Morphometric Characteristics and Fin Dimorphism between Male and Female on 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. 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. 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 morphometric measurements. Fin length measurements were taken for 21 distances of anal fin and 7 distances of dorsal fin between landmarks. There were all differences for all dorsal fin rays between the males and the females and there is significant difference in 70 days after their hatch 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 medaka 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.

Morphometric Characteristics of Diploid and Triploid Marine Medaka, Oryzias dancena

“…As mentioned by Kim et al (2009b) , it is easy to classify the sexual dimorphism of the marine medaka through the forms of the dorsal and anal fins. Im et al (2016) also reported that the sexual dimorphism of the diploid marine medaka is evident in the difference in growth 70 days after hatching, with apparent differences in DADAA, DPDAA, DADPA, LFRsD, and LFRsA, with the male characteristics larger than those of the female. The characteristics of the dorsal and anal fins of the marine medaka are significantly different between the males and females.…”

“…There are a number of techniques for separating diploid and induced triploid fishes ( Thorgaard et al, 1982 ; Wolters et al, 1982 ; Park et al, 2016 ). The three most widely accepted methods now used are flow cytometric measurements of erythrocyte DNA ( Thorgaard et al, 1982 ; Park et al, 2016 ), Coulter counter estimation of erythrocyte nuclear size ( Thorgaard et al, 1982 ; Park et al, 2016 ), and measurement of erythrocyte nuclear volume by light microscopy ( Wolters et al, 1982 ; Park et al, 2016 ). Unfortunately, the first two methods are very expensive, and light microscopy is time-consuming and insufficiently accurate for widespread use.…”

“…The fertilized eggs of the triploid experimental group ( n =500) were left to fertilize for 5 min, and were subjected to cold-shock treatment (4℃) for 60 min to prevent the expulsion of the second polar body ( Park et al, 2016 ). The treated eggs were reared in a 100 L glass aquarium.…”

“…Standard length measurements were made from the pictures to the nearest 0.01 cm, using digital Vernier calipers (CD-20CP; Mitytoyo, Japan). Using the methods of Im et al (2016) , body outline measurements were made for 19 distances between landmarks for both truss and classical dimensions ( Fig. 1 , Table 1 ).…”

The Sterilization Effect of Methylene Blue, Formalin, and Iodine on Egg and Adult Stage of Marine Medaka, Oryzias dancena

“…We adopted the experimental marine medaka, Oryzias dancena because the marine medaka is gaining attention as an experimental animal in the aquaculture. This fish is a truly euryhaline teleost with a great capacity for hypo- and hyper-osmoregulation (Roberts, 1998; Im et al, 2016). It also has a short interval between generations with spawning possibilities just 60 days after hatching (Song et al, 2009; Park et al, 2011, 2016, 2017, 2018).…”