Online PhD defence by Josefine Holm Nielsen

Title: The feasibility of optical monitoring of larval salmon lice


Principal supervisor: Senior Researcher Peter John Rodrigo, DTU Fotonik
Co-supervisor: Professor Christian Pedersen, DTU Fotonik
Co-supervisor: COO Flemming Bent Rasmussen, FaunaPhotonics ApS 
Co-supervisor: Assoc. Prof. Mikkel Brydegaard, Norsk Elektro Optikk AS, Norway
Co-supervisor: Professor Thomas Kiørboe, DTU Aqua

Evaluation Board
Researcher Anna Solvang Båtnes, Department of Biology, Norwegian University of Science and Technology, Trondheim, Norway
Professor Børge Hamre, Department of Physics and Technology, University of Bergen, Norway 

Professor Paul Michael Petersen, DTU Fotonik, Denmark

Master of the Ceremony
Assoc. Prof. Peter Tidemand-Lichtenberg, DTU Fotonik, Denmark


Salmon lice are parasites living on salmon that pose a persistent challenge to the salmon farming industry, with major economic and environmental implications. Detection of the larval salmon lice could give the salmon farmers an early warning system before the parasites infect the fish, which would improve treatment planning. However, there is a lack of efficient methods for detecting larval salmon lice. In its larval stage, salmon lice live freely in the water. The aim of this thesis is to explore the feasibility of optically detecting them in this stage, and the possibility of distinguishing them from other marine animals (zooplankton) of similar size.

In this thesis, several different optical properties of larval salmon lice have been investigated. A significant difference was observed in the autofluorescence induced by violet laser illumination in salmon lice larvae and other non-parasitic zooplankton. Specifically, it was found that animals eating algae, which are the majority of zooplankton in the relevant size range, exhibited strong red autofluorescence from undigested chlorophyll in the gut. Salmon lice larvae, which does not eat until they attach to a host, did not exhibit this type of fluorescence. All measured species, including salmon lice larvae, exhibited cyan autofluorescence. Based on these results, a prototype optical detector was built to measure cyan and red autofluorescence simultaneously. The cyan autofluorescence is used to detect zooplankton and the red autofluorescence is used to determine if it is a non-eating species, like salmon lice, or an algae-eating species. It was found that it could distinguish salmon lice larvae from algae eating zooplankton more than 94 % of the time in clean water. Finally, the detector was tested in water containing algae and dissolved organic matter, and it was found that this negatively affected the sensitivity of the detector. Future work will explore how to increase the signal in such conditions. 

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ons 03 jun 20
13:30 - 16:30


DTU Fotonik


Online. Please write to Maria Louisa Rosenberg Welling to sign up.