THE BEEAVIODR AND PHYSIOLOGY OF HERRING AND OTHER CLITPEIDS 315
rotating action of the eyeball (nystagmus) in herring and an associated
ventral foveal region where the cones were ten times as dense as
elsewhere. No doubt the apparent high acuity of clupeids is an adaptation t o feeding on small plankton organisms. As the light decreases,
rod vision presumably becomes dominant and acuity drops ; later,
behavioix patterns associated with vision cease. Presumably the
threshold light intensity at which such behaviour patterns cease will
vary considerably ; the continuation of feeding, for example, will
depend t o a great extent on the size of the food, but this has not been
worked on.
2. Vision at low light intensities
The threshold light intensity at which various behaviour patterns
cease are discussed under the particular behaviour pattern concerned,
e.g. shoaling, feeding. Protasov et al. (1960), however, using a flicker
fusion frequency technique, found that the transition from day to
“ night ” vision occurred at 1.0-0.1 lux in Engraulis encrasicholus.
3. Spectral sensitivity
Some data are available on the spectral sensitivity of clupeids,
though colour vision has not yet been demonstrated. Borisov and
Protasov ( 1960) showed by electrophysiological techniques that the
‘ I anchovy ” had a spectral sensitivity curve with a maximum at
500 m p . There was a Purkinje shift., the maximum when light adapted
being at 560 mp. Blaxter (unpublished data), by finding the feeding
threshold of young herring in different coloured light, and by other
behaviour techniques, showed there was a maximum sensitivity in the
blue-green, but the curve was plateau-like with a sharp fall off only in
the red. A fairly high sensitivity in the violet suggests that experiments
t o test the reactions of clupeids to ultra-violet light would be worthwhile, though the existence of a positive reaction would depend on
whether the lens would transmit short wavelength light. Fisher
(personal communication) found that retinal pigment extracted from
the eyes of dark-adapted herring had a maximum absorption at 500 mp.
4. Distance vision
A little is known of the distance herring can see. For instance,
Williamson (1917) found in aquaria that food could be seen 30-90 cm
away depending on its size, and Schkfer (1955) that herring could see
1.0-1.5 m. Blaxter et al. (1960) found a reaction distance to nets of
1.5-2.0 m.
rotating action of the eyeball (nystagmus) in herring and an associated
ventral foveal region where the cones were ten times as dense as
elsewhere. No doubt the apparent high acuity of clupeids is an adaptation t o feeding on small plankton organisms. As the light decreases,
rod vision presumably becomes dominant and acuity drops ; later,
behavioix patterns associated with vision cease. Presumably the
threshold light intensity at which such behaviour patterns cease will
vary considerably ; the continuation of feeding, for example, will
depend t o a great extent on the size of the food, but this has not been
worked on.
2. Vision at low light intensities
The threshold light intensity at which various behaviour patterns
cease are discussed under the particular behaviour pattern concerned,
e.g. shoaling, feeding. Protasov et al. (1960), however, using a flicker
fusion frequency technique, found that the transition from day to
“ night ” vision occurred at 1.0-0.1 lux in Engraulis encrasicholus.
3. Spectral sensitivity
Some data are available on the spectral sensitivity of clupeids,
though colour vision has not yet been demonstrated. Borisov and
Protasov ( 1960) showed by electrophysiological techniques that the
‘ I anchovy ” had a spectral sensitivity curve with a maximum at
500 m p . There was a Purkinje shift., the maximum when light adapted
being at 560 mp. Blaxter (unpublished data), by finding the feeding
threshold of young herring in different coloured light, and by other
behaviour techniques, showed there was a maximum sensitivity in the
blue-green, but the curve was plateau-like with a sharp fall off only in
the red. A fairly high sensitivity in the violet suggests that experiments
t o test the reactions of clupeids to ultra-violet light would be worthwhile, though the existence of a positive reaction would depend on
whether the lens would transmit short wavelength light. Fisher
(personal communication) found that retinal pigment extracted from
the eyes of dark-adapted herring had a maximum absorption at 500 mp.
4. Distance vision
A little is known of the distance herring can see. For instance,
Williamson (1917) found in aquaria that food could be seen 30-90 cm
away depending on its size, and Schkfer (1955) that herring could see
1.0-1.5 m. Blaxter et al. (1960) found a reaction distance to nets of
1.5-2.0 m.