Use of image analysis software to assess American eel (Anguilla rostrata) elver external pigment development
LE3 .A278 2021
Bachelor of Science
Runs of American eel (A. rostrata) elvers exhibit pronounced variability in body length, body weight and degree of external pigmentation within-season and among-years. These factors are thought to influence the level of recruitment to the standing stock of yellow eels and eventually adult production, and they can potentially influence the value of the landed catch from the commercial fishery. Documentation of within-and among-year variability in these traits is time consuming, susceptible to measurement error both in accuracy and precision and in the case of external pigmentation subject to observer bias in interpretation of categorical criteria. This study evaluates the potential usefulness of image analysis to quantify the development of elver pigmentation as a continuous variable using pixel intensity and to estimate elver lengths. Scanned images of elvers were assessed using ImageJ photo analysis software to quantify the development of elver pigment using pixel intensity of strategically selected areas within the elver body creating a pigment index. The index revealed a sigmoidal progression of body pigmentation with time within-years. Comparison of index values derived from the scanned images are shown to be more informative as a means to assess pigment development with time than are categorical indices in current use. The new index allows for pigment development to be treated as a continuous variable when relating physiological development to biological, ecological, and environmental factors.
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