|In this ongoing project, we have sought to determine if the pattern of chromotaphore position and/or the presence of irregularities in the iris of mosquitofish (Gambusia affinis) and juvenile sunfish (Lepomis macrochirus) could be used to identify individual fish. These are small, colorless fish; marking such individuals with one of a variety of widely-used techniques (e.g., subcutaneous paint, eye tags, PIT tags, etc.) can be time-consuming, overly stressful, and/or expensive.
Our approach has been to take close-up digital photographs of lightly anaesthetized fish on two or more different occasions, and then see if we can relaibly re-identify individuals from the arrays of photographs. The project has met with mixed success so far, but I am hopeful that more prgoress will be made in the future.
As examples of this strategy, the photographs below show the kinds of observations we can make. The upper left photo of each set is of the left eye of an individual female mosquitofish; the right photo is the same eye photographed a week or more later. Chromatophore (circles) and iris irregularity (arrows) landmarks that can be used to tie the two pictures to the same fish are indicated (the lower left photo is simply a copy of the upper left photo with landmarks superimposed).