Serotonin: A Multifunctional Molecule in Crustaceans

ABSTRACT Serotonin is an ancient monoamine neurotransmitter and hormone that has existed for millions of years, from prokaryotic life forms to modern humans. It is also commonly known as 5‐hydroxytryptamine (5‐HT). In mammals, it is well known for its actions in depression, aggression, anxiety, stress, and sexual behavior. In crustaceans, this molecule plays some vital roles in agonistic behavior, which is the main cause of economic loss in many crustacean (e.g., crayfish and crab) farms. 5‐HT is commonly used to induce reproduction and can potentially be used as an alternative treatment for unilateral eyestalk ablation. This neurotransmitter has direct effects on development, molting, growth, feeding, digestion, and gut microbiota. It is also the main regulator of stress response, osmoregulation, and, to a lesser extent, energy homeostasis in crustaceans. Further, the immune and antioxidant systems and intermediary metabolism are affected by 5‐HT administration. 5‐HT regulates almost all physiological mechanisms in crustaceans. Antidepressant drugs that inhibit 5‐HT reuptake are used for treating behavioral disorders, but their toxicological impacts on the environment are a severe threat. Despite this massive range of actions, no review has ever been conducted to provide an overview of 5‐HT roles in any aquatic species. In this review, these physiological mechanisms are discussed, and suggestions for future directions for research and aquaculture are provided.