Effects of dietary restriction on juveniles of Paralichthys orbignyanus sole
Author: Florencia Gabriela Fóela Farías
Supervisor: Dr Luís André Nassr de Sampaio
Co-supervisor: Dr Ricardo Vieira Rodrigues
Abstract
The aim of the present study was to determine the effects of food restriction on juveniles of Paralichthys orbignyanus sole. For this purpose, fed fish (A) and fish fasted (J) for 8 weeks were compared. Six fish were sampled per treatment in weeks 0, 1, 2, 4 and 8 to compare the use of energy reserves in the liver, plasma and muscle and the effect of food restriction on kidney and intestine morphology. The results showed that fasting produced variations in biometric indices and energy reserves (mainly liver) over time. The condition factor decreased at 8 weeks, while the hepatosomatic and viscerosomatic index decreased after 2 weeks. Plasma cholesterol increased while liver cholesterol decreased,indicating a possible transport for the synthesis of cortisol in response to stress. Plasma glucose, protein and triglyceride levels were maintained over time, the same was observed for osmolality. Plasma glycogen increased at week 8, possibly indicating an accumulation of glucose in the form of glycogen. In the muscle, there was a peak in glucose values at week 4 and an increase in the amount of proteins at week 8. Muscle lipids showed similar variations over time in both treatments, increasing at week 2 in treatment A and 4 in J; antagonically the humidity decreased in both treatments. In the liver there was a significant decrease in glycogen and triglycerides at week 2, and glucose and proteins at week 4. Triglycerides increased at weeks 4 and 8,possibly due to the process of re-esterification of fatty acids, forming lipoproteins. As for histological parameters, there were no differences in the degree of deposition and size of melano-macrophages in the kidney, nor in intestinal morphological parameters. Juveniles of III sole survive for eight weeks on fast using liver energy reserves and without undergoing structural changes in the kidney and intestine.