Morphometric and fin dimorphism between sex in the marine medaka, Oryzias dancena

Abstract

Sexual dimorphism is the most conspicuous difference between the sexes. This study examines possible sexual dimorphism and the relative growth patterns of morphometric characteristics in the marine medaka, Oryzias dancena for their potential to help differentiate between males and females of this species. And I am about to consider more about difference of male and female of marine medaka in morphology seen from anal fin and fin ray as well as dorsal fin. The von Bertalanffy growth parameters estimated by a non-linear regression method were L∞=30.2 mm, K=3.22/year, and τ0=-0.05. All 18 characteristics measured showed a difference between males and females from 70 days after hatching. Five direct distance characteristics included the following: the anterior insertion of the first dorsal fin and the anterior insertion of the first anal fin, the direct distance between the posterior insertion of the last dorsal fin and the anterior insertion of the first anal fin, the direct distance between the anterior insertion of the first dorsal fin and the posterior insertion of the last anal fin, the length of the fin rays of the dorsal fin, and the length of the fin rays of the anal fin. Each of these characteristics were significantly different between sexes (ANCOVA, P<0.05), and the ratio of standard length between sexes showed that males were larger than females for all five characteristics.

Fin length measurements were taken for 21 distances of anal fin and 7 distances of dorsal fin between landmarks. There were all difference for all dorsal fin rays between the males and the females and there is significant difference in 70 days after their hatched when the sexual dimorphism is presented. The significant difference (P<0.05) in fin ray for male and female was more greatly seen as they grow. Male marine medakas showed more rapid growth than females, with longer length, dorsal fins and anal fins. Differences in these characteristics will be useful during experiments when it is necessary to differentiate between sexes of marine medaka.