SOME ASPECTS OF PHOTORECEPTION AND VISION IN FISHES
179
elongate in 20 min in darkness (Pergens, 1896; C h i d , 1904). The
movement of pigment and cones in the common sole ( S o h e o h ) ,
exposed to light or darkness, occupies 30 min to 1 hr (Niml, 1961b).
Fuller data are available for young stages of salmon. Expansion of
pigment in the Atlantic salmon (Salmo salar) exposed to light oocupiea
36 to 60 min ; cones retract in 46 to 70 min. In d a r h w pigment and
mnes retract and olongate, respeotively in 45 to 70 rnin (Fig. 3) (Ali et d.,
1961 ; Ali, 1962). Movements are faster in young atages of Paoific salmon
(Oncorhynchwr spp.). I n the dark contraotion of pigment ocoum in 30
to 46 min ; extension in 10 to 20 min. Cones shorten in 16 to 20 min and
Dark- adoprlon
Pigment
o Cones
0 Retinal index
20 t - N
to I I 1 I l t l 3 l * i r I t i
0
10 20 30 40 SO 60 70 1 8 h )
lime (minutes)
FIQ. 3. Changes in thickness of retinal pigment and longth of cones of young Atlantic
aalmon (Sabru, a-ala7) when transferred from light to darkness. Thickneee of layer
of pigment or cones (left) is plotted against time after tranefer to darknem. Retinal
index (right) = thickness of pigment-layer/thicknoss of )igment-layer + thicknws
of cone-layer. (Reproduced with permission from Ali st d., 1961.)
elongate in 36 to 40 min (Ali, 1959). I n some instanoes it has been
shown that movements during exposure to light am completed sooner
than the reverse movements occurring in darkness, e.g. in S d m salar
(Ali et al., 1961). It will also be noticed that the movements of pigment
and cones may take different times to reach completion.
The experiments from which the above information has been drawn
were conducted under widely different conditions of illumination, and
it is of importance to know the relationship between absolute lightintensities and retinomotor changes.
A photometric criterion used in earIy work was the level of illumination at which colours could just be dist.inguished (by the experimenter). At this level the retinal pigment of the bream (Abrumie
13
179
elongate in 20 min in darkness (Pergens, 1896; C h i d , 1904). The
movement of pigment and cones in the common sole ( S o h e o h ) ,
exposed to light or darkness, occupies 30 min to 1 hr (Niml, 1961b).
Fuller data are available for young stages of salmon. Expansion of
pigment in the Atlantic salmon (Salmo salar) exposed to light oocupiea
36 to 60 min ; cones retract in 46 to 70 min. In d a r h w pigment and
mnes retract and olongate, respeotively in 45 to 70 rnin (Fig. 3) (Ali et d.,
1961 ; Ali, 1962). Movements are faster in young atages of Paoific salmon
(Oncorhynchwr spp.). I n the dark contraotion of pigment ocoum in 30
to 46 min ; extension in 10 to 20 min. Cones shorten in 16 to 20 min and
Dark- adoprlon
Pigment
o Cones
0 Retinal index
20 t - N
to I I 1 I l t l 3 l * i r I t i
0
10 20 30 40 SO 60 70 1 8 h )
lime (minutes)
FIQ. 3. Changes in thickness of retinal pigment and longth of cones of young Atlantic
aalmon (Sabru, a-ala7) when transferred from light to darkness. Thickneee of layer
of pigment or cones (left) is plotted against time after tranefer to darknem. Retinal
index (right) = thickness of pigment-layer/thicknoss of )igment-layer + thicknws
of cone-layer. (Reproduced with permission from Ali st d., 1961.)
elongate in 36 to 40 min (Ali, 1959). I n some instanoes it has been
shown that movements during exposure to light am completed sooner
than the reverse movements occurring in darkness, e.g. in S d m salar
(Ali et al., 1961). It will also be noticed that the movements of pigment
and cones may take different times to reach completion.
The experiments from which the above information has been drawn
were conducted under widely different conditions of illumination, and
it is of importance to know the relationship between absolute lightintensities and retinomotor changes.
A photometric criterion used in earIy work was the level of illumination at which colours could just be dist.inguished (by the experimenter). At this level the retinal pigment of the bream (Abrumie
13