Retinal development in larval and juvenile European eel, Anguilla anguilla (L.)

Retinal structure was examined in 50-mm long leptocephalus larvae and in glass eel to elver juvenile stages. Larvae were found to have a single rodlike photoreceptor, while all postmetamorphic stages displayed a duplex retina. Retinal cell densities or ratios were not found to change with ontogeny in juveniles. Maintenance of juveniles in constant light or constant darkness resulted in a significant increase in numbers of rods and a decrease in numbers of inner nuclear layer cells, respectively. Retinomotor responses were present in all juvenile eels examined. The functional significance of retinal structure is discussed in relation to the different habitats occupied by successive life-history stages.