Açaí (Euterpe oleracea) in diets for Tambaqui juveniles (Colossoma macropomum): growth performance, redox status, energy metabolism and neuroprotective effect
This study aimed to evaluate the dietary inclusion of lyophilized açai Euterpe oleracea (LEO) as a growth promoter for tambaqui juveniles (Colossoma macropomum), through the measurement of skin pigmentation, antioxidant status, energy metabolism, besides the implications of its intake on resistance to cope with transport stress and neuroprotective activity. The fish (0.92 ± 0.01 g) were fed for 30 days with six isoenergetic and isoprotein diets containing 0.00; 0.63; 1.25; 2.50; 5.00; and 10.0% LEO (w/w). A growth 7-fold higher than the initial weight was achieved at the end of the feeding trial. The inclusion of 5.00% and 10.0% LEO in the diet was significant in terms of weight gain and final body weight. The intake of 1.25% LEO by tambaqui also improved the parameters of feed efficiency, increasing the specific growth rate (SGR). The antioxidant capacity (DPPH), as well as the flavonoids and polyphenols content, were not increased in the muscle. However, dietary açai at 5.00%, intensify of the cyan color in the skin. The lowest açai inclusion level (0.63 %) resulted in higher intestinal antioxidant competence (39.57%), which was not observed in the liver and muscle. In the intestine, the estimated inclusion of 5.47% LEO minimized TBARS levels, while in the liver and muscle there were no significant differences. The inclusion of LEO in the diets showed to be economically feasible up to 1.25% LEO (Chapter 1). Reduction in the muscle triglyceride content (40%) in the muscle was obtained by the intake of 0.63% LEO. Despite this, there were no significant changes in cholesterol, glucose, glycogen and total protein levels in this organ. The electron transport system (ETS) activity in the muscle increased by 76.25% in fish fed with 1.25% LEO compared to the control, and this parameter showed a high correlation (R2 = 0.87) with the SGR (Chapter 2). The intake of LEO before transport stress (3, 6, 12 and 24 h of duration) resulted in a dissolved oxygen level 17.7% higher than the observed in the control treatment, after 24 h of transport. The blood glucose level remained similar, regardless of feed treatments or transport times. Total antioxidant capacity (ACAP) and lipid peroxidation (TBARS) were measured in the gills, brain, liver, and muscle. After transport for 12 h, fish treated with 1.25% to 10.0% LEO exhibited higher hepatic antioxidant competence (42% to 53%, respectively). Dietary levels at 2.50% to 5.00% LEO played evident protection against lipid peroxidation in the brain, liver, and gills within a 12 h of transportation, punctually reducing the TBARS levels in the muscle (Chapter 3). Seizure-like state induced by pentylenetetrazole (PTZ) was significantly reduced by LEO intake. The electroencephalographic records show less excitability and lower amplitudes in the cerebral wave tracings in fish fed with 5.00% LEO in the diet and exposed to PTZ. For tambaqui treated with 10.0% LEO, this reduction was 80% higher compared to the control group and TBARS levels were reduced by 60% in fish fed LEO in the diet. The neuroprotective effect of açaí was evident in the fish behavior, reducing or abbreviating the signs associated with seizures (Chapter 4). In general, dietary LEO demonstrates functional effects on tambaqui juveniles and, therefore, can be recognized as a potential food additive for this species. To promote fish growth and muscle energetic metabolism, we suggest a dietary inclusion of 1.25% LEO, because is economically feasible with satisfactory effects on food efficiency, growth, and intestinal antioxidant competence. Inclusions of 2.50% to 5.00% LEO in preparatory transport diets are also recommended because they improve water quality after a long transport period and also increase the antioxidant capacity of the liver and reduce lipid peroxidation in all evaluated organs within 12 h of transportation. Finally, anticonvulsant and neuroprotective responses in juvenile tambaqui are possible with the dietary administration from 5.00% LEO.