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Retinal pigments, structure and function and behaviour
RETINAL PIGMENTS, STRUCTURE FUNCTION AND BEHAVIOUR
Three of the points brought out in the series of papers by Munz and McFarland (1973. 1975) and McFarland and Munz (1975) in this journal warrant comment with reference to some earlier, related work of which the authors do not seem to have been aware. The first point concerns the occurrence of retinal, (retinene,) only in Corj+aenn hippurus and two species of the genus Cnrart~ studied by them. Another concerns the relationship between visual pigments and retinal structure while the third point deals with the visual pigment and the mode of capturing prey by some fishes. In two notes published in this journal, Ali and Heumann (1970, 1972) give the distribution of vitamins A, and A2 in the retinas of about 80 tropical marine fishes from the Pacific belonging to 55 families. Only four of them did not possess vitamin Ai exclusively. These were: Perrometopon pananmse (Serranidae) with an Ai :A, ratio of 4: 1: Carartx- hippos (Carangidae) with A2 only; Coryphaenu hippurus (Coryphaenidae) and Gerres cinereus (Gerridae) both with a 2: 1 ratio of vitamins Ai and AZ. In a study of visual pigments in some tropical marine fishes. Munz and McFarland (1973) claim that Cor_+aerta hippurus and two species of the genus Caranx did not possess any vitamin A2 related pigment. It is unfortunate that Munz and McFarland did not acknowledge this variance with their results and attempt to provide an explanation in their discussion as to the presence of vitamin AZ in one of the species and one genus studied by them. which had been reported earlier in this journal! In their recent paper (Munz and McFarland, 1975) they suggest that the blue- and red-sensitive components (not rhodopsin) also based on retinal, in Coryphaerra hippurus may be cone pigments and relate this to its having a cone rich retina. Our (Ali and Anctil. 1976) histological observations show that Coryphwa hippurus has an abundance of cones with as many single cones as double cones, and dense inner and ganglion cell layers, thus confirming their observation. An extensive study of the retinas of more than a hundred families (Ali and Anctil, 1976) indicates that many species possessing mixtures of rhodopsin and other blue- and red-sensitive vitamin A, based pigments might also have cone-rich retinas. The third point concerns McFarland and Munz’s (1975) observation that fishes silhouetting prey from below possess a single visual pigment. This is reminiscent of what Ali (1959, p. 982) has shown; viz. that in the Pacific salmon (genus Oncorlr~r~chus)..under scotopic conditions, when only the rods are operating. the fish resorts to a silhouette mode of feeding by staying in the bottom third of the tank. its body at II97
AND
a slight angle with the bottom. locating the prey by its silhouette. then making a dash upwards. capturing it and returning to the bottom. Under photopic conditions when the cones arc functioning (the rods being masked by the retinal epithelinl pigment). it swims about in the aquarium at all depths quickly capturing a prey as it sees it. swallowing one and locating another simultaneously. and feeding rate is at its highest. The salmon has a well developed duplex retina. what Wails (1942) would have called an “arhythmic” one, which is capable of marked retinomotor responses (Ali. 1971). Due to these responses the rods are exposed when the fish is in dim light or in darkness and are masked by ihe retinal epithelial pigment when light intensity is above the cone threshold (Ali and Crouzy, 1968). Photobehavioural responses such as feeding. schooling and migration have been correlated with retinomotor responses (Ali. 1961). Thus. it is indeed not only possible to correlate the mode of feeding (behaviour) with visual pigment content in fishes but also these two aspects with retinal structure and function. I thank Prof. Pierre Couillard and Dr. Walter Heumann for discussions and advice. M. 14. ALI
REFEREZCES Ali M. A. (1959) The
photobehavioral Carl. J. Zoo/.
ocular responses
structure. retinomotor and of juvenile Pacific salmon,
37, 965-996. Ah M. A. (1961) The correlation
of photobehavioral and retinomotor responses in the Pacific salmon. In Proqess in Phorobio/og.v (Edited by Christensen B. C. and Buchmann B.). pp. 415317. Elsevier. Amsterdam. Ah M. A. (1971) Les riponses retinomotrices: caracttres et mtcanismes. Vision Res. Il. 1225-3288. Ali M. A. and Anctil M. (1976) Rerimrs of Fishc?;: ,411 Arhs. Springer, Heidelberg (in press). Ali M. A. and Crouzy R. (1968) Action spectrum and ouantal thresholds of -retinomotor responses in the brook trout. Salrrlirnrs fbmirdis (Mitchill) Z. rcwl. ._ Phtxiol. 59. 86-89. Ali M. A. and Heumann W. R. (1970) Distribution of vitamins A, and A2 in the retinas of some marine fishes from the Gulf of California. K.+vI Rr.t IO, 1307-1310. Ali M. A. and Heumann W. R. (1973) Distribution of vitamins A, and A2 in the retinas or some marine fishes from the Gulf of California II. I’kiort Rr\. 12. 21 57-3159.
119s
Letter
to the EdItor
McFarland W. N. and Munz F. W. (19751 Part 111: the evolution of photopic \~sual pigments in fishes. I’isio~ Res. 15, 1071-1080. Munz F. W. and McFarland W. N. (1973) The significance of spectral position in the rhodopsins of tropical marine fishes. L.i.siort Rrs. 13. 1829-1871.
Munz F. W. and McFarland iv. N. (19751 Part I’ prc,umpttve cone pigments extracted from tropIca marine hsheb i.ision Rex 15. 1045-1062. Walls C. L. (1942) The vertebrate eke and Its a~,tptl~c radiation. Cwnhrook Inst. Sci. Bull. 19. ?Sj pp
Three of the points brought out in the series of papers by Munz and McFarland (1973. 1975) and McFarland and Munz (1975) in this journal warrant comment with reference to some earlier, related work of which the authors do not seem to have been aware. The first point concerns the occurrence of retinal, (retinene,) only in Corj+aenn hippurus and two species of the genus Cnrart~ studied by them. Another concerns the relationship between visual pigments and retinal structure while the third point deals with the visual pigment and the mode of capturing prey by some fishes. In two notes published in this journal, Ali and Heumann (1970, 1972) give the distribution of vitamins A, and A2 in the retinas of about 80 tropical marine fishes from the Pacific belonging to 55 families. Only four of them did not possess vitamin Ai exclusively. These were: Perrometopon pananmse (Serranidae) with an Ai :A, ratio of 4: 1: Carartx- hippos (Carangidae) with A2 only; Coryphaenu hippurus (Coryphaenidae) and Gerres cinereus (Gerridae) both with a 2: 1 ratio of vitamins Ai and AZ. In a study of visual pigments in some tropical marine fishes. Munz and McFarland (1973) claim that Cor_+aerta hippurus and two species of the genus Caranx did not possess any vitamin A2 related pigment. It is unfortunate that Munz and McFarland did not acknowledge this variance with their results and attempt to provide an explanation in their discussion as to the presence of vitamin AZ in one of the species and one genus studied by them. which had been reported earlier in this journal! In their recent paper (Munz and McFarland, 1975) they suggest that the blue- and red-sensitive components (not rhodopsin) also based on retinal, in Coryphaerra hippurus may be cone pigments and relate this to its having a cone rich retina. Our (Ali and Anctil. 1976) histological observations show that Coryphwa hippurus has an abundance of cones with as many single cones as double cones, and dense inner and ganglion cell layers, thus confirming their observation. An extensive study of the retinas of more than a hundred families (Ali and Anctil, 1976) indicates that many species possessing mixtures of rhodopsin and other blue- and red-sensitive vitamin A, based pigments might also have cone-rich retinas. The third point concerns McFarland and Munz’s (1975) observation that fishes silhouetting prey from below possess a single visual pigment. This is reminiscent of what Ali (1959, p. 982) has shown; viz. that in the Pacific salmon (genus Oncorlr~r~chus)..under scotopic conditions, when only the rods are operating. the fish resorts to a silhouette mode of feeding by staying in the bottom third of the tank. its body at II97
AND
a slight angle with the bottom. locating the prey by its silhouette. then making a dash upwards. capturing it and returning to the bottom. Under photopic conditions when the cones arc functioning (the rods being masked by the retinal epithelinl pigment). it swims about in the aquarium at all depths quickly capturing a prey as it sees it. swallowing one and locating another simultaneously. and feeding rate is at its highest. The salmon has a well developed duplex retina. what Wails (1942) would have called an “arhythmic” one, which is capable of marked retinomotor responses (Ali. 1971). Due to these responses the rods are exposed when the fish is in dim light or in darkness and are masked by ihe retinal epithelial pigment when light intensity is above the cone threshold (Ali and Crouzy, 1968). Photobehavioural responses such as feeding. schooling and migration have been correlated with retinomotor responses (Ali. 1961). Thus. it is indeed not only possible to correlate the mode of feeding (behaviour) with visual pigment content in fishes but also these two aspects with retinal structure and function. I thank Prof. Pierre Couillard and Dr. Walter Heumann for discussions and advice. M. 14. ALI
REFEREZCES Ali M. A. (1959) The
photobehavioral Carl. J. Zoo/.
ocular responses
structure. retinomotor and of juvenile Pacific salmon,
37, 965-996. Ah M. A. (1961) The correlation
of photobehavioral and retinomotor responses in the Pacific salmon. In Proqess in Phorobio/og.v (Edited by Christensen B. C. and Buchmann B.). pp. 415317. Elsevier. Amsterdam. Ah M. A. (1971) Les riponses retinomotrices: caracttres et mtcanismes. Vision Res. Il. 1225-3288. Ali M. A. and Anctil M. (1976) Rerimrs of Fishc?;: ,411 Arhs. Springer, Heidelberg (in press). Ali M. A. and Crouzy R. (1968) Action spectrum and ouantal thresholds of -retinomotor responses in the brook trout. Salrrlirnrs fbmirdis (Mitchill) Z. rcwl. ._ Phtxiol. 59. 86-89. Ali M. A. and Heumann W. R. (1970) Distribution of vitamins A, and A2 in the retinas of some marine fishes from the Gulf of California. K.+vI Rr.t IO, 1307-1310. Ali M. A. and Heumann W. R. (1973) Distribution of vitamins A, and A2 in the retinas or some marine fishes from the Gulf of California II. I’kiort Rr\. 12. 21 57-3159.
119s
Letter
to the EdItor
McFarland W. N. and Munz F. W. (19751 Part 111: the evolution of photopic \~sual pigments in fishes. I’isio~ Res. 15, 1071-1080. Munz F. W. and McFarland W. N. (1973) The significance of spectral position in the rhodopsins of tropical marine fishes. L.i.siort Rrs. 13. 1829-1871.
Munz F. W. and McFarland iv. N. (19751 Part I’ prc,umpttve cone pigments extracted from tropIca marine hsheb i.ision Rex 15. 1045-1062. Walls C. L. (1942) The vertebrate eke and Its a~,tptl~c radiation. Cwnhrook Inst. Sci. Bull. 19. ?Sj pp