ELECTRORETINOGRAPHIC EVALUATION OF SPECTRAL SENSITIVITY IN YELLOW ANDSILVER EELS (ANGUILLA-ANGUILLA)

Although differences in visual pigments between developmental stages o f the European eel are well known, the expected differences in spectra l sensitivity have not been demonstrated at the electrophysiological l evel. In fact, one past electroretinographic study led to the conclusi on that in eels there is no change in scotopic sensitivity, with incre asing sexual maturity. In the present experiments, electroretinograms (ERGs) were recorded from in situ eyecups of immobilized eels Anguilla anguilla (L.) caught in coastal running waters. It was shown that the ERG b-wave is as good an indicator of spectral sensitivity as the unm asked late receptor potential (LRP) which directly reflects the respon siveness of photoreceptors. Complete spectral-sensitivity curves, base d on b-wave thresholds and on thresholds of LRP subsequently isolated by means of sodium iodate, have been obtained in the same eel. Using f itted amplitude-log intensity functions for threshold calculation, and two models for computer-assisted fitting of spectral-sensitivity curv es, significant differences in lambda(max) were found between yellow a nd silver developmental stages of the eel, identified by ocular index measurements.