Light, and photoreceptor degeneration in the Norway lobster, Nephrops norvegicus (L.)

Abstract

The visual pigment of Nephrops norvegicus (L.), the Norway lobster, was measured microspectrophotometrically in isolated rhabdoms, and found to have a $\lambda _{\max}$ at 498 nm. On exposure to light this pigment changed into a long-lived photoproduct of $\lambda _{\max}$ 484 nm (and higher maximal extinction) which broke down slowly in the dark. The bleaching process affected the structural stability of the rhabdoms, resulting in their progressive degeneration. These in vitro effects were found to occur also in vivo by exposing lobsters, caught and maintained in darkness, to low-level illumination from a single fluorescent tube. Exposure of only 2.5 h duration was enough to cause complete degeneration of the rhabdoms within 24 h even though the animals were thereafter kept in darkness. It is suggested that this effect of light is a consequence of the rapid build-up of photoproduct in a species having a low regeneration rate of the visual pigment. When the major part of the visual pigment is in the thermally less-stable, bleached state, the structural integrity of the photoreceptor is affected, leading to degeneration. This type of degeneration might be induced in other 'dim light' species (e.g. deep-sea fishes) that may also have low rates of pigment regeneration.