Crayfish Aggression after Injections of 5-hydroxytryptamine and Lysergic Acid Diethylamide

Crayfish are aggressive creatures who display a dominance hierarchy based on size.  Smaller crayfish retreat from aggressive encounters with larger crayfish.  Previous research found that administering 5-hydroxytryptamine (5-HT) decreases the likelihood a small crayfish will retreat in an encounter with a larger opponent leading to more overall aggression between the pair (Huber, 2001.) To the best of our knowledge, the effect of lysergic acid diethylamide (LSD) on crayfish behavior has not been previously investigated. For this pilot study, smaller crayfish were repeatedly paired each of three larger crayfish in three conditions: control, 20mg/kg of 5-HT, or .003mg/kg of LSD.  The first of the three large crayfish was placed into the fight tank and successively faced each of the smaller opponents in the control condition. This was followed by placing the next large crayfish into the fight tank to face the three smaller opponents and finally the third large crayfish faced in succession the three smaller opponents. Smaller crayfish had approximately 16 min of rest between rounds.  On day two, 20mg/kg of 5-hydroxytryptamine (5-HT) was administered to a smaller crayfish immediately prior to its first fight.  The behavior of the smaller crayfish was coded every 10 sec for 8 min using a Likert scale ranging from 1 (retreats from opponent) to 4 (uses its claws in attempt to injure opponent.)  On the final day, .003mg/kg was administered to each small crayfish and they were coded as in day two.  Chi-square analysis for crayfish by drug condition was significant, X2= 12.1, p = 0.0024, <.01.