The effects of replacing fishmeal by Chlorella vulgaris and fish oil by Schizochytrium sp. and Microchloropsis gaditana blend on growth performance, feed efficiency, muscle fatty acid composition and liver histology of gilthead seabream (Sparus aurata)

Abstract

The present study evaluated the effects of replacing fishmeal protein by Chlorella vulgaris meal and fish oil by a blend of Schizochytrium sp. and Microchloropsis gaditana on growth, feed utilization, muscle fatty acid composition and liver histology of Sparus aurata. Fish were fed twice a day for 12 weeks, six isonitrogenous (52% CP) and isoenergetic (21 MJ/Kg) diets at which fishmeal protein of the Control diet was replaced by C. vulgaris meal at 10% (CM10), 20% (CM20) and 30% (CM30) and fish oil of the control diet was replaced by a blend of Schizochytrium sp. and Microchloropsis sp. at 50% (SM50) and 100% (SM100). It was found that the partial replacement of fishmeal protein by C. vulgaris meal up to 30% and the total fish oil replacement by Schizochytrium sp. and M. gaditana blend did not exert any adverse effects on the feed intake, SGR, FCR and PER of fish. Graded levels of C. vulgaris led to an increased lipid retention and deposition mainly in the liver, but no other diet-dependent changes were observed in the whole body and muscle proximate compositions of fish. Microalgae-based diets displayed no major hepatic histomorphological effects, but the very few incidences of hydropic degeneration and haemorrhage that were observed call for further investigation to reveal any potential histopathological impacts of such dietary strategy. Fishmeal replacement by C. vulgaris increased the levels of 18:2n-6 and 18:3n-3 in fish muscle, while EPA and DHA levels were not significantly reduced since dietary fish oil maintained their deposition. Fish oil replacement by the blend of Schizochytrium sp. and Microchloropsis sp. increased the n-6 PUFA and particularly 20:4n-6 and 22:5n-6 in the muscle, while maintained similar EPA and DHA levels compared to the Control group. The present study suggests that the blend of dried biomasses of Schizochytrium sp. and M. gaditana could totally replace dietary fish oil in fishmeal-based diets formulated with soybean oil, without negatively affecting the growth performance, feed efficiency, proximate composition and muscle EPA and DHA levels of S. aurata, even if this resulted in a few histomorphological alterations. Moreover, replacing fishmeal protein by C. vulgaris meal up to 30% that was the maximum level tested did not adversely affect growth performance and feed utilization, even if it resulted in increased lipid retention and deposition in the liver.