Inclusion of photoautotrophic cultivated diatom biomass in salmon feed can deter lice

Abstract

The aim of this study was to evaluate the potential of diatom (microalgae) biomass as a lice-reducing ingredient in salmon feed. The original hypothesis was based on the fact that polyunsaturated aldehydes (PUAs), e.g. 2-trans, 4-trans decadenial (A3) produced by diatoms can function as grazing deterrents and harm copepod development. Salmon lice (Lepeophtheirus salmonis) is a copepod, and we intended to test if inclusion of diatom biomass in the feed could reduce the infestation of lice on salmon. We performed experiments where salmon kept in tanks were offered four different diets, i.e. basic feed with diatoms, fish oil, Calanus sp. oil or rapeseed oil added. After a feeding period of 67 days a statistically representative group of fishes, tagged with diet group origin, were pooled in a 4000L tank and exposed to salmon lice copepodites whereafter lice infestation was enumerated. Salmon from all four diet groups had good growth with SGR values from 1.29 to 1.44% day-1 (increase from ca. 130 g to 350 g). At the termination of the experiment the number of lice on salmon offered diatom feed were statistically significantly lower than on salmon fed the other diets. Mean lice infestation values increased from diatom feed through Calanus and fish oil to standard feed with terrestrial plant ingredients. Analysis of the chemical composition of the different diets (fatty acids, amino acids) failed to explain the differences in lice infestation. The only notable result was that diatom and Calanus feed contained more FFA (free fatty acids) than feed with fish oil and the control feed. None of the potential deleterious targeted polyunsaturated aldehydes could be detected in skin samples of the salmon. What was exclusive for salmon that experienced reduced lice was diatom inclusion in the feed. This therefore still indicates the presence of some lice deterring ingredient, either in the feed, or an ingredient can have triggered production of an deterrent in the fish. An obvious follow up of this will be to perform experiments with different degrees of diatom inclusion in the feeds, i.e. dose response experiments combined with targeted PUA analyses, as well as to perform large scale experiments under natural conditions in aquaculture pens.

Mass Cultivation of Microalgae: I. Experiences with Vertical Column Airlift Photobioreactors, Diatoms and CO2 Sequestration

“…Preliminary results indicate the need for large (diatom) production volumes and possibly higher prices justified by environmentally sustainable production processes. The produced biomass has also been tested with success as an ingredient in lice deterring salmon feed [176].…”

Mass Cultivation of Microalgae III: A Philosophical and Economic Exploration of Carbon Capture and Utilization

“…One of the largest problems the salmon industry currently faces is salmon lice (Lepeophtheirus salmonis) infestation [46]. Our produced feed has, as mentioned, lice-deterring abilities [40], and ongoing new experiments have indicated a reduction in lice infestation of up to 50%. A question here is if salmon can digest algae feed without negative consequences on growth, physiology, and health.…”

“…The UiT-Finnfjord AS project has, as mentioned earlier, been described in detail in Eilertsen et al [36,40,48]. The main Finnfjord product, ferrosilicon, is a necessary ingredient in steel production, and Finnfjord is committed to sustainable production and is working to reduce its environmental impact.…”

“…The main project partners are the ferrosilicon factory Finnfjord AS and UiT-The Arctic University of Norway, both situated in the southern part of northern Norway. Thorough descriptions of the project, processes, and data referred to are already published [36,40,48], i.e., this article only focuses on the most important project inventory and cultivation results. The main application of the diatom biomass was from the start fish/salmon feed, this with the alleviation of the lack of marine biomass in the feed as a result.…”

“…The main application of the diatom biomass was from the start fish/salmon feed, this with the alleviation of the lack of marine biomass in the feed as a result. Lately, salmon lice reduction [40] and value-added products such as omega-3 oils, diatom scales and pharmaceuticals have had much focus.…”