Early Development of the Spinal Vertebrae and Appendicular Skeleton in Miichthys miiuy Larvae

We investigate the early developmental characteristics of the skeletal system in Miichthys miiuy larvae using a double staining method on the whole larval skeletons (aged 1-30 days). We systematically observed and described the morphological development of both the spinal vertebrae and appendicular skeleton. The results showed that there were 25 spinal vertebrae in M. miiuy, which consist of 12 abdominal vertebrae and 13 coccyges; The development of spinal vertebrae began at 12 days after hatching (dah), with the emergence of ossified neural and haemal arches, where ossification appeared at 17 dah; and the appendicular skeletons were developed from the pectoral fins to ventral fins. The coracoid-scapula cartilage was clearly observable at three dah, and fin rays were clearly differentiated at 21 dah. The cartilage of appendicular of the ventral fins was formed until 19 dah, and the ventral fins were completely ossified at 21 dah. Subsequently, the caudal, dorsal, and anal fins appeared at 10, 13, and 14 dah, respectively. Additionally, the appendicular skeleton associated with the movement of M.miiuy was completely developed by 28 dah. Finally we observed that there are four types of spinal vertebrae abnormalities during the early development of M.miiuy, which included spinal bulging, splitting of vertebrae, and supernumerary and bifurcated haemal and neural spines. Skeletal length and age (in days) were highly correlated (r(2) = 0.942). There was a strong relationship between total length and skeletal length (r(2) = 0.979) and between body length and skeletal length (r(2) = 0.9779).