A fast multichannel fluorometer for investigating aquatic chemoreception and odor trails

An instrument used in measuring the dispersal of fluorescent dye as a tracer of semiochemicals in an aquatic environment allows measurements of chemical gradients to be made over distances naturally separating the bilateral olfactory appendages of small benthic organisms. Its four probes consist of two optical fibers each: one fiber conducts light of excitation wavelengths to illuminate an indicator dye; the other transmits fluorescent emissions from the dye to photodetectors. Sampling is at intervals as short as 10 ms, which approaches the latencies of animal olfactory and taste receptors. The volume sampled by each probe is presently undefined although measurement of dye concentration is attenuated about 10‐fold within 1 cm distant of a probe tip, i.e. within the range sampled by olfactory organs of small aquatic animals. The device uses neither flow cells nor pumping, and it is able to record stable measurements of fluorescent dye in sunlight and in darkness. Initial field measurements affirm that chemo‐orientation by a small aquatic animal is feasible, but it would probably use phase offset in paired sensors and thus require short‐term memory.