• Korean Journal of Ichthyology
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• v.27 no.3
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• pp.228-232
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• 2015

The structure of the ventricle in the heart of Hypomesus nipponensis was investigated by light and scanning electron microscope. The heart consisted of four consecutive chambers, the sinus venosus, atrium, ventricle and bulbus arteriosus. The wall of the ventricle was divided into endocardium, myocardium, subepicardium and epicardium. The valves were observed in the artrioventricular and bulboventricular junctions. The ventricular myocardium was an entirely spongy without coronary vessels. The trabecular network was formed with lumina included a central lumen and the trabecula was cylindrical shape. Collagen distribution was apparent in the subepicardium, artrioventricular valve and bulboventricular valve. But in the trabeculae, collagen distribution was observed partly in the base of the ventricle. Especially, the endocardial bridges were observed between trabeculae. These results might be considered that the structure of the ventricle in the heart of pond smelt is adapted to sedentary habit associated with its habitat and lifestyle.

• Development and Reproduction
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• v.17 no.1
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• pp.45-53
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• 2013

The action of melatonin within the body of animals is known to be mediated by melatonin receptors. Three different types of melatonin receptors have been identified so far in fish. However, which of these are specifically involved in puberty onset is not known in fish. We cloned and analyzed the sequence of melatonin receptor 1a (mel 1a) gene in Nile tilapia Oreochromis niloticus. In addition, we examined the tissue distribution of gene expressions for three types of receptors, mel 1a, 1b and lc and investigated which of them is involved in the onset of puberty by comparing their expression with that of gonadotropin-releasing hormone receptor I (GnRHr I) gene using quantitative real-time PCR from 1 week post hatch (wph) to 24 wph. The mel 1a gene of Nile tilapia consisted of two exons and one bulky intron between them. Mel 1a gene was found to be highly conserved gene showing high homology with the corresponding genes from different teleost. All three types of melatonin receptor genes were expressed in the brain, eyes and ovary in common. Expression of mel 1a gene was the most abundant and ubiquitous among 3 receptors in the brain, liver, gill, ovary, muscle, eye, heart, intestine, spleen and kidney. Mel 1b and mel 1c genes were, however, expressed in fewer tissues at low level. During the development post hatch, expressions of both mel 1a and GnRHr I genes significantly increased at 13 wph which was close to the putative timing of puberty onset in this species. These results suggest that among three types of receptors mel 1a is most likely associated with the action of melatonin in the onset of puberty in Nile tilapia.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.20 no.1
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• pp.16-23
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• 1987

The cyprinid loach, Misgurnus mizolepis $G\ddot{u}nther$, a freshwater teleost, is a member of the family Cobitidae and is known to distribute in Korea and China. This fish is considered to be an excellent food fish in Korea. This report is a description of the gross morphology of the embryos and larvae up to the development of juvenile period of life. The eggs were obtained by injecting gonadotropin and fertilized by wet method in the laboratory on July 10 in 1986. The inseminated eggs were rinsed with tap water and incubated at $25^{\circ}C$. Live, freshly laid eggs were separative, demersal, adhesive, light yellow and average 1.1mm in diameter. The hatching took place in about yellow and average 1.1mm in diameter. The hatching took place in about 24 hours after fertilization. The newly hatched larvae were average 2.7 mm in total length possessing yolk sac and 35-36 myotomes. Ten hours after hatching, the prelarvae attained 3.5 mm in total length. The first heart pulse and melanophores at the side of the body were observed at this stage. Yolk sac was completely reserved at four days after hatching. The larvae that was cultured 24 days after hatching, 15.4-16.4 mm in total length, entered the juvenile period of life. All the un rays were already peresent; D. III 6, A. III, 5, P.10, V. 4-5, C.14.