Effect of food restriction and fasting on the activity of the electron transport system (ETS) in juveniles of Pacu (Piaractus mesopotamicus)
The purpose of this work is to test the applicability of a tool normally used in the ecology of aquatic environments in bioenergetics within the aquaculture area, through which the activity of the electron transport system (ETS) was tested on target organs of the species Piaractus mesopotamicus submitted different dietary conditions. The study is based on the hypothesis that ETS activity or the combination of ETS activities from different target organs can be evaluated as a cell biomarker, with the ability to describe or predict zootechnical parameters. The ETS activity assessment method was developed to measure the enzymatic action of ETS by quantifying the oxidation of NADH and NADPH by colorimetry and reduction of 2- (p-iodophenyl) -3- (p227 nitrophenyl) -5-phenyl tetrazolium chloride (INT).The experiment was designed to evaluate the effect of different diets on pacu metabolism, under four treatments: fasting, ad libitum consumption, two other food restrictions with a feed rate of 0.6% and 1% of live weight / day. Each treatment had a minimum of four replicates, a maximum of six (fish) kept in tanks of 100 L of useful volume. The animals were weighed (102 ± 9.5 g) and then kept in acclimatization for 15 days. They were fed daily ad libitum with Supra Anzol de Ouro 24 ® ration, registering the daily consumption from which the food restriction rates were determined. After acclimatization, the initial average weight (115.5 ± 10.4 g) was estimated and the fish were randomly distributed in the experimental units among the treatments. The trial lasted 15 days,with daily monitoring of consumption and water quality. At the end of the experiment, the fish were weighed and then taken blood samples for glucose and hemoglobin analysis and finally euthanized in order to extract the target organs that were used in the analysis of ETS activity in liver, kidney, muscle and gills. A reduction in fasting glycemia and similarity among other treatments were observed. Hemoglobin concentration did not differ between treatments. For ETS activity, it was only possible to observe the influence of treatments on the liver and kidney. In the zootechnical parameters evaluated (weight gain, feed intake, feed conversion and specific growth rate), differences were found in all of them explained by experimental treatments,for which the specific growth rate (TBI) was chosen as a response variable to exemplify the functionality of the ETS indices in the liver and kidney, for the prediction of TBI through mathematical modeling of the data, taking into account that the limited number of data cannot form a highly robust model. However, the model achieved adjusted R2 values of 78%, suggesting that the ETS activity of the liver and kidney showed a potential for the description and prediction of pacu growth.