The light environments of the ocean are extremely varied, from the colourful shallows of a tropical reef, to the monochromatic twilight of the mesopelagic zone, to the profound darkness of the bathypelagic deep. Near the surface, where light is plentiful, the eyes of fishes are sharply resolved, fast and able to see colour. At greater depths many fishes sacrifice colour and resolution to improve sensitivity for the dim extended scene around them. In contrast, fishes that depend on seeing bioluminescent points of light – ever more visible at greater depths – do the opposite, and have evolved eyes that are highly resolved [1]. Even though some deep-living fishes like the escolar have sacrificed visual speed in favour of sensitivity, others, like the swordfish, have done the reverse. Swordfishes, fast swimming predators in very deep water, have evolved a sophisticated retinal heating system that speeds up vision in order to allow them to better track their fast-swimming prey [2]. Exactly which visual adaptations evolve reflects the habitat and lifestyle of the species in question. In fact, much can be discovered about the lifestyles of little-known fishes by studying their visual adaptations, the central thesis of my review lecture.

REFERENCES

Warrant, E.J. 2000. The eyes of deep-sea fishes and the changing nature of visual scenes with depth. Philosophical Transactions of the Royal Society of London B 355,1155 – 1159.

Fritsches, K., Brill, R. & Warrant, E.J. 2005. Warm eyes provide superior vision in swordfishes. Current Biology 15, 55-58.