. Comparative animal physiology. Physiology, Comparative; Physiology, Comparative. Photoreception 413 water but spend the greatest part of their adult Hfe in the ocean (, anad- romous fishes), revealed that thev possess both rhodopsin and porphvropsin, the latter predominating. This predominance of porphvropsin is further exemplified by the brook trout, which can enter the ocean but rarely does so, and the anadromous white perch, which has only the porphvropsin system (Figure 121). Examination of the fresh-water eel, which spawns in the ocean but spends the greatest part of its adult life
. Comparative animal physiology. Physiology, Comparative; Physiology, Comparative. Photoreception 413 water but spend the greatest part of their adult Hfe in the ocean (, anad- romous fishes), revealed that thev possess both rhodopsin and porphvropsin, the latter predominating. This predominance of porphvropsin is further exemplified by the brook trout, which can enter the ocean but rarely does so, and the anadromous white perch, which has only the porphvropsin system (Figure 121). Examination of the fresh-water eel, which spawns in the ocean but spends the greatest part of its adult life in fresh water (, a ca- tadromous fish), revealed that, although it possesses both pigments, rhodop- sin dominates (Fig. 121). The killifish, which spends its entire life in brackish water, is intermediate between the eel and the brook trout. The alewife, an anadromous fish, spends almost all of its life in the sea and vet has only porphyropsin in its retina. In general, it may be said that eury- haline fishes possess predominately or exclusively that photosensitive pigment associated with their spawning environment, , rhodopsin for marine and porphyropsin for fresh-water environment. Since the fresh-water fishes are believed to have a major place in verte- brate evolution, it was of interest to examine the photopigments of other ver- tebrates in the evolutionary line. The cyclostomes are the only living primi- T. WaY9fengt/t Fig. 121. Absorption spectra of retinal extracts from various fishes, showing the tran- sition from the rhodopsin to the porphyropsin system. The dogfish possesses rhodopsin alone; the anadromous white perch possesses porphyropsin alone, and the other species are intermediate. From Wald.^*" tive vertebrates which have eyes sufficiently well developed to permit analysis of photopigments. The sea lamprey, Petromyzon niarinus, an anadromous lamprey, possesses a great preponderance of porphyropsin. Retinas of the lungfish, Protoptenis, have been f
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