A histological study on the development of the digestive system of Pseudosciaena crocea larvae and juveniles

The ontogenetic development of the digestive tract and accessory organs in large yellow croaker (Pseudoscianea crocea) was described using light microscopy from hatching up to the juvenile stage (40 days post hatch, dph). At 3 dph (4.1 0.1 mm total length, LT), coinciding with the buccopharynx opening, larvae started to feed exogenously, and the digestive tract consisted of a welldeveloped buccopharynx, a partially-differentiated oesophagus, and an intestine divided in three regions (prevalvular and postvalvular intestine, and rectum). Yolk reserves were not completely depleted at the onset of exogenous feeding, and a period of mixed nutrition was observed up to 6 dph (4.3 0.1 mm LT), when yolk was definitively exhausted. Important morphological changes occurred at the end of the larval period, coinciding with metamorphosis. At 17 dph (6.8 0.6 mm LT), pyloric caeca differentiated at the junction of the pyloric stomach and the prevalvular intestine. Gastric glands were firstly observed at 21 dph (9.2 1.2 mm LT), coinciding with the morphological development of the stomach in three different regions (cardiac, fundic and pyloric) according to the histological characteristics of their mucosa. At this age, large longitudinal folds appeared in the median and posterior oesophageal mucosa. These morphological and histological features suggested the achievement of a digestive system characteristic of large yellow croaker juveniles and adults.