As the digestive enzymes and gastro-intestinal (GI) bacterial community contribute to the health and nutrition of the organism, this study aims to evaluate the ontogeny of bacterial population and digestive enzymes activities in the GI tract of Artemia urmiana from nauplii to the adult stage. Artemia cysts were hatched under standard conditions and stocked at a density of 20 nauplii ml-1 for 15 days. Samplings for growth, bacterial and enzymatic analysis were collected on days 1, 5, 10 and 15 of the experiment. The results indicated that the GI tract was sterile at the time of hatching. Artemia GI tract was active after hatching by protease (0.282 ± 0.001 U mg-1 protein min-1), lipase (0.182 ± 0.001 U mg-1 protein min-1) and amylase (0.295 ± 0.001 U mg-1 protein min-1) secretion and increased during the experiment. In addition, a significant relation (p < 0.05) was observed between Artemia total length and the activity of digestive enzymes (lipase (r2 = 0.98) amylase (r2 = 0.97) and protease (r2 = 0.98). A significant relation (p < 0.05) was observed between total aerobic bacteria and digestive enzyme secretion (lipase, r2 = 0.83; amylase, r2 = 0.66 and protease, r2 = 0.84) too. Such a relation was observed between total Bacillus spp. count and digestive enzyme activities (lipase r2 = 0.82; amylase r2 = 0.79; and protease; r2 = 0.74). These results suggest that in addition to the chemical composition of food, total length, GI bacteria enzyme secretion and the interaction of these factors contribute in digestive enzymes ontogeny during the growth period.

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