Ontogeny of the digestive tract with special reference to the acid and alkaline protease capacity in Sobaity (Sparidentex hasta)

This study aims to assay the main protease (pepsin and trypsin) activity and pepsinogen relative gene expression, as well as histological development of digestive tract in Sobaity from hatching up to 40 days post- hatch (DPH). The results showed that exocrine pancreas, including zymogen granules, differentiated during yolk sac absorption and further developed at 14 DPH. The early appearance of trypsin before mouth opening is attributed to a genetically programmed process. The trypsin activity showed fluctuated pattern (with two peaks at 16 and 30 DPH), coincident with food intake, and related to diet shifting during larval feeding. The most obvious differentiation in the digestive tract was the formation of an incipient stomach surrounded by striated muscle fibers and the development of the gastric glands at 12 DPH. The stomach fully developed at 25 DPH with the transition from striated to smooth muscle cells. The pepsinogen relative gene expression was not detectable before 12 DPH and meaningfully detected at 14 DPH. The pepsinogen expression augmented exponentially coinciding with shifting diet from live to microdiet. Pepsin activity trend was considerably parallel to pepsinogen and started two days after pepsinogen, subsequently increased sharply during the weaning period (25-30 DPH) up to the end of the study. The study concluded that the appearance of the incipient stomach at 12 DPH, early pepsinogen expression, and ontogenetic development of pepsin and trypsin, make it possible to feed Sobaity larvae by inert diet before 25 DPH to reduce the live food consumption and improve the weaning efficiency.