ANALYZING SURVIVAL FACTORS OF NAUPLII IN FRESHWATER ON ARTEMIA IN TIBET AUTONOMOUS REGION, CHINA

Artemia is an important living bait in Tibet Autonomous Region, China, which has been widely used in aquaculture and breeding practice. The survival time of nauplii in freshwater affects the utilization rate of feeding. This study explored the effects of different sodium salts on hatching rates and survival time of nauplii in freshwater. The nauplii survival time of Artemia in Tibet in freshwater under different NaCl contents, incubation pH and freshwater temperatures were analyzed, and the 50% and 100% of nauplii mortalities in freshwater were recorded to provide reference for breeding practice. The results indicated that different sodium salts significantly affected the hatching rate of Artemia in Tibet with the highest hatching rate in Na₂SO₄ group was significantly higher than that in NaCl group (P<0.05), the lowest hatching rate in Na₂CO₃ was significantly lower than that in NaCl group (P<0.01), and no significant difference among other groups (P>0.05). The survival time of nauplii hatched in the NaCl group was the longest with a 50% survival time of 13 hours, while the survival time of nauplii hatched in the Na₂SO₄ group was shorter than that in NaCl group (P<0.05). The lowest survival time of nauplii was the Na₂CO₃ group, and both Na₂CO₃ and NaNO₃ groups had lower hatching rate than that in NaCl. The mortality of nauplii hatched in Na₂CO₃ was the fastest among all groups. These results indicated no correlation between hatching rate and survival rate. As the hatching salinity increases, the survival time of nauplii in freshwater gradually prolonged and reached the longest at the salinity of 35‰, but when the hatching salinity reached 40‰, the survival time began to decrease. As pH increases from 6.5 to 8.0, the survival time of nauplii increased and reached the longest at pH=8.0, and then the survival time gradually decreased when incubation pH continued to increase. 50% survival time of naupliiwas only 3.54h at pH 10.0 with the highest mortality. The 50% survival time of nauplii incubated in pH8.0 was prolonged compared with other groups (P<0.05). The 50% death time of nauplii in freshwater at 5℃ was 18.54h, which was significantly longer than that in the 15℃ group. When the water temperature was ≥20℃, the 50% survival time in all groups decreased significantly than that in the 15℃ group (P<0.05). These results indicated that sodium salt, salinity, incubation pH, and freshwater temperature have significant effects on the nauplii survival time in freshwater of Artemia in Tibet Autonornous Region.