Eyespot rasbora ventral area of the body between the operculum and the pelvic fins (corresponding roughly to the sac enclosing the alimentary canal). Under conditions of reflectied light, the fish sometimes displays a fine lateral band from the opeculum to the end of the caudal peduncle (Walker, 1971, p. 98) this being an olive-gold hue. The fins, with the exception of the dorsal fin, are hyaline, the relation of the pectoral and pelvic fins being typical of the ostariophysans (fishes possessing an auxiliary mechanism for detecting sound consisting of a set of internal bones called the Weberian Ossicles). In such fishes, the
Operculum (fish) over time. The fossil record of the threespine stickleback provide the ancestral shapes of the operculum bone. Overall, the operculum bone became more triangular in shape and thicker in size over time. Genes that are essential in the development of the opercular series is the Eda and Pitx1 genes.These genes are known to be a part of the development and loss of armor plates in gnathostomes. The Endothelin1 pathway is thought to be associated with the development of the operculum bone since it regulates dorsal-ventral patterning of the hyomandibular region. Mutations in Edn1-pathway in zebrafish are known to lead to