Feed restriction as a feeding management strategy in Colossoma macropomum juveniles under recirculating aquaculture system (RAS)

This study aimed to evaluate performance, biochemical, hematological and tissue parameters in tambaqui Colossoma macropomum juveniles with initial average weight of 18.0 ± 4.0 g submitted to feed restriction. Three feeding protocols were tested for 56 days: continuous feeding (control); feeding for six days and feed restriction for one day a week (F6R1); and feeding for five days and restriction for two days a week (F5R2). Growth performance was evaluated as weight (W), feed intake (FI), feed conversion ratio (FCR), specific growth rate (SGR) and protein efficiency ratio (PER) at 28 days and from 29 to 56 days of experiment. Blood samples were collected at 28 days (after restriction period in F5R2 and F6R1) and before (at 54 days) and after feed restriction period (at 56 days) to determine hematocrit, hemoglobin, plasma glucose, triglycerides, cholesterol and protein levels. Liver and muscle lipid concentrations, the hepatosomatic index and the mesenteric fat index were evaluated after 28 and 56 days. After 28 days there was a decrease in W, FI and SGR and a better FCR for F5R2, when compared to the control. From day 29 to day 56 there was a decrease in W, FI and a better FCR for F5R2, when compared to the control, while SGR and PER of restricted groups were similar to the control. After 28 days there was a decrease in hematocrit and triglycerides for F5R2, while there was no significant difference in hemoglobin, glucose, cholesterol and protein. Hematocrit was significantly lower in F5R2 group, while there was no treatment, period (54 and 56 days) and interaction between them for hemoglobin concentrations. For glucose, there was an effect of the treatment, as well as an effect of the period but there was no interaction between them. For triglycerides levels there was an effect of treatment, period and interaction between them. Protein and cholesterol levels were influenced only by period and both variables showed an increase in their levels at 56 days, compared to 54 days. After 28 days there was no significant difference for liver lipid levels, muscle lipid and the mesenteric fat index in all treatments; however, there was a decrease in the hepatosomatic index in F5R2. After 56 days there was a decrease in liver lipid levels and the hepatosomatic index with the increase in the restriction period, but there was no significant difference for muscle lipid levels and the mesenteric fat index. Juveniles of C. macropomum submitted to feed restriction for one day a week (F6R1), maintained their body reserves and hematological and biochemistry variables (except for triglycerides at 56 days) unchanged and showed good performance, similar to animals continuously fed for 56 days. However, due to the great heterogeneity of the animals, obtained mainly at the end of the experimental period (56 days), it is recommended to carry out periodic weight classifications for the production of this species in RAS.