The effect of different levels of water alkalinity on growth and reproductive parameters of Artemia franciscana in the biofloc based culturing system

The effect of different levels of water alkalinity on growth and reproductive indices of Artemia franciscana was investigated in biofloc culturing system. First, different levels of alkalinity (75, 150, 225, and 300 mg/l calcium carbonate) were provided in biofloc-based conditions; and then the best alkalinity level (in terms of nutrients contents and biofloc production volume) was investigated on the growth and reproductive indices of Artemia in two treatments containing the control group (Artemia grown in green water- mainly containing Dunaliella salina) and biofloc group. Biofloc production volume was significantly higher in 150 mg/l compared to other treatments (p<0.05). Also, the protein content of biofloc mass was higher in 150 mg/l, and was significantly higher than 75 mg/l (p<0.05). Total ammonia, nitrite, nitrate, BOD, and TSS in biofloc treatment showed higher values than algal treatment. By increasing the water alkalinity, total hardness, total nitrogen, nitrite, and nitrate increased significantly in biofloc group (p<0.05). The ratio of omega-3 to omega-6 fatty acids, and also the eicosapentaenoic to dicosahexanoic acid ratio in algal treatment were significantly higher than that of biofloc group (p<0.05). Accordingly, the alkalinity of 150 mg/l was proposed as the best alkali level for biofloc production. Considering the quantitative and qualitative characteristics, 150 mg/l alkalinity was recommended as the best level of alkalinity for biofloc production. At the end of the culture period, the comparison of growth rate and reproductive indices of Artemia in two groups showed that, despite no significant differences between groups, Artemia fed on algae indicated relatively better reproductive indices with respect to spawning frequency and total number of births (total length: 52.9, spawning frequency: 4, total number of births: 182.82 in algal treatment versus total length of 42.9, spawning frequency: 3.6 and total number of births: 130.66 in biofloc treatment). The survival rate, the time required for sexual maturation, and the ratio of cyst per nauplii production were higher in the biofolc group (survival rate: 80.2, the duration of sexual maturation (day): 18.8 and the ratio of cyst to nauplii production: 66.6% in biofloc treatment versus survival: 78.4, the duration of sexual maturation (day): 18.2 and the ratio of cyst to nauplii production: 56.4 in algal treatment). Based on the results, feeding Artemia with biofloc feed instead of algae is possible for the growth and mass production of Artemia on small-scale culture systems.