Seawater tolerance of newborn guppies was measured by way of survival rates 24h after transfer to seawater. The newborn guppies showed high seawater tolerance and some of themsurvived in 35 ppt seawater. Seawater tolerance significantly decreased within 5 days after birth and then became stable at a level comparable to adults. After a challenge test with 35 ppt seawater at birth, the surviving individuals remained alive more days and grew in 35 ppt seawater. They yielded offspring, and most of their progeny survived in 35 ppt seawater. Therefore, the guppies could propagate in seawater and a seawater-tolerant strain was established.
The Japanese Society of Fisheries Science