Abstract
Japanese medaka (Oryzias latipes) is known to deposit fertilized eggs on aquatic substrates in shallow waters. In order to examine the influence of water depth on embryonic development of fertilized eggs of an orange-red variety and wild medaka, we observed fertilized eggs for 18 days and compared the hatching rate and the hatching time at different water depths of 5, 30, and 65 cm. The hatching rate was lower at 65 cm depth than at 5 cm depth and the hatching time was longer at 65 cm depth than at 5 cm depth with both the orangered variety and the wild medaka. These results indicate that deep water is not suitable for the embryonic development of medaka and suggest that preservation of natural conditions in shallow waters of rivers and ponds is important for conservation of wild Japanese medaka.
