Abstract
Microalgae have been used as live food in aquatic species. In recent years, the interest in microalgae has considerably increased, thanks to the evolution of production techniques that have identified them as an ecologically attractive aquafeed ingredient. The present study provides the first data about the effects of dietary inclusion of a microalgae consortium grown in a high-rate algal pond system on zootechnical performance, morphometric indices, and dietary nutrient digestibility as well as morphology and functionality of the digestive system of European sea bass, Dicentrarchus labrax. A dietary treatment including a commercial mono-cultured microalgae (Nannochloropsis sp.) biomass was used for comparison. Six hundred and thirty-six European sea bass juveniles (18 ± 0.28 g) were randomly allotted into 12 experimental groups and fed 4 different diets for 10 weeks: a control diet based on fish meal, fish oil, and plant protein sources; a diet including 10% of Nannochloropsis spp. biomass (100 g/kg diet); and two diets including two levels (10% and 20%) of the microalgal consortium (100 and 200 g/kg diet). Even at the highest dietary inclusion level, the microalgal consortium (200 g/kg diet) did not affect feed palatability and fish growth performance. A significant decrease in the apparent digestibility of dry matter, protein, and energy was observed in diets including 10 and 20% of the microalgal consortium, but all fish exhibited a well-preserved intestinal histomorphology. Moreover, dietary inclusion with the microalgal consortium significantly increased the enzymatic activity of maltase, sucrase-isomaltase, and ɤ-glutamil transpeptidase in the distal intestine of the treated European sea bass. Algal consortium grown using fish farm effluents represents an attempt to enhance the utilization of natural biomasses in aquafeeds when used at 10 % as substitute of vegetable ingredients in diet for European sea bass.
Highlights
Aquaculture plays a key role in supporting human nutrition (Olsen 2011), and the increased availability of raw materials for feed formulation is required to support its rapid and continuous growth
The consortium was characterized by 2.8% nitrogen and 3.2% total lipid
Different microalgae species such as Gracilaria gracilis, Nannochloropsis oceanica, Tisochrisis lutea, and Tetraselmis suecica have been used as partial replacement of fish meal in diets for European sea bass with no adverse effects on zootechnical performance and intestinal physiology (Cardinaletti et al 2018; Messina et al 2019; Valente et al 2019; Batista et al 2020a)
Summary
Aquaculture plays a key role in supporting human nutrition (Olsen 2011), and the increased availability of raw materials for feed formulation is required to support its rapid and continuous growth. Management of sustainable feeding practices for aquatic organisms involves, both from a technical and an economic point of view, identifying alternative resources that consider the nutritional profile and the effects on animal welfare (resistance to stress and disease), while preserving the nutritional quality of the seafood product It implies the management of livestock activities waste into the environment (FAO 2018). The use of microalgae as a potential ingredient of aquafeeds could represent an ecologically attractive alternative to traditional ingredients of marine and plant origin (Becker 2007) and to innovative ingredients such as insects, seaweeds, and yeasts In addition to their basic nutritional value (Spolaore et al 2006), the inclusion of microalgae in aquafeeds is becoming popular as feed supplements in the aquaculture sector (Chu 2012; Priyadarshani and Rath 2012), thanks to the functional properties of their pigments and bioactive compounds. Castro et al (2020) have proved that the inclusion up to 15 % of Nannochloropsis sp. in diets for European sea bass has decreasing effects on the liver and intestinal antioxidant activity, while Abdelghany et al (2020) have demonstrated that dietary N. oculata significantly improves growth parameters and resistance to pathogens such as Aeromonas veronii in Nile tilapia (O. niloticus)
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