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Open Access Research article

Developmental dynamics of cone photoreceptors in the eel

Phillippa B Cottrill1, Wayne L Davies12, Ma'ayan Semo1, James K Bowmaker1, David M Hunt1 and Glen Jeffery1*

Author Affiliations

1 UCL Institute of Ophthalmology, 11-43 Bath Street, London, EC1V 9EL, UK

2 Nuffield Laboratory of Ophthalmology, University of Oxford, Level 5-6, West Wing, John Radcliffe Hospital, Headley Way, Oxford, OX3 9DU, UK

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BMC Developmental Biology 2009, 9:71  doi:10.1186/1471-213X-9-71

Published: 21 December 2009



Many fish alter their expressed visual pigments during development. The number of retinal opsins expressed and their type is normally related to the environment in which they live. Eels are known to change the expression of their rod opsins as they mature, but might they also change the expression of their cone opsins?


The Rh2 and Sws2 opsin sequences from the European Eel were isolated, sequenced and expressed in vitro for an accurate measurement of their λmax values. In situ hybridisation revealed that glass eels express only rh2 opsin in their cone photoreceptors, while larger yellow eels continue to express rh2 opsin in the majority of their cones, but also have <5% of cones which express sws2 opsin. Silver eels showed the same expression pattern as the larger yellow eels. This observation was confirmed by qPCR (quantitative polymerase chain reaction).


Larger yellow and silver European eels express two different cone opsins, rh2 and sws2. This work demonstrates that only the Rh2 cone opsin is present in younger fish (smaller yellow and glass), the sws2 opsin being expressed additionally only by older fish and only in <5% of cone cells.