Abstract

Studies of prey detection by olfaction in teleost fishes have focused largely on amino acids as odorants, while studies with respect to nitrogenous waste are few by comparison. Although threshold sensitivities for amino acids are often in the nano-molar range, gill and renal membranes are thought to be less permeable to amino acids than lower molecular weight compounds such as ammonia or urea. Furthermore, amino acids are generally conserved for protein synthesis and are a minor constituent of excreta. This study examined detection of ammonia, urea, and amino acids by Lutjanus griseus (gray snapper ). Opsanus beta is a preferred prey item of L. griseus. O. beta is unique among teleosts in that adults can faculta-tively shift between ammonia and urea excretion. Experiments were conducted in 8,000 L outdoor mesocosms with flow-through seawater and a sediment/seagrass substrate to simulate natural habitat. Odorants were injected into small experi-mental shelters designed to mimic toadfish burrows. Shelters were equipped with low-light video cameras to remotely monitor snapper behaviours. Results indicate that L. griseus are more responsive to ammonia than either urea or an ammonia/urea mix with threshold sensitivities below 5 ?M. Additionally, L. griseus are more responsive to an amino acid/ammonia mix than either an amino acid/urea mix or amino acids without waste-N. These results suggest that urea masks the aroma of ammonia but not those of amino acids.

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