| Yellowtail kingfish (Seriola aureovittata) is a pelagic migratory fish species with a global distribution. In recent years, the worldwide interest in the aquaculture of this species has increased because of its high flesh quality and fast growth. As a large and fast-swimming pelagic fish, the yellowtail kingfish has a good adaptability to land-based industrial recirculating and offshore net cage modes. With the development of aquacultural technology, more and more attention has been paid to the animal behavior research, which will promote the welfare level in aquaculture. Light, sound, temperature, density, and flow velocity are important factors affecting the welfare level of farmed fish. The development, morphological structure, and regulatory mechanism of sensory organs, including visual, gustatory, olfactory, and auditory organs, are becoming more and more important in the study of animal behavior.
Orthodenticle homeobox 2 (OTX2) and eye absent 1 (EYA1) play important roles in regulating the ontogeny, differentiation, and development of visual, gustatory, olfactory, and auditory organs. In order to study the expression characteristics of otx2 and eya1 in yellowtail kingfish during early development. otx2 and eya1 were identified from brain tissue with specific kits. The lengths of otx2 and eya1 open reading frame domain were 876 bp and 1962 bp, and encoded 291 amino acids and 653 amino acids, respectively. In which, OTX2 consists of a homologous domain between 42nd to 93rd amino acids and a TF-Otx domain containing 82 amino acids; the C-terminal of EYA1 is an EYA domain encoding 246 amino acids. These two genes had a wide range of tissue expression characteristics, which including eye, brain, pituitary, head kidney, heart, liver, spleen, kidney, mid-gut, and ovary. The highest expression level of otx2 was obtained in eye, followed by brain, and the values in these two tissues were significantly higher than those in other tissues (P<0.05). The highest expression level of eya1 was obtained in pituitary, followed by ovary, and the values in these two tissues were significantly higher than those in other tissues (P<0.05). During the embryonic development, expressions of otx2 and eya1 could be detected in each stage, and levels were upregulated in the late stage. In which, otx2 reached its peak value at hatching stage, and eya1 reached its peak value at embryo encircling 4/5 of yolk sac stage. In the larval and juvenile stage, expressions of otx2 and eya1 can be detected in each stage, and the high expression levels are traced in the early stage. In which, expression level of otx2 was firstly upregulated and then downregulated; expression level at 3-25 dph was significantly higher than those at 1 dph and 30-60 dph, and the highest level was significantly reached at 20 dph (P<0.05). Expression of eya1 showed a down trend, the highest level was significantly reached at 1 dph (P<0.05), and expression level at 30-60 dph was significantly higher than those at 7-25 dph (P<0.05). This study provides a molecular basis for understanding the physiological functions of otx2 and eya1 during the development of the sensory organs and the regulatory mechanisms in yellowtail kingfish. |
