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During the early ontogeny, the transition from endogenous (yolk protein) to exogenous feeding (artificial diets) represents a critical period linked to the undifferentiated digestive system, with low digestibility of food protein. The objectives of this work were to characterize the morphology of the early Nile tilapia (Oreochromis niloticus) developmental stages and determine the activity of alkaline and acid peptidase enzymes during the ontogenesis from hatching to 20 days post-hatching (DPH). Also, the in vitro effect that exogenous enzymes from Argentine red shrimp (Pleoticus muelleri) waste have on the alkaline peptidases of larvae from 6 to 20 DPH (which correspond to the age at which fish eat exogenous food) was studied. Both acid and alkaline peptidase activities varied throughout early ontogeny development (from 0.1 to 1, and from 0.1 to 7.1 UE mg protein−1, respectively). The patterns of both enzyme activity variation would be related with changes in endogenous, mixed and exogenous feeding. Our studies show that the additions of the enzyme extract of shrimp have a synergistic effect (from 3 to 6 times) on endogenous in vitro activity. Moreover, the zymogram analysis demonstrates that the bands corresponding to the activity of each species (tilapia and red shrimp) remain active when they are mixed. The increase in peptidase digestive capacity by addition of exogenous enzymes would maximize the assimilation of nutrients from artificial food during early development. [ABSTRACT FROM AUTHOR]

In spite of their ecological importance in tidal pools, studies on digestive flexibility in non-symbiotic anemones (i.e., without symbiosis throughout their life) upon changes in key environmental factors are lacking. This study constitutes the first work to investigate the response of digestive enzymes in relation to high environmental salinity and temperature in a non-symbiotic sea anemone. We determined the occurrence and biochemical characteristics of maltase activity and compared maltase and proteolytic activities in mesenterial filaments in Bunodosoma zamponii from the intertidal area of Punta Cantera, Mar del Plata, Argentina (38°05′S, 57°32′W) acclimated to 35 and 40 psu and after an acute enhancement (15 min) of temperature from 20° to 30°C. Maltase activity was higher in 40 psu and upon the increase in temperature (about 80 and 99%, respectively). Proteolytic activity was not affected in any case. The results suggest the occurrence of specific digestive adjustments in relation to high salinity and temperature. The fact that differential modulation of maltase activity could be associated with a higher digestive capacity for glycogenic substrates is discussed. [ABSTRACT FROM AUTHOR]