The Role of 5-HT and DA Receptor Genes in Starvation-Induced Anxiety Behavior of Portunus trituberculatus

Background/Objectives: Intraspecific aggression and cannibalism severely reduce survival in aquaculture of the Japanese swimming crab, Portunus trituberculatus. Starvation can induce stress-related behavioral changes and alter aggressive behavior in animals, but its behavioral and neurochemical effects in crustaceans remain poorly understood. This study aimed to characterize starvation-associated behavioral changes in P. trituberculatus and to examine their associations with hemolymph serotonin (5-HT) levels, 5-HT1, 5-HT2, and DA1 expression, and aggressive behavior. Methods: Male P. trituberculatus (16 ± 1 g) were randomly assigned to starvation durations of 0–12 days. Starvation-associated behavioral responses were assessed with an underwater light–dark maze and open-field test, and video-recorded behavioral trajectories were analyzed. Hemolymph 5-HT was measured by ELISA. Aggressive behavior was recorded after pairing crabs showing different starvation-associated behavioral states. Expression of 5-HT1, 5-HT2, and DA1 genes in multiple tissues was detected by RT-qPCR. Results: Starvation for 3–6 days significantly reduced time spent in the light arm and center zone, together with decreased hemolymph 5-HT levels. At 7–8 days, time spent in these zones increased and 5-HT levels increased, whereas these behavioral indices decreased again after 9 days. Starvation-associated behavioral changes were associated with reduced attack frequency and attack duration. Moreover, crabs showing starvation-associated behavioral changes showed altered expression of 5-HT1, 5-HT2, and DA1 genes in muscle and eyestalk after aggressive encounters.