Visual Thresholds and Spectral Sensitivity of Herring Larvae

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Abstract
1. Herring larvae are characterized by eyes with no rods and no retinomotor responses, though both are present in the adult. 2. By observing the extinction of phototactic behaviour and feeding in herring larvae of different ages held at low intensities of white and coloured light, it was possible to obtain a measure of both threshold light intensities and spectral sensitivity for a pure-cone eye. 3. The phototaxis was positive at higher intensities, the threshold being 100 to 10-1 m.c. Below this threshold a negative phototaxis was observed which disappeared at a much lower threshold, about 10-5 to 10-6 m.c. The threshold for feeding varied with age and the type of food organism, lying between 10-1 and 10-2 m.c. 4. The high sensitivity for negative phototaxis was probably a visual response and not one mediated by a dermal light sense. 5. Spectral sensitivity varied depending on age and behavioural criteria. Using feeding and positive phototaxis the action spectrum was broad and plateau-like with a maximum in the yellow-green and would appear to be similar to other photopic curves. The action spectra for negative phototaxis showed a number of peaks. At hatching three peaks at 450, 520 and 600 mµ might represent three types of cone as postulated by the Young-Helmholtz theory of colour vision.

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