TOADFISH CLOAKED IN UREA

Abstract

When it comes to getting rid of your own waste, it's often best to go for the low cost option. However, when it comes to disposing of metabolic nitrogenous waste, the cheapest alternative, ammonia, is also the most toxic. This isn't a problem for most fish as the toxin is quickly diluted in their environment, but toadfish still seem to go with the high cost alternative:urea. Why toadfish excrete urea had puzzled scientists for decades, until John Barimo and Pat Walsh began wondering what effect urea has on species that prey on these coastal fish. Focusing on the gulf toadfish and one of its predators,the gray snapper, Barimo and Walsh tested how the gray snapper reacted to ammonia and urea in a natural setting. They found that ammonia attracted the predator to the toadfish's hiding place at levels as low as 55 nmol N l-1. However, when the team released mixtures of ammonia and urea from simulated toadfish lairs, gray snappers were much less attracted to the ammonia; urea seemed to `cloak' ammonia and the toadfish's presence(p. 4254). Barimo and Walsh suspect that the fish have opted for this costly waste disposal alternative to conceal themselves from predators, as the benefits far outweigh the expense.