Spirulina (Arthrospira) platensis as a protein source could improve growth, feed utilisation and digestion and physiological status in juvenile blunt snout bream (Megalobrama amblycephala)

To investigate the effects of replacing fishmeal with Spirulina (Arthrospira) platensis, juvenile blunt snout bream (Megalobrama amblycephala) (bodyweight 21.60 +/- 0.44 g) were fed with six diets containing 0%(SP0), 0.75% (SP0.75), 1.5%(SP1.5), 3%(SP3), 6%(SP6), and 9.5%(SP9.5) of S. platensis for 65 days. It was found S. platensis improved growth performance, that the weight gain rate (WGR), protein efficiency ratio (PER) were highest following 3.0% S. platensis, and the feed conversion ratio (FCR) was lowest. Besides, the WGR of SP3 group was significantly higher than SP6 and SP9.5 groups, while the PER and FCR were significantly different from the SP6 group. S. platensis affected the apparent digestibility of crude lipid, which was higher in the SP9.5 group than the control and the SP0.75 groups, but the digestibility of methionine and cysteine were lowest in SP9.5 group. As for the muscle compositions, serine was significantly elevated in the SP1.5 group than the control group, and glycine was significantly increased in the SP3 group. The contents of lysine and valine in whole fish were significantly higher in the SP1.5 group than the SP0.75 group. The content of complement 4 in plasma was significantly lower in control group than the SP1.5-9.5 groups. The plasma aspartate transaminase activities and the malondialdehyde contents of SP6 and SP9.5 groups were significantly higher than the SP1.5 group. The liver peroxidase activity and total antioxidant capacity of SP9.5 group were significantly lower than control group. In summary, the inclusion of S. platensis could improve lipid digestion and immune response of M. amblycephala. 3.0% S. platensis inclusion in the diet (replacing 33.25% fishmeal) achieved the best growth performance and feed utilisation.