OBSERVATION ON THE DEVELOPMENT OF THE HEAD BONES OF THE LARVAE AND JUVENILES OF HEXAGRAMMOS OTAKII

The fat greenling (Hexagrammos otakii) is a commercially important fish in North China. It is not only an ideal species for cage culture, but also optimal for expanding reef bays and developing recreational fishing. Scholars have carried out research on the fat greenling’s embryonic development, early morphology development, as well as spine and appendicular bone development. However, there is a lack of studies on its skull development. This study intends to show the skeletal framework of the fat greenling’s head. It also aims to determine the key processes of bone ossification and timing of development to understand the close relationship between its skull growth and functional development such as feeding and breathing. Samples of the fat greenling larvae were taken once every day and once every 5 days for 0—31 DPH and 35—60 DPH, respectively. The double staining of cartilage and bone procedure was used to analyze the skeletal development of newly hatched fat greenling larvae. The results showed that there were many skeletal elements in the head of the newly hatched fat greenling larvae, including Meckel’s cartilage, palatoquadrate, Hyoidbar and Basibranchial 1. At 4 DPH, the Basibranchial 2 appeared at the posterior end of the Basibranchial1, and the marginal zone extended backwards. The cartilage bridge then emerged, and the skull was divided into anterior and posterior fontanels. At 9 DPH, 3 pairs of Hypobranchial bones and the fifth pair of Ceraobranchial were visible. At 13 DPH, the Meckelian cartilage protruded on the middorsal part, and four pairs of Epibranchial, nasal bone, Lateral Ethmoid and Ehmoidplate appeared successively. At 16—21 DPH, the Basihyal appeared in front of the Basibranchial1. At 23 DPH, the dentary bone began to ossify while the premaxillary and superior maxillary bones started to ossify at 26 DPH, and the ossification process completed at 35 DPH. The ossification of parasphenoid bone, preoperculum, Taenia marginalis, metapterygoid bone, nasal bone and symplectic bone was completed at 50 DPH. At 60 DPH, except the Hyoidbar bone, the skeletal framework of the fat greenling’s head was completely ossified. The results showed that it takes a long time for the development of the fat greenling’s skeletal framework, and the early growth of its skull is closely related to the enhancement of the feeding and respiratory capacity of the larvae. The results of this study not only explain the growth and development process of the fat greenling’s skull, but also provide scientific basis for early functional development research and identification of skull deformities.