Assessing sensing techniques for detecting markers of approaching ecdysis in juvenile tropical rock lobsters, Panulirus ornatus

Abstract

The development of hatchery technology for spiny lobsters has promoted interest in the establishment of a commercial on shore lobster aquaculture industry in Australia. Cannibalism in culture is extensive with cannibalistic interactions occurring during a relatively brief vulnerability while moulting. Therefore, pre-ecdysis characterisation would create an opportunity to intervene and disrupt cannibalism. Detecting pre-ecdysis with a sensor would open the scope of research into cannibalism reducing culture environments. During this study, three markers that have the potential to indicate ecdysis are assessed: growth of the new integument, formation of suture lines, and pigment changes. These markers were assessed using high frequency imaging ultrasound, computer vision, and digital image analysis in the HSV colour space, respectively.

For individual animals, carotenoid pigment shift is an early and clear marker of pre-ecdysis, however variability between individuals excludes pigmentation being useful in characterising pre-ecdysis. Suture line definition was problematic under visible light because its definition was reduced by similarly coloured pigments, therefore using suture lines as a pre-ecdysis characteriser requires better definition. A logical research approach to enhance suture line clarity in images is to image them with light outside the visible spectrum. Growth of the new integument was visible on sonographs beneath the branchiostegites indicating that ultrasound may be a useful tool for sensing pre-ecdysis in lobsters. Ultrasonic investigation using a single element transducer may be a lower cost and robust sensing solution to detect new integument growth and is a high priority future research pathway.