Introduction
Aquaculture production is in continuous growth both for macroalgae species and fed fish species, like Atlantic salmon (Salmo salar) (FAO, 2020). The growth of fed fish species calls for novel feed resources to enable this growth, and in this regard, algae have been recognized as having promising potential relating to their nutritional value, sustainability in production, as well as their biologically active components (Naylor, 2009; Wan et al., 2019; Albreksten et al.,2022). However, the expected effects will depend on the species being fed, and the algae species in question.
The red seaweed species Palmaria palmata has been suggested as a feed additive candidate, mainly due to its high protein content and bioactive components that could have positive impacts on fish health (Florence, 1999; Holdt & Kraan, 2011;Grote et al., 2019). Wan et al. (2016) used different inclusions of P. palmata in feed for Atlantic salmon during the last feeding phase before slaughter, finding no difference in growth between algae-fed and control groups. This indicates the possibility of also using algae as a feed ingredient for carnivorous fish. However, the effects of such supplements in early feeding stages is yet to be determined. The fish are sensitive to environmental impact in the early phase (Lowe, 2021), suggesting that potential positive or negative effects from different factors like feed can be expected to be magnified. This study characterizes the effects of using a red algae (Palmaria palmata) as feed supplementation during the start feeding period of Atlantic salmon (Salmo salar) and discuss this potential use of this algae biomass.
Materials and methods
A 4-month start feeding trial was conducted by feeding tanks of Atlantic salmon fry up till an average weight of 10 grams. The algae used in the trial was sourced locally from the Trondheimsfjord shore (Storsteinan) during September. It was rinced, freeze dried and ground into a powder for feed production.
Triplicate groups were fed with control and algae supplemented (5% dried P. palmata) diet from start feeding until an average weight of 5 grams, then a standard feed without supplementation until the end weight of 10 grams. This enabled a comparison of which effects relate to the algae diet, and whether these would be sustained after a diet change. Sampling of tissue from liver and intestines were performed at average individual fish weights of 0.4, 1, 5 and 10 grams, and samples were used to assess growth, intestinal development and health, and microbiological flora.
Results and discussion
Preliminary results indicate no negative effects on growth from the algae addition to the diet, with a higher average end weight for the algae fed group (10.4±3.1 gram±SD) but no significant difference from the control group (10.2±2.9 gram±SD). There was a non-significant higher survival rate in the Palmaria-fed group. These results give a preliminary indication that the red algae supplement does not have a harmful effect on the growth and survival of salmon fry.
Most samples, including tissue for histological and microbiological analysis, are still being processed. Results from this will be included in the amended abstract.
Further discussions and results will be added to the amended abstract.
Conclusion
The study’s initial conclusion is that the use of red algae as a feed supplement can give equal growth as commercial feeds used today.
Further conclusions will be included with the amended abstract.
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