Influence of swimbladder inflation failure on mortality, growth and lordotic deformity in Pacific bluefin tuna, Thunnus orientalis, (Temminck & Schlegel) postflexion larvae and juveniles

摘要

This study examined the influence of swimbladder inflation (SBI) failure on mortality (Experiment 1), lordotic deformity (Experiment 2) and growth (Experiment 1, 2) in Pacific bluefin tuna, Thunnus orientalis, postflexion larvae and juveniles by producing larvae lacking inflated swimbladders. Experiment 1 was conducted for postflexion larvae to juveniles (from 18 to 30days-post-hatch; dph). Mortality was not significantly different between the fish with (WIS) and without (WOIS) inflated swimbladders. Standard length (SL) and body weight (BW) were significantly smaller in WOIS than WIS. Moreover, the SBI was found in WOIS after postflexion stage. In Experiment 2, two examination trials were conducted on SBI, vertebral deformity and growth for juvenile stage. Lordotic deformities were found neither in the WOIS nor in the WIS. Although SL and BW were significantly smaller in WOIS than WIS at 22dph, after 37dph no significant differences were found between them. The results of Experiment 1 and 2 indicate that SBI failure causes growth retardation until juveniles of 30dph; however, it does not cause growth retardation in juveniles after 37dph and mortality of postflexion larvae and juveniles. Moreover, SBI failure did not cause lordotic deformity in PBT differently from many other fish.