Arapaima gigas is the world’s largest scaled freshwater fish, which is native to the Amazon basin and belongs to the most basal branch of extant Teleostei. Efforts are being made in its farming in order to reduce the feeding costs, since A. gigas is a strictly carnivorous species that uses high-protein aquafeeds. High-fat diets up to species tolerance limits may improve growth performance and protein utilization through the protein-sparing effect provided by dietary lipids. The objective of the study was to evaluate the effect of high-fat diets in the hematological and biochemical parameters of juvenile A. gigas, since blood parameters are significant indicators for estimating the health status of farm animals.
Five isoproteic (451.74 g/kg of CP) diets were formulated to contain increasing lipid levels as 6%, 10%, 14%, 18% and 22% and, consequently, increasing gross energy to crude protein ratios (9.73; 10.12; 10.57; 10.93; 11.39). Treatments were defined by the dietary lipid levels as 6DL; 10DL; 14DL; 18DL; 22DL. A completely randomized design was applied with 5 treatments (diets) and 4 repetitions each. 600 juvenile A. gigas (80.03±10.46 g; 21.81±1.01 cm) were distributed in twenty 500-L tanks (30 fish/tank), in an indoor open system. The fish were fed to apparent satiation, four times daily, for 60 days. At the end, the hematological and biochemical parameters were evaluated by one-way ANOVA and Tukey test (p<0.05).
Values of hemoglobin, RBC, MCV, MCH, WBC, neutrophils, lymphocytes, triglycerides and cholesterol in juvenile A. gigas were not affected by different dietary lipid levels (p>0.05). Fish fed with 6DL presented the lowest hematocrit value and the highest MCHC (p<0.05), while those parameters were constant in fish fed with 10DL to 22DL (p>0.05). In fish fed up to 14DL, the plasma glucose content was similar and higher than those reported in fish fed with 18DL and 22DL. The lowest content of plasma protein was showed in fish fed with 18DL.