Eye lens growth in teleost and elasmobranch fishes

In recent years the vertebrate eye lens has received considerable attention as a potential biochemical recorder and as a source of age information. The vertebrate eye lens grows incrementally, is metabolically inert and mammalian research shows that the inner most part of the eye lens (the eye lens core) is formed during prenatal development and thus contains proteins synthesized around the time of birth. These features have allowed for bomb radiocarbon dating of the eye lens core in mammals. Based on the mammalian studies, it is widely assumed that the eye lens core is formed during prenatal development and is fixed in size at birth in all vertebrate species. Although no previous research has confirmed this for fish species, eye lens core bomb radiocarbon dating as well as results from elemental and isotopic composition studies assuming a fixed lens core size have been reported. In this study, we tested the assumption that the fish eye lens core is fixed in size at hatch and does not grow incrementally thereafter. The assumption was tested by examining the relationship between fish length and eye lens core diameter in four fish species, both teleost and elasmobranch. Our results show that the eye lens core in fish species does not represent a fixed period of growth and can thus not be used for radiocarbon dating nor to account for stock ID and spawning origins via stable isotope analyses