<p>Adhesion involves complex regulatory mechanisms in marine organisms, yet the underlying processes remain poorly understood. This study investigated the role of the polian vesicle fluid and neurotransmitters in modulating temporary adhesion in the sea cucumber <i>Apostichopus japonicus</i>. In the present study, behavioral assays and biochemical analyses showed that polian vesicle fluid more significantly enhanced the adhesion of sea cucumber than coelomic fluid. Meanwhile, the present study further revealed the regulatory effect of polian vesicle fluid on the adhesion capacity of sea cucumber. Key ions (K⁺, Na⁺, Ca²⁺) showed no consistent correlation with adhesion capacity, whereas 5-hydroxytryptamine (5-HT) elevated in polian vesicle fluid of sea cucumbers with the strong adhesion. Experiments revealed that 5-HT increased adhesion efficiency, while its inhibitor attenuated this effect. In contrast, acetylcholine (ACh) and its inhibitors had no significant effect in this experiment. Heated polian vesicle fluid retained its adhesion properties. These findings establish the polian vesicle as a key organ, and highlight 5-HT as a critical regulator in the temporary adhesion of <i>A. japonicus</i>. The present study enriches our understanding on adhesion mechanisms in marine organisms, and offers new insights into sea cucumber aquaculture.</p>