Decline in Salinity Tolerance during Larval Stage of Chum Salmon Oncorhynchus keta

To elucidate salinity tolerance of chum salmon Oncorhynchus keta at an early life stage, the present study examines changes in salinity tolerance during their larval stage. All of the larvae 5 days after hatching survived in 45 ppt seawater but died in 55 ppt seawater. However, all of the larvae 20 or 30 days after hatching and the fry 60 days after hatching died in 40 ppt seawater. The LD sub(50) of salinity was 49.2 ppt 5 days after hatching but gradually and significantly decreased to 35.8 ppt within 30 days after hatching. Fry 60 days after hatching showed the same LD sub(50) as that of the larvae 30 days after hatching. These results indicated that salinity tolerance of chum salmon larvae significantly decreased within 30 days after hatching, at the time the yolk had almost been completely absorbed.