CHARACTERIZATION OF LARVAL DIGESTIVE SYSTEM ONTOGENY IN Corydoras aeneus

Understanding species- specific larval digestive system ontogeny is critical for formulating effective feeds and feeding protocols in aquaculture. Some species exhibit extended agastric larval stages, during which time hydrolysis of macronutrients is dependent primarily upon digestive enzymes of pancreatic and intestinal origin. Other species emerge from the egg with a fully formed and differentiated gastrointestinal system, indicating a much higher capacity for digestion and assimilation of diverse prey. The current study used histological and histochemical preparations, as well as analysis of digestive enzyme activities, to characterize the embryonic and larval digestive system ontogeny in the Bronze Cory  Corydoras aeneus .

Samples of 15 individuals were taken  at 3 days post fertilization (embryos), 1 days post hatch (dph ), 2 dph , 3 dph , 5 dph and 8 dph . Five fish were assayed to determine trypsin and bile-salt dependent lipase activities, five to determine pepsin activity, while the remaining five were fixed in Trump's solution for histological processing. Histological processing consisted of fixation in epoxy, followed by staining with hematoxylin and eosin, as well as periodic acid Schiff stains to visualize the production of neutral mucopolysaccharides, which are present during acid production by gastric glands. A stomach anlage was apparent in the 3 dpf embryos, although gastric glands were not visualized. A functional stomach was apparent at 1 dph, which preceded the complete absorption of yolk and the onset of exogenous feeding.  Although gastric glands were present at 1 dph , pepsin activity was not detected until 2 dph (Figure 1) , when exogenous feeding began. These results corroborate preliminary research that indicated a high digestive competency of  C. aeneus from first feeding , in which commercially available microparticulate diets outperformed live Artemia nauplii.