuated rhythmically in lymphocytes and labial palps and increased at night. Similarly, aanat2 , aanat5 , asmt , MTNR1A1 , and MTNR1C3 mRNA levels were rhythmic in the labial palp, peaking at night. In addition, blue light effectively inhibited the nocturnal secretion of melatonin in the clam. In summary, our results suggest that melatonin plays a role in light signal transduction and the circadian system in S. constricta. • Melatonin could be biosynthesized by the clam Sinonovacula constricta. • Labial palp probably is an important tissue where melatonin exerted its function. • The biosynthesis and secretion of melatonin in the clam are enhanced under the dark phase of the photoperiod. • Blue light inhibits melatonin production in the clam. [ABSTRACT FROM AUTHOR]

In the present study, we explored the effects of seven light treatments (white, violet, blue, cyan, green, yellow, and red) on juvenile Sinonovacula constricta (length, 693.79 ± 82.91 μm), employing dark treatment as a control. A rearing experiment was conducted for one week in which the feeding rate was examined daily, e.g., one, two and three h after feeding. At the conclusion of the experiment, overall growth was calculated, and enzymatic activity related to digestion, superoxide dismutase, catalase, and glutathione peroxidase pertaining to antioxidant biomarkers, as well as expression levels of genes related to antioxidation and stress response, were examined. The results showed that the highest growth rates were observed in the yellow light group, while the lowest growth rates were found in the violet and blue light groups; on the other hand, no significant differences were found among the other groups. Meanwhile, when exposed to white, yellow, or green light, juveniles exhibited high feeding rates, while those in the violet and blue light groups showed low feeding rates. Regarding enzymatic activity related to digestion, those of α -amylase, lipase, pepsin, and trypsin were relatively higher in the yellow light group than in the other groups. Regarding oxidative stress, the yellow light group showed higher superoxide dismutase, catalase, and glutathione peroxidase activities than the other groups. In contrast, the lowest malonaldehyde level was found in the white light group, followed by yellow light, while there were no significant differences among the other groups. In addition, the expression levels of genes related to antioxidation and stress response (heat shock protein 70 and glucose-regulated protein 78) in juveniles generally exhibited higher levels in the red light group, whereas they showed relatively lower levels in the yellow light group. Collectively, these results suggest that the application of yellow light may facilitate the growth of juvenile S. constricta , while red and violet light have opposite effects. • Light spectrum differently influenced the growth of juvenile S. constricta. • Yellow light facilitated the growth of juvenile S. constricta. • Yellow light induced less stress to S. constricta. • Red and violet lights impaired the growth of juvenile S. constricta. [ABSTRACT FROM AUTHOR]

Sinonovacula constricta is an important bivalve with strong photosensitivity and a robust circadian rhythm. To elucidate the light entrainment of the molecular circadian clock in this species, this study identified the clock genes, characterized their tissue distribution, and investigated their transcriptional variations under different light regimes: LD (12 h light/12 h dark cycle), LL (continuous light), and DD (continuous dark). The results showed that the S. constricta clock system consists of seven genes [ Circadian locomotor output cycles kaput (ScClock), Brain and muscle ARNT-like protein (ScBmal), Cryptochrome (ScCry1 and 2), Period (ScPer), and Timeless (ScTimeless1 and 2)] that are closely related to their orthologs in marine mollusks and contained corresponding conserved functional regions, indicating the conserved evolution of the circadian clock among organisms. These genes were expressed in all tissues, with high expression in the labial palps and hepatopancreas, suggesting a complex peripheral biological clock in S. constricta and the critical role of these two tissues in circadian functions. When exposed to different light regimes in labial palps, genes from the positive loop (ScClock and ScBmal) displayed a daily/circadian rhythm under both LD and DD and their acrophases were shifted by 5–7 h, whereas genes from the negative loop displayed daily rhythms (ScCry1 and ScPer) under LD and circadian rhythms (ScCry2 and ScTimeless2) under DD. However, only one gene (ScTimeless2) displayed a circadian rhythm under LL conditions. These results suggest that the S. constricta circadian system may be regulated by different clock genes to adapt to various light environments. Although similar phenomena were observed in the hepatopancreas, markedly different clock gene expression patterns occurred between the two tissues, indicating a tissue-specific regulated circadian system. Collectively, this study reveals how the circadian oscillators of S. constricta respond to light and may promote light environment optimization in the S. constricta farming industry. • The molecular circadian clock was conserved in S. constricta. • A peripheral and tissue-specific clock might exist in S. constricta. • The S. constricta circadian clock was synchronized by photoperiod. • A functional clock exists in S. constricta. [ABSTRACT FROM AUTHOR]

In the present study, we aimed to explore the optimal light intensity for the breeding of Sinonovacula constricta , and the effect of light intensity on the growth of S. constricta at different developmental stages was studied. Four developmental stages (spawning, fertilized eggs, planktonic larvae, and juveniles) and different light intensities were set up in our current experiments. The results showed that various light intensities had significantly different effects on spawning amount and initial spawning time, while it had little influence on the hatchability of fertilized eggs (P > 0.05). The spawning amount of the razor clam peaked at a light intensity of 44–250 lx (P < 0.05). In the planktonic larvae experiment, the highest survival rate appeared at 487 ± 31 lx (58.61 ± 4.0%).For juvenile S. constricta , two substratum thicknesses (1 and 5 mm) and four light intensities, including L 1 (14 ± 11 lx), L 2 (380 ± 145 lx), L 3 (3792 ± 2105 lx), and L 4 (12,244 ± 5290 lx), were set up in a 10-day experiment. When the substratum thickness of 1 mm was applied, the body length and survival rate of S. constricta juveniles (0.26 ± 0.02 mm) in the L 2 group were found to be the largest, which were significantly different compared with the other groups. When the substratum thickness was changed to 5 mm, the body length and survival rate among those groups showed no significant difference. However, when the shellfish samples were changed to a larger size of razor clam (1.45 ± 0.16 mm), a more obvious effect of light intensity on the growth was observed in a 1-mm substratum group compared with the 5-mm group. These results indicated that light intensity exerted a significant effect on the growth of S. constricta at different stages, and each stage exhibited a distinct sensitivity to light intensity. Further study from the aspects of photoreceptors and relevant genes is currently in progress in our laboratory. • Spawning, hatching and growth of S. constricta were affected by light intensity. • All developmental stages of S. constricta were photosensitive, except zygote. • Optimal light intensity is critical for S. constricta breeding and farming. [ABSTRACT FROM AUTHOR]