| Summary: | Serotonin (5-HT) is primarily distributed in the gastrointestinal and central nervous systems, where it plays a crucial role in regulating various physiological functions such as digestion, reproduction and establishing animal emotions. 5-HT is an effective oxytocin widely used in molluscan aquaculture, and its physiological functions are performed by binding to corresponding 5-HT receptors (5-HTRs). In this study, seven <i>5-HTR</i> genes of <i>Sinonovacula constricta</i> (<i>Sc5-HTRs</i>) were identified and analyzed, and they were designated as <i>Sc5-HT1A</i>, <i>Sc5-HT1D</i>, <i>Sc5-HT2-1</i>, <i>Sc5-HT2-2</i>, <i>Sc5-HT2-3</i>, <i>Sc5-HT4</i> and <i>Sc5-HT6</i>. Phylogenetic analysis showed that the seven <i>Sc5-HTRs</i> were conserved among mollusks, and the Sc5-HTRs were all transmembrane proteins. The seven <i>Sc5-HTR</i> genes were distributed on chromosome 1, 2, 13 and 14. After injecting 5-HT, there was a significant increase in mRNA expression levels of <i>Sc5-HT1A</i> (<i>p</i> < 0.05) and <i>Sc5-HT2-3</i> (<i>p</i> < 0.01), while <i>Sc5-HT4</i> decreased significantly (<i>p</i> < 0.01) compared to control groups which might be effective 5-HT receptors. Furthermore, two of the receptors (<i>Sc5-HT2-3</i> and <i>Sc5-HT4</i>) were expressed in the circadian rhythm patterns, indicating their potential influence on the nocturnal spawning of <i>S. constricta</i>. Overall, these findings provide a theoretical basis for understanding the structures and functions of <i>5-HTR</i> gene family members, and may facilitate the artificial propagation of mollusks.
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