Study Of Biofloc Formation And Influence On Artemia Growth Under Hypersaline Environment

With the rapid development of high-density intensive aquaculture, discharge pollution and diseases outbreak of the farmed aquatic speices have become increasingly worse. Through adjusting mixing intensity, dissolved oxygen, pH, temperature, organic carbon and organic loading rate, biofloc techniques (BFT) promote microbial conversion of waste and uneaten feed into microbial protein in situ, thus reduce harmful nitrogen (particularly ammonium nitrogen) content and provide supplementry feed for aquatic animals.As a small crustacean, Artemia is not only the major consumer and ecological minitor in medium and high saline ecosystem, but also an excellent live food for larviculture and aquaculture. Application of biofloc technology in high-desnity Artemia culture is taking full advantage of Aretmia being a non-selective filter feeder. Through manipulating measures, heterotrophic bacteria bloom were stimulated, which directly assimilate ammonium nitrogen into microbial protein, and consequently purify water and provide feed protein for Artemia.The experiments were conducted in zero-water exchange Artemia culture system, to study the effects of salinity, mixing intensity, carbon sources and microorganism supplementation on Artemia biomass output, biofloc formation and water quality. Experimental conditions were:temperature 25℃, unit culture volume of 1 L, initial Artemia density of about 1200 ind/L, and concentrated Dunaliella salina as live food. The culture peroid were two weeks, each group contained three replicates. Total Artemia biomass, nutritional composition of Artemia (i.e. crude protein, total fat content and fatty acid profile), total suspended solids (TSS), biofloc volume (BFV), pH, viscosity, concentration of total ammonium nitrogen (TAN), nitrite, nitrateand total nitrogen, etc. in the culture volume were determined. The results were as follows:Experimental groups were set up with culture salinity 50,100 and 150 respectively, glucose was added as carbon source. Salinity 50 and without adding glucose was considered as control. The results showed that with increasing salinity, total Artemia biomass was significantly lower (P<0.05), whilist nitrite and total nitrogen content increased significantly (P<0.05) and BFV increased. Glucose supplymentation and salinity had no significant effect on crude protein and fatty acid content of Artemia (P>0.05). At salinity 50, glucose supplementation significantly improved Artemia total biomass and BFV, and reduced TAN, nitrite, nitrate and total nitrogen concent (P<0.05).Experimental groups were set up with mixing intensity of 400 mL/min,1200 mL/min and 2000 mL/min, respectively, and glucose was added as carbon source. Mixing intensity of the control group was 1200 mL/min and without adding glucose. The results show that, with increase of mixing intensity, Artemia biomass and BFV increased significantly (P<0.05), whilist nitrite and total nitrogen concentration were significantly lower (P<0.05), crude protein content of Artemia was significantly increased (P<0.05). Adding carbon and different mixing intensity had no significant effect on the fatty acid content of Artemia (P>0.05).Different carbon sources (e.g. glucose, sucrose, molasses and corn flour) were added to the culture medium at salinity 50. No carbon was added in the control group. The results showed that adding carbon could significantly improve Artemia total biomass and BFV, lower nitrite, nitrate and total nitrogen content in the culture medium (P<0.05). Among them molasses was the best carbon source.Alkalibacterium sp., Halobacterium sp. and enriched bacterial culture of brine water obtained from the local salt ponds were added into the culture medium at salinity 80. Molasses was chosen as supplemental carbon source. Only microalgae feeding was considered as a control.. The results confirmed that that adding molasses could significantly improv Artemia total biomass and BFV, lower nitrite, nitrate and total nitrogen levels (P<0.05). Adding microbes could promote the growth and survival of Artemia, reduce ammonium nitrogen concentration in water. And Alkalibacterium sp. and Halobacterium sp. were better than enriched bacterial culture.In summary, relatively lower salinity, higer mixing intensity, addtion of carbon sources (particulary molasses) and microbial supplementation effectively reduced ammonium contents in hypersaline zero-exchnage Artemia culutre system, and promoted the growth and survival of Artemia and BFV. This study provides data in aspect of BFT mechanism in hypersaline environment, which will benefit Artemia pond production.