Co-culture ofUlvasp. andDicentrarchus labraxin Recirculating Aquaculture System: effects on growth, retention of nutrients and fatty acid profile

Abstract

European sea bass andUlvasp. were co-cultured in different tanks of an indoor Recirculating Aquaculture System (Ulva-RAS) with bacterial biofilter, in an effort to optimize the efficiency of the system and to further decrease the waste effluent. A system with similar culture conditions, withoutUlva,was used as a control-RAS to elucidate integration effects on growth performance and chemical composition of sea bass. The role ofUlvaon N and P concentrations, gas (O2, CO2) and pH in water was also investigated. Fish were fed a diet of fish oil replacement (55%) with a mixture of rapeseed oil and palm oil (1:1). Our data showed thatUlvacould uptake N and P nutrients, but could also enrich sea water with phosphates. Sea bass reared inUlva-RAS exhibited isometric growth, while fish in control-RAS showed a positive allometric growth and an increased variance of body weight and length. In addition, sea bass inUlva-RAS demonstrated significantly higher levels of condition factor (K), feed intake, protein, lipid, P, EPA and DHA content (% wet weight of total body) and lipid productive value, compared to fish in control-RAS.Ulva,after bi-weekly culture, showed increased protein content (60%) compared to wild seaweed collected nearshore. CultivatedUlvaobtained dark green color, doubled chlorophyll concentrations, and exhibited lower levels of saturated and higher levels of certain monounsaturated and n-3 polyunsaturated fatty acids, indicating increased photosynthetic activity. Present results revealed the beneficial effects ofUlvaon sea bass growth and quality, which led to an improved response to the nutritional stress imposed by the fish oil replacement with vegetable oils, thus contributing to a sustainable aquaculture. Moreover, it was concluded thatUlvacould improve water quality by increasing pH and O2, reducing CO2and contribute to bioremediation of ammonia and nitrates from water in integrated aquaculture.