Development of a new index to evaluate zooplanktons' gonads: An approach based on a suitable combination of deformable models

Abstract

Acartia tonsa was used as model to establish an index for oocyte maturity determination in zooplankters based in citometry and histochemical evaluation of gonadic masses. Biometry was performed using an ocular micrometer and nucleus/cytoplasm ratios were obtained characterizing each of the three identified stages: Immature, Vitellogenic and Mature. This paper presents a novel approach since it joins (and, indeed, reinforces) the index framework with the evaluation of the same biological samples by a suitable combination of deformable models. Nucleus contour is identified through Active Shape Models techniques, and cytoplasm contour's detected through parametric Snakes, with prior image preprocessing based on statistical and mathematical morphology techniques. Morphometric parameters such as nucleus and cytoplasm area and ratio between them are then easily computed. As a result the dataset validated the applied methodology with a realistic background and a new, more accurate and ecologically realistic index for oocyte staging emerged. © Springer-Verlag Berlin Heidelberg 2005.