Ontogenetic Development of Gill and Na+/K+ ATPase in the Air-Breathing Loach

This study aimed to explore the gill developmental mechanism of the high mortality rate of Paramisgurnus dabryanus larvae in the early life-history process. Based on histological observations with a optical microscope, we studied the ontogeny of the gill of P. dabryanus. The result indicated that external gills first appeared 12 h after hatching. The number of external branchial filaments greatly increased at 2 d after hatching (DAH). The internal branchial filament primordial was formed in the oropharyngeal cavity at 5 DAH. At 9 DAH, none of external branchial filaments were observed outside, but the fish operculum was completed covered. From 15 DAH forward, the filaments and lamellae of gills increased in number and length prominently, and the gills of the larvae were similar to those of juvenile fish. The specific activities of Na+/K+-ATPase steadily increased from 0 to 12 DAH and peaked at 15 DAH. After 15 DAH, the specific activities of Na+/K+-ATPase slightly decreased and then tended to remain steadily stable until the end of the experiment. There were abundant gill lamellae on the gill filaments at 40 DAH. The sensitive period of the development of larval and juvenile P. dabryanus was from 6 to 15 DAH. Our results provide information that may be useful for improving our understanding of the life history and ecology of loaches.