THE PSEUDOBRANCH DEVELOPMENT IN EASTERN MOSQUITO FISH GAMBUSIA HOLBROOKI, GIRARD 1859 (CYPRINODONTIFORMES, POECILIIDAE) FROM JADIRIYAH LAKE, BAGHDAD, IRAQ

The aim of the current investigation is to study the embryogenesis of the pseudobranchia (PB) in the Eastern mosquito fish Gambusia holbrooki, Girard, 1859 (Cyprinodontiformes, Poeciliidae). Histological sections from 2-4 mm long embryos revealed the presumable PB as a cell mass surrounded by a row of squamous cells in the operculum, as well as the formation of cartilage and blood vessels, and the beginning of the formation of its lamellae. In 5-7.75 mm long embryos, a prominent rise appeared in the mass of cells and PB lamellae, along with an increase in melanin deposition around the blood vessels. Moreover, a row of squamous cells encircled the rise from the front and back. At this stage, the parallel arrangement of the cartilage-attached lamellae correlated with increased melanin concentration around the blood vessels. In newborns, the differentiated cells increased similar to that appearing in the adult’s stages.