Ontogenetic changes in behaviour transmission among individuals in the schooling of Pacific bluefin tunaThunnus orientalis

Abstract

-To reveal the kinematical aspects of schooling development in the Pacific bluefin tuna Thunnus orientalis, changes in its schooling behaviour traits, local behaviour transmission among school members and morphological traits were investigated as fish developed from the larval to the juvenile stage. Schooling was first observed at around 24 days post-hatching (27 mm body length) in T. orientalis. Behaviour transmission among individuals took much longer among 24 d post-hatching individuals than among older fish. The compactness and polarity of the school progressively improved as the time required for behaviour transmission decreased. One cause of the reduction in the time required for behaviour transmission was the development of manoeuvrability, which resulted from further morphological development of the caudal fin and other organs related to swimming.

Appropriate size for transportation to sea cages for juvenile Pacific bluefin tuna Thunnus orientalis (Temminck and Schlegel)

“…The results were compared with control‐1, which had been previously used (Honryo et al., 2018). On the other hand, many PBF juveniles die due to collisions, which frequently occur when they are above 60 mm in total length (Miyashita, 2002) because their swimming ability develops rapidly after the juvenile stage (Fukuda et al., 2011). Therefore, we tested another, opposing hypothesis that survival could be improved if transportation was carried out before the swimming ability of PBF developed.…”