Thanatosis in the Brazilian seahorse Hippocampus reidi Ginsburg, 1933 (Teleostei: Syngnathidae)

The present study reports thanatosis behavior in Hippocampus reidi seahorses. We observed two different types of tonic immobility during seahorse handling, both in the laboratory and in field studies. In the former, the seahorses assumed a stretched posture, and in the latter, pointed their heads towards their bellies and curled their tails in a spiral towards their abdomen. The displays lasted 124 +/- 100 s (n = 3) in the laboratory and 155 +/- 7.07 s (n = 5) in the field. Camouflage is the seahorses primary defense from predators and our observations suggest that thanatosis is a secondary strategy that could be more effective than retaliation or escaping predators, due to the fact that seahorses lack teeth and have limited swimming ability. The responses caused by fear occurred after manipulation, allowing for the conclusion that the seahorse H. reidi may use thanatosis as a secondary defense strategy under major stress events.