An appetitive olfactory learning paradigm for zebrafish in their home tanks

Olfaction is a subject of increasing interest in fish biology, but there are few learning paradigms available to investigate olfactory behaviour. In the present study, groups of zebrafish were trained in their home tanks retrofitted for automated conditioning with a microprocessor-controlled syringe pump and feeder to deliver odourant and food, respectively, and responses recorded remotely to minimize researcher interference. Fish were presented with phenylethyl alcohol (PEA), and a food reward was given 15 seconds later for experimental groups or at a variably delayed interval for controls. This schedule continued for 48 trials over four days. Both groups showed initial attraction to PEA, but by the end of Day 2 all fish exhibited reduced interest in the odourant. Further experiments with different fish indicated that this attraction was dependent upon high food motivation, as starved animals reacted more than non-starved animals to the novel stimulus. On Day 3, experimental fish began once again to show attraction associated with the odourant, thus indicating that they formed an association between the PEA and food reward, which increased by the end of Day 4. Conversely, control fish showed little or no response to the odourant on Days 3 and 4. When exposed to a water-only trial, trained fish largely ignored the cue, indicating that odour and not turbulence was the main stimulus for learning. This experiment demonstrated that an appetitive learning paradigm, using olfactory cues presented in home tanks, is both feasible and cost-effective for testing olfactory behaviour in zebrafish.