Loss of negative eye-size allometry in a population of Aplochiton zebra (Teleostei: Galaxiidae) from the Falkland Islands

Abstract

The population of zebra trout (Aplochiton zebra – Galaxiidae) in Red Pond, Falkland Islands, lacks the negative eye size allometry that is typical of the species elsewhere. Eye size retains a near constant relationship to head length throughout growth in Red Pond. In addition, the bold, narrow, vertical, zebra-like, dark bands typically found on the body of this species are lacking, or are present in the Red Pond population only as broader dusky blotches. Absence of negative allometry is probably due to lack of coupling of eye and somatic growth, probably owing to slow growth of the fish living in the challenging dietary environment of a turbid lake. Observations of diet show that the species is a generalised invertebrate carnivore, but that food intake may be low, suggesting that the modified coupling of eye growth to somatic growth is a likely explanation of the loss of negative allometry.