Anxiety induces long-term memory forgetting in the crayfish

Efficacy of Administration Routes in Crayfish: Comparative Analysis of Intracoelomic and Intrapericardial Techniques Using Fluorescein Dye

Crayfish are emerging as model organisms for various disciplines. Moreover, decapod crustaceans also exhibit pain-like reactions and heightened anxiety when exposed to harmful stimuli, leading to short-term or persistent behavioral shifts. Awareness of decapod crustacean sentience and thus, suffering calls for refinement of current laboratory protocols. This study aims to enhance the standard methodology for injecting substances into crayfish by minimizing stress-inducing manipulation. We examined the impacts of various administration routes on the persistence of injected chemicals in marbled crayfish, its excretion, and animal survival. Fluorescein dye was used as a visual marker. It was administered via three alternative injection routes-intracoelomic (IC), intrapericardial administration through areola (IP-A), and intrapericardial administration through arthrodial membrane (IP-AM). Continuous video observations were made for a 4-h period under UV light, followed by intermittent observations at 12-h intervals over 48 h. The highest mortality (20%) was observed in IP-A administration. The IP-A method also provided the fastest systemic distribution of the dye in the body. Results indicated visibly higher urination frequency in IP-AM compared to IP-A. IC mirrored IP-AM outcomes without any observed mortality. We conclude that IC administration proved superior to intrapericardial methods, offering the least harmful but effective approach for crayfish injections.

Serotonin and dopamine regulate the aggressiveness of swimming crabs (Portunus trituberculatus) in different ways

Bioamines act as a pivotal part in the regulation of aggressive behavior in animals as a type of neuroendocrine, but the patterns of how they regulate aggressiveness in crustaceans are still unclear due to species-specific responses. To determine the effects of serotonin (5-HT) and dopamine (DA) on the aggressiveness of swimming crabs (Portunus trituberculatus), we quantified their behavioral and physiological characteristics. The results showed that an injection of 5-HT at 0.5 mmol L^-1 and 5 mmol L^-1 could significantly enhance the aggressiveness of swimming crabs, as well as an injection of DA at 5 mmol L^-1. The regulation of 5-HT and DA on aggressiveness is dose-dependent, and these two bioamines have different concentration thresholds that can trigger aggressiveness changes. 5-HT could up-regulate the 5-HTR1 gene expression and increase lactate content at the thoracic ganglion as the aggressiveness enhances, suggesting that 5-HT may activate related receptors and neuronal excitability to regulate aggressiveness. As a result of DA injection at 5 mmol L^-1, lactate content in the chela muscle and hemolymph increased, glucose content in the hemolymph increased, and the CHH gene was significantly up-regulated. Pyruvate kinase and hexokinase enzyme activities in the hemolymph increased, which accelerated the glycolysis process. These results demonstrate that DA regulates the lactate cycle, which provides substantial short-term energy for aggressive behavior. Both 5-HT and DA can mediate aggressive behavior in the crab by activating calcium regulation in muscle tissue. We conclude that the enhancement of aggressiveness is a process of energy consumption, in which 5-HT acts on the central nervous system to induce aggressive behavior, and DA affects muscle and hepatopancreas tissue to provide a large amount of energy. This study expands upon the knowledge of regulatory mechanisms of aggressiveness in crustaceans and offers a theoretical foundation for enhancing crab culture management.

Opposing effects of dopamine on agonistic behaviour in crayfish

The effects of dopamine on the agonistic behaviour of crayfish were analysed. When dopamine concentrations of 1 μmol l-1 were injected into large crayfish, individuals were beaten by smaller opponents, despite their physical advantage. Injection of 10 μmol l-1 dopamine into small animals increased their rate of winning against larger opponents. Injection of a D1 receptor antagonist prohibited the onset of a 'loser' effect in subordinate animals, suggesting that the inhibitory effect of dopamine on larger animals is mediated by D1 receptors. Similarly, injection of a D2 receptor antagonist prohibited the onset of a 'winner' effect in dominant animals, suggesting that the facilitating effect of dopamine on small animals is mediated by D2 receptors. Since the inhibitory effect of 1 μmol l-1 dopamine was similar to that seen with 1 μmol l-1 octopamine and the facilitating effect of 10 μmol l-1 dopamine was similar to that of 1 μmol l-1 serotonin, functional interactions among dopamine, octopamine and serotonin were analyzed by co-injection of amines with their receptor antagonists in various combinations. The inhibitory effect of 1 μmol l-1 dopamine disappeared when administered with D1 receptor antagonist, but remained when combined with octopamine receptor antagonist. Octopamine effects disappeared when administered with either D1 receptor antagonist or octopamine receptor antagonist, suggesting that the dopamine system is downstream of octopamine. The facilitating effect of 10 μmol l-1 dopamine disappeared when combined with serotonin 5HT1 receptor antagonist or D2 receptor antagonist. Serotonin effects also disappeared when combined with D2 receptor antagonist, suggesting that dopamine and serotonin activate each other through parallel pathways.