Effect on the growth and body composition of juvenile tilapia Oreochromis niloticus fed raw Spirulina

In order to develop a food chain (phytoplankton-fish) in a closed ecological recirculating aquaculture system (CERAS), unialgal cultures of Spirulina platensis were fed to tilapia Oreochromis niloticus (bodyweight; 1.59 ± 0.26 g, standard length; 3.4 ± 0.17 cm) for 9 weeks, using a commercial diet as the control treatment. Water temperature was 28 ± 0.5°C. Juvenile tilapia grew efficiently [specific growth rate (SGR)=3.14, feed efficiency (FE)=1.22] and showed a high survival rate (95%) for the duration of the trial without any nutrient supplements, although the fish fed the commercial diet had a slightly higher growth rate. A proximate composition analysis showed that fish fed Spirulina had a higher protein content, a higher polar lipid content and a lower ash content than fish fed the commercial diet. The abundance of linoleic acid and γ-linolenic acid (GLA) in the Spirulina was reflected in the fatty acid profile of the fish. Σn-6 highly unsaturated fatty acid (20:3n-6, 20:4n-6, 22:4n-6, 22:5n-6), which seemed to be metabolized from linoleic acid and GLA, increased and were more pronounced in the polar lipid fraction. On the contrary, Σn-3 fatty acids, such as α-linolenic acid, eicosapentaenoic acid and docosahexaenoic acid, decreased. No significant differences were observed in the mineral and essential amino acid contents in the fish at the experiment's completion, even though there were some differences between raw Spirulina and the commercial diet. The results suggest that it is feasible to construct a food chain using raw Spirulina to feed transition-stage tilapia in a CERAS.