Effect of supplementation of marine microalgae Conticribra weissflogii and Nannochloropsis oceanica on the content of lipids and fatty acids and on the growth of white shrimp Litopenaeus vannamei in biofloc systems (BFT)
Microalgae are of great importance in aquaculture, as they improve water quality and still constitute a good source of nutrients such as lipids, fatty acids, proteins and vitamins. In the biofloc system, water quality is maintained efficiently by bacteria and also by microalgae, which serve as a food supplement for the organisms produced. This work had as general objective to evaluate the supplementation of the marine microalgae Nannochloropsis oceanica and Conticribra weissflogii supplied in culture medium and concentrated (wet and dry) in the production water and in the performance of the white shrimp Litopenaeus vannamei, produced in BFT system. For this, three experiments were carried out with the addition of microalgae. The first 2 experiments differed in terms of the size of the animals (0.014g and 0.70g),but they were composed of the same treatments (with three replications), 1) Control - without the addition of microalgae, 2) TM - with the addition of microalgae in culture medium; 3) TU - with the addition of wet microalgae biomass and 4) TS - with the addition of dry microalgae biomass. In experiment 3, 125 g of wet biomass of the microalgae N. oceanica were added to the treatments: TBM- bioflocs with microalgae, TAM- clear water with microalgae and TBFT- bioflocs, TAC- clear water without microalgae. All with three repetitions. Water quality parameters were monitored, such as temperature, salinity, oxygen, ammonia, nitrite, nitrate, phosphate, pH, alkalinity and SST. For experiments 2 and 3, lipid and fatty acid analyzes were performed. In experiments 1 and 2, there were no significant differences in water quality parameters. In experiment 3,ammonia levels in treatments with clear water were higher than in treatments with bioflocs, while nitrate was higher in treatments with bioflocs. In experiment 1, the final weight was higher in the treatments with moist microalgae and control for C. weissflogii, while there were no significant differences for N. oceanica. In experiment 2, there were no significant differences in the zootechnical performance of the shrimp. For experiment 3, the highest final weight was found in treatments with the addition of microalgae (TBM) and (TAM). In experiment 2, the lipid values in the shrimp muscle did not differ for the two microalgae. The fatty acids C 16:0 and C 18:0 showed higher values in TM of N. oceanica, while for C. weissflogii,the highest values were found for C 20: 4 (TU) and C22: 6 (TM) polyunsaturated fatty acids. In the third experiment, the levels of lipids were higher in the TBM treatment, differing statistically only from the TAC. As for fatty acids, higher values were found in C 16:0 (TAC) and C 18:0 (TAM), C 20:2 and C 22:5 (control treatment). Microalgae benefited the growth, especially of larger prawns (10 g). However, the factor that benefited the most was not the lipid, but probably the protein present in the microalgae. The provision of microalgae in the form of paste, or powder, can be a good strategy for improving the zootechnical performance of L. vannamei, with less production effort, since microalgae can be produced in the off-season of shrimp production and stored for later use.