(TSVN) – Nutrition experts in the US have invented a kind of feed containing 2 microalgae mixtures that help tilapia farmers save their production cost and improve growth at the same time by eliminating fish meal, fish oil.

The experts from California Santa Cruz University, USA used a mixture of microalgae as feed for tilapia (Orochromis niloticus) and compared it to the control diet that contains fish meal, fish oil. The result showed that microalgae-blend feed can be used to replace fish meal, fish oil and improve growth and economic effectiveness.

Setting up experiment

The experiments included 4 treatments, 3 times repeated in each RAS tank of 480 tilapias (average size 34,5± 2.06g) and were divided into groups of 40 fish/group, weighed the groups and moved into tanks. Tame fish so that they adapt their living environment and industrial feed that contains fish meal and fish oil within 7 days. The recommended initial density to avoid physical stress (<0.25kg/gallon in 80 gallons of RAS tank). Every day, monitor the water quality carefully to maintain suitable conditions for tilapia in all RAS tanks and keep the water temperature at 28.7±0.25 °C, pH 7.1±0.1, dissolved oxygen concentration at 6.1 ± 0.15 mg /liter, total ammonica nitrogen 0.26 ± 0.1mg /liter and nitrite nitrogen 0.3 ± 0.01mg /liter.

For the experiment of feeding, the experts combined defatted algae biomass of Nannochloropsis oculata (N.oculata) to replace different proportions of fishmeal and whole algae cells of Schizochytrium sp for fish oil in 3 tilapia treatments. The formula of these three treatments based on the data about algal digestibility in the previous research. Compare three treatments to control diet (FMFOC) at a similar rate for commercial feed. All diets were made based on the formulas of iso-nitrogenous (37% crude protein) and iso-energetic (12kJ /gram).

The defatted diets that supplement N.oculata replace fishmeal at the rates of 33% (33NS), 66% (66NS) and 100% (100NS) and the diets using whole microalgae cells Schizochytrium sp to replace all fish oil in experimental diets (33NS, 66NS, 100NS). Therefore, N.oculata microalgae account for 3.5% and 8% in the feed and Schizochytrium sp algae account for 3.2%. Tilapia will be fed twice a day with the feed amount of 8% of its weight until the 60th day; 6% to 121th day and 4% to 183th day.

The biomass of tilapia was measured monthly. The research team selected randomly and weighed 10 tilapia in the experiment and deploy biochemical analysis. 6 samples were taken on the 121st day, and 6 others were taken on the last day of the test (185th day). Half of the fish samples that were taken on the 121th and 185th day were fillet filtered, the remaining was kept intact, then preserved for further processing.

Results and discussion

The experts invented new feed by combining byproducts of protein-rich defatted seaweed N.ocutala (50%) – byproducts after extracting EPA and Schizochytrium sp. algae DHA-rich (30%) to replace all fish meal and fish oil. According to previous reports, microalgae Schizochitrium sp is an easily digestible source of nutrients for tilapia and can completely replace all fish oil in tilapia feed.

The results of the research have proved the feasibility of a combination of microalgae biomass that is available on the market today (Schizochytrium sp. And N. oculata) to create a feed formulation that does not contain marine fish ingredients but still gain efficiency. This is also the first report of a successful combination of these two algae to completely replace fishmeal and fish oil in tilapia formulations.

The combination between Schizochytrium sp. and N.oculata in marine fish-free feed has two main benefits. Firstly, fish achieve steady growth thanks to the digestible algae Schizochytrium sp. Raising the content of algae Schizochytrium sp. also improves growth, FCR, and protein efficiency (PER). Secondly, the protein from the defatted algae biomass N.oculata has the highest digestibility when combining with the microalgae Schizochytrium sp. due to the release of microalgae Schizochytrium sp. and then active digestive enzymes.

The combination of algae N.oculata and Schizochytrium sp. is more suitable for digestive enzymes in the intestine of fish than traditional foods containing fishmeal and fish oil. Algae Schizochytrium sp. also helps to improve the digestibility of food with a higher content of N.oculata. However, it is necessary to study more about the composition of digestive enzymes in various nutritional mechanisms.

Source: thuysanvietnam.com.vn

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