Daily periodicity and movement behavior rule of juvenile yellowfin tuna（Thunnus albacares）during ingestion period

【Objective】To study the movement behavior of juvenile yellowfin tuna（Thunnus albacares）on the basis of land-based recirculating aquaculture，and to establish an institutionalized tuna aquaculture technology system，so as to lay a foundation for the follow-up development of deep sea aquaculture and land-based recirculating aquaculture in China. 【Method】Acclimatized juvenile yellowfin tuna（acclimated for 30 days）were tested in an indoor intensive recirculating aquaculture system，and their ratio of full-length to diameter，swimming speed and depth during ingestion and non-ingestion period were determined by underwater camera technology to analyze their ingestion and daily periodicity movement behavior.【Result】The swimming speed of juvenile yellowfin tuna was slower in morning and at dusk，but faster at 8:00- 10:00 and 14:00-16:00. When it first found food，the swimming speed was faster，reaching 1.84-3.90 m/s，and the sprint distance was 4.80-5.51 m. Juvenile yellowfin tuna rushed to food at a speed of 0.98-1.54 m/s during ingestion and sprint distance of 0.61-1.09 m. The initial ingestion depth of juvenile yellowfin tuna ranged from 0.83 m to 1.43 m，and the linear equation between ingestion depth（y）and feeding time（x）was y=0.0002x²–0.021x+1.168（R²=0.360）. With the extension of feeding time，the difference of ingestion depth among juvenile yellowfin tuna increased gradually. When the total length of yellowfin tuna was 38.63-51.25 cm，its 45° diameter was 1.87-3.38 cm，and its 90° diameter was 3.45-6.00 cm. The body length was positively correlated with the diameter. In the process of land-based recirculating aquaculture，the water depth of yellowfin tuna was the deepest at 6:00 in the morning and fluctuated slightly from 8:00 to 18:00. The ingestion depth changed from deep to shallow and then slowly to deep with the extension of feeding time.【Conclusion】Juvenile yellowfin tuna still have periodic changes in swimming speed and swimming depth under land-based culture condition. As the feeling of hunger declines，juvenile yellowfin tuna are gradually less and less motivated to ingest. To ensure their safety，yellowfin tuna will not ingest actively when the distance between food and the bottom of the pool is less than 0.70 m. This conclusion can provide basic data for the study on the rhythmic habitat depth and swimming behavior of yellowfin tuna，and guide the optimization of yellowfin tuna land-based breeding technology.