J Comp Physiot A (1988) 162:543-550 Jm.m~l eli Neural, and Physiology A .."e=,% a', 9 Springer-Verlag 1988 Visual pigments in the individual rods of deep-sea fishes J. C. Partridge, S.N. Archer, and J.N. Lythgoe Department of Zoology, University of Bristol, Woodland Road, Bristol, BS8 lUG, United Kingdom Accepted October 8, 1987 Summary. The visual pigments in the rods of 15 species of deep-sea fish were examined by mi- crospectrophotometry. In 13 species a single visual pigment was found. The 2max of these pigments, which ranged from 475 nm to 488 nm, suggest they give the fish maximum sensitivity to the ambient light in the deep, blue ocean waters where they live. In two species two visual pigments were found in separate rods. Bathylagus bericoides had rho- dopsins of 2max 466 nm and 500 nm and Malaco- cephalus laevis had two rhodopsins of 2max 478 nm and 485 nm. It is noted that the species with two visual pigments tend to be dark in colour and live in deeper, darker, water. In most deep-sea fishes partial bleaching exper- iments have shown that a single retina contains only one visual pigment and because most of these fishes have pure rod retinae (All and Anctil 1976), it is reasonable to think that all the rods contain the same visual pigment. However, it will be seen from Table 1 that in a few fishes there is more than one visual pigment present and the question arises whether individual rods contain a mixture of visual pigments, or whether the pigments are contained in separate rods. The technique of mi- crospectrophotometry (MSP) has enabled us to an- swer this question, and we report here that individ- ual rods do contain different visual pigments. Introduction The average depth of the oceans is 3800 m (Her- ring and Clarke 1971), yet daylight becomes too dim for fish to see it at a quarter of that depth (Clarke 1936). This is true for even the most sensi- tive fish looking directly upwards in the clearest ocean water on the brightest tropical day (Clarke and Denton 1962; Dartnall 1975). Beneath 1000 m and at night there is visible light but it is provided by the animals themselves rather than by the sun. The clear water of the open ocean is most trans- parent to blue light and below about 100 m the daylight available for vision is restricted to a wave- band between about 450 and 500 nm (Dartnall 1975). In 1936 Bayliss et al., and Clarke (1936) pre- dicted that the visual pigments of deep-sea fishes would be those that absorb most strongly in this region of the spectrum, and their prediction has been confirmed by several studies on the visual pigments extracted from whole retinae (for refer- ences see Table 1). Material and methods Fish were collected by deep water trawling from the R.R.S. Challenger (Cruise number 6, October 1986). Trawling was con- ducted to the south of Madeira in a triangular area approxi- mately defined by the points 32~ 17~ 32~ 17~ and 32~ 17~ The fishing technique and the design of the RMT50 midwater trawl are described by Clarke and Pascoe (1985). The depth of trawling varied between 600 and 1200 m but since the trawl was not of the closing type it is possible that some of the fish were caught at shallower depths. Fish were selected from hauls that were brought on deck at night. The catch was shielded from deck lights as much as possible and was inspected with a torch fitted with a red filter. Fish that were alive or appeared to be undamaged were quickly transferred to a light-tight container containing iced sea water. In a darkroom fish were decapitated if live, enucleated and the retinae removed under near infra-red light (Kodak Wratten filter No. 87c over a tungsten light source) with the aid of an infra-red image converter (FJW Industries, Mt. Prospect, Illinois) attached to one ocular of a low power stereomicros- cope. Retinae were washed in calcium-free, phosphate buffered saline (PBS, Dulbecco 'A' diluted to 425 mOsm/1, pH 7.3, Ox- old Ltd., Basingstoke UK). The tissue was lightly fixed by being gently agitated for 5-20 s in a solution of 5% glutaraldehyde in 0.1 M phosphate buffer (pH 7.4) with 0.3 M sucrose, washed