THE DIGESTIVE FUNCTION OF Pseudoplatystoma punctifer EARLY JUVENILES IS DIFFERENTIALLY MODULATED BY THE DIETARY PROTEIN AND LIPID LEVELS AND THEIR RATIOS

T he effect of different dietary protein and lipid levels in the expression of several digestive genes  during the early development of Pseudoplatystoma punctifer ,  an Amazonian catfish with high aquaculture potential, was evaluated.  Larvae  were fed Artemia nauplii from 4 to 12 days post fertilization (dpf ) and weaned  from 13 dpf  onto  compound di ets  containing different protein:lipid levels (30:15, 30:10, 45:15 or 45:10) .  The expression of trypsinogen-try , chymotrypsin-chy , amylase-amy , lipoprotein lipase-lpl , phospholipase-phl and pepsinogen-pep  was analyzed at the end of the Artemia  (12 dpf ) and compound diet (26 dpf ) feeding periods in order to better understand the digestive function and nutritional needs of this species.

F ig. 1 Relative phospholipase  and  pepsinogen gene expression at 12 and 26 dpf in Pseudoplatystoma punctifer early juveniles fed four different dietary treatments. Results are expressed as mean ± standard deviation (n=3).  Letters denote significant differences between  dietary groups and asterisks indicate significant differences among age  within a  dietary group (One- way  ANOVA, P < 0.05).

Except for pep expression, that was highest in 45:10 group, no differences were found in the expression of the analyzed digestive genes during the Artemia feeding period (12 dpf). However,  digestive  genes were differentially modulated  by the different compound diets  (26 dpf ). Tryp , amy , phl and pep expressions were highest in 45:15 group, whereas lpl expression was highest in 45:10 group and lowest in  30:15 and 30:10  groups.  Groups  30:15, 30:10 and 40:10 showed  similar levels of amy  and phl expression . Try expression was lowest in 30:10 group followed by  30:15  and 45:10 groups, where as  the lowest pep expression was observed in 30:15 and 30:10 groups followed by 45:10 group. No significant differences were found in chy expression among the four dietary treatments. Try and lpl expressions increased during development in all groups with the exception of groups 30:10 and 30:15, respectively. Phl expression increased during development in 45:15 and 45:10 groups while it remained stable in the others . Chy expression decreased during development in 45:10 group  and amy expression increased during development in 45:15 group  whereas their expression remained invariable in the rest of the groups . Pep expression increased during development in all dietary groups. In conclusion,  the dietary  protein and lipid content and their ratios modulated the digestive function in  P. punctier early juveniles. Thus, the better growth and survival and  the lower incidence of cannibalism observed in 45:15 group might be explained by the better digestive performance showed by these individuals.