Instroduction
During growth, microalgae are able to synthetize high value compounds, such as pigments and polyunsaturated fatty acids (PUFA) giving them significant potential for nutritional purposes, e.g. in aquaculture. For aquafeed preparation the most important fatty acids are linoleic acid (LA; C18:2 , n6), α-linoleic acid (ALA; C18:3 , n3), arachidonic acid (AA; C20:4 , n6), eicosapentaenoic acid (EPA; C20:5 , n3) or docosahexaenoic acid (DHA; C22:6 , n3) which are essential for fish larvae development (Nogueira et al. 2020) . Pikeperch (Sander lucioperca ) is highly demanded fresh and brackish water fish . Most of pikeperch production currently comes from wild fisheries, but the production in recirculating aquaculture systems (RAS) has been increasing, due to its high market value and fast growth rate in RAS. The s urvival rate of pikeperch larvae is usually low, below 20%, due to unsuitable nutrition. The introduction of some rotifers ( e.g. Brachionus plicatilis) as suitable microalgae feed has been successfully performed , increasing the survival rate of pikeperch and overall physiological conditions (Yanes -Roca et al. 2020). In general, rotifers retain the nutritional composition of their diets . They are, hence, regarded as live- feed capsules for the transfer of crucial nutrients, mainly polyunsaturated fatty acids (20:5, n-3 and 22:6, n
3), to fish larvae. Thus, microalgae with substantial fatty acid profile might be used as a feed for rotifers enhancing the rearing successfulness of pikeperch in RAS.
Material and methods
Five different microalgae strains, either Chlorophyceae or Eustigmatophyceae (Chlorella vulgaris, Monoraphidium sp ., Trachydiscus minutus , Vischeria helvetica and Monodopsis sp .) were cultivated in a novel, short light path, annular column photobioreactior (AC-PBR) with internal LED illumination and full control of cultivation variables . The annular interspace (photostage ) for microalgae culturing was only 4.6 cm thick and the highest PAR light intensity that could be achieved was 1600 µmol photons m-2 s-1. During the cultivation of microalgae diets, the physiological stat us was monitored by several Chl fluorescence techniques. The effect of cultivation conditions on t he fatty acid profile was investigated. The microalgae cultures produced in AC-PBR were used for rotifer (Brachionus plicantilis ) feeding. T hese were introduced to pikeperch larviculture in RAS as live feed and the effect on overall fitness of larvae was studied.
Results
All microalgae cultures revealed high photosynthetic activity during the trial due to precious adjustment of required cultivation conditions and reached biomass density up to about 5 g DW L-1 . Under continuous illumination the volumetric productivity was found to be about 0.3 g DW L1 d1 during trials , corresponding to the areal productivity of about 15 g DW m-2 d-1 . B ased on effective cooling, the temperature of cultures could be kept at the optimum value, potentially down to 10 °C within the trial. The proposed model of AC-PBR could even be placed outdoors to further increase cell irradiance for even higher biomass productivity in dense cultures.
Keywords:
m icroalgae, aquaculture feed, diet enrichment , annular column photobioreactor
References:
Nogueira N, Nascimento FJA, Cunha C, Cordeiro N (2020) Nannochloropsis gaditana grown outdoors in annular photobioreactors: Operation strategies. Algal Res 48:101913.
Yanes-Roca C , Holzer A, Mráz J, Veselý L, Malinovskyi O, Policar T (2020) Improvements on Live Feed Enrichments for Pikeperch (Sander lucioperca) Larval Culture. Animals 10, 401.