EFFECT OF FEEDING FREQUENCY AND FEEDING RATE ON GROWTH AND PLASMA METABOLITES OF JUVENILE NILE TILAPIA

Feeds represent a major cost in aquaculture systems and excess feed can promote deterioration of water quality and reduce nutrient utilization by fish. Optimizing feed management to improve nutrient utilization is a crucial key to match fish growth and feeding costs. Thus, the aim of this study was to evaluate a possible interaction between on growth, nutrient utilization, and body composition of juvenile Nile tilapia. Groups of 26 fish (6.57 g ± 0.10 g) were randomly distributed in 24 experimental units, following a completely randomized design in a factorial arrangement. We tested 1) three feeding frequencies (FF): two, four, and six times a day and 2) two feeding rates (FR): restricted or apparent satiation, totaling six dietary treatments, set up in quadruplicate. The feeding trial, run at 28ºC, lasted 51 days and fish were weighed every 12 days to monitor growth and to establish feed allowance. Blood was collected from the caudal vein of three fish from each tank. Blood glucose was verified immediately whereas the plasma metabolites (total proteins, TP; triglycerides, TG, and cholesterol, CHL) were measured after blood centrifugation at 6000 rpm for 15 min in freeze-stored plasma. All metabolites, except glucose, were measured by enzymatic colorimetric analysis using commercial kits (Labtest Diagnóstica SA, Lagoa Santa, Minas Gerais, Brazil: Cholesterol Ref 76; Triglycerides Ref 87; Total proteins Ref 99). There was no interaction between FF and FR; however daily weight gain (DWG) and specific growth rate (SGR) were 56% and 19% higher in fish fed at apparent satiation, respectively, when compared to fish fed at the restricted regime (Table 1). On the other hand, fish fed at the restricted regime had better protein retention rate (PRR) and feed efficiency (FE) was 14% higher.

Blood TG and glucose were affected by FR: fish fed at apparent satiation presented highest TG (103.95 mmol L⁻¹) and glucose (60.81 mmol L⁻¹) when compared to fish fed at the restricted regime (76.45 mmolL⁻¹ and 55.93, respectively). However, both FF and FR did not affect neither TP or CHL in Nile tilapia. We hypothesize that at high feeding rates fish tend to use protein less efficiently, as shown by the lowest protein retention, when excess dietary protein is probably catabolized to yield energy. Therefore, Nile tilapia fed at the restricted feeding regime optimized their digestion process. Nutrient digestibility and digestive enzyme activity data are under analysis to confirm that hypothesis.

Acknowledgments: Evonik Nutrition and Care GmbH (Essen, Germany), CAPES-Brazil, CNPq-Brazil, Nicoluzzi Rações Ltda (Penha, Brazil), Kabsa Exportadora S.A (Porto Alegre, Brazil).