The behavioral detection of binary mixtures of amino acids and their individual components by catfish

The question of whether a binary mixture of amino acids is detected by fish as a unique odor or whether the qualities of the individual components are retained within the mixture was investigated in channel (Ictalurus punctat us) and brown bullhead (Ameiurus nebulosus) catfish, species that are highl y similar in their olfactory receptor and behavioral responses to amino aci d odorants, Catfish respond with greater appetitive food-searching (swimmin g) behavior to amino-acid-conditioned olfactory stimuli than to non-conditi oned amino acids. In the present study, appetitive food-searching behavior was measured by counting the number of turns of the fish greater than 90 de grees within 90s of stimulus onset and, in some tests, by video tracking. T he two methods yielded highly correlated results. Channel catfish condition ed to a binary mixture composed of equimolar amino acids responded with sea rching behavior to the amino acid that produced the larger-amplitude electr o-olfactogram (EOG) response as they did to the conditioned stimulus. In fu rther studies, bullhead catfish were conditioned either to a binary mixture or to a single amino acid and tested to determine whether a binary mixture was detected as the component evoking the larger EOG response. In all init ial tests (trials 1-3), the more stimulatory component of a binary mixture was not discriminated from the binary mixture; however, the less stimulator y component and all other amino acids tested were discriminated from the mi xture. By increasing the concentration of the originally less potent compon ent in a binary mixture, making it the more stimulatory compound, it was no w detected as not significantly different from the binary mixture; however, the original more potent component (i.e. now the less potent stimulus) was detected as significantly different from the mixture, However, with 5-10 a dditional discrimination training trials, the less stimulatory component in a binary mixture influenced the perception of the binary mixture because t he binary mixture was no longer detected only as its more stimulatory compo nent. The data suggest that a two-step learning process occurs within the o lfactory bulb and possibly higher-order telencephalic nuclei.