Structure and early development of gill tissue in artificially cultured Eleutheronema tetradactylum

We investigated the structure and early development of gill tissue in artificially cultured Eleutheronema tetradactylum 1−35 d after hatching (DAH) by histological section technique and transmission electron microscopy. The results show that the gill rakers were prick-shaped; the primary lamella on the gill arch were in a comb-like pattern; and the secondary gill lamella were evenly arranged on both sides of the primary lamella. The transmission electron microscopy shows that the secondary lamella consisted of mitochondria-rich cells (two types) pavement cells, pillar cells, blood cells, mucous cells and non-differentiated cells. According to the early development, the gill-primordia appeared on 1 DAH; the primitive gill arch appeared on 3 DAH, containing pavement cells and blood cells; the secondary gill lamella appeared on 5 DAH, and the pillar cells were on the secondary gill lamella; there were scattered mitochondria-rich cells at the base of the secondary lamella which increased and whose structure was basically formed on 18 DAH; the gill structure was basically identical to the adult fish on 35 DAH. The development could be divided into three stages: Stage I was organ-primordium formation (0−3 DAH). During this stage, the gill-primordia formed but undifferentiated, and the respiration was primarily via the finfold, skin and microvascular surface of yolk-sac. Stage II was characterized by differentiation and development of gill filaments (4−17 DAH). During this stage, the gill arches, filaments, secondary gill lamella and gill rakers developed gradually and the basic structure and morphology of the gill were established. During Stage III (18−35 DAH), the gill development was mainly the change in number and shape.