Evidence that Gulf toadfish use pulsatile urea excretion to communicate social status

Gulf toadfish (Opsanus beta), a highly territorial marine teleost species, are believed to communicate through chemicals released across the gill during pulsatile urea excretion. While freshwater teleost and crustacean urinary signals have been shown to relay information about dominance to reduce physical aggression in future encounters, the use of chemical signals to convey social status in marine teleosts is understudied. Behavior and urea excretion patterns were monitored in pairs of male toadfish during an initial agonistic encounter and in a 2^nd encounter where a subset of pairs had their nares blocked to determine how olfaction, and thus chemical communication, play a role in establishing dominance. Anosmic toadfish did not experience increases in aggressive behavior, unlike other species previously studied. However, behavior and the pattern of urea excretion were disrupted in anosmic pairs compared to control pairs. Specifically, control subordinate fish had an increase in their dominance index during the 2^nd encounter, a response that anosmic subordinate fish did not experience suggesting that without the ability to smell, subordinate fish cannot recognize their opponent and assess their fighting ability and have a reduced chance of winning. These anosmic subordinate fish also had an increase in pulse frequency, perhaps reflecting an increased effort in communication of status. Future research is needed to conclude if peaks in agonistic behavior are coordinated around the time of urea pules. However, the observed changes in behavior and pulsatile urea excretion due to anosmia in the present study provide evidence that toadfish use pulsatile urea excretion to release signals for chemical communication during agonistic encounters.