Abstract
Background:
There is no evidence of peptides-probiotics symbiosis as supplements in aquafeeds.
Aim:
To evaluate the effect of peptides and probiotics supplementation via diet on blood parameters and growth performance of juvenile P. brachypomus, an Amazonian fish, during the growth-out phase.
Methods:
120 juvenile P. brachypomus (242.77 g) were placed into twelve 200-L tanks (10 fish/tank), housed in an indoor open system with constant water renovation (flow rate:1.50 L/min). The experiment used a completely randomized design with a 4×5 factorial arrangement [4 doses of supplementation (CD: commercial diet; PepD: CD+1.50% of peptides per CD weight; ProD: CD+40.00 mL of activated probiotics per kg of diet (Lactobacillus spp., Rhodopseudomonas spp., Saccharomycetes spp.); PepProD: CD+Pep+Pro); 5 sampling times (0, 2nd, 4th, 6th, 8th week); n=3]. Fish were fed twice a day at a feeding rate of 1% of body weight. At each sampling time, blood was collected and fish were measured for growth performance analysis. Data was analyzed by using two-way ANOVA and Tukey’s test (p<0.05).
Results:
The values of hematocrit (18.31%), leukocytes (1,216.67 mm3), neutrophils (81.27%), lymphocytes (18.73%), albumin (1.08 g/dL), relative growth rate (1.002%/day) and the Fulton allometric condition factor (2.03) remained constant throughout the experiment (p>0.05). Plasma glucose decreased for all fish in the 2nd week (59.56 mg/dL); then, that level increased in fish fed with the CD (89.00 mg/dL), while fish fed with PepD, ProD and PepProD showed constant values (57.22 mg/dL). The plasma protein levels were constant in fish fed with the PepD and PepProD, (p>0.05), while fish fed with the CD and ProD showed non-constant and higher values. At the end of the trial, fish fed with the PepProD showed the highest weight gain and the lowest feed conversion rate (39.66 g; 0.97).
Conclusion:
It is possible to maintain the stability of plasma glucose and plasma protein by supplementing diets with peptides, but the peptides-probiotics symbiosis administrated via diet contributes to maintain the stability of plasma glucose and plasma protein and to improve the growth performance of juvenile P. brachypomus during the growth-out phase.

Key words: Amazonian fish farming, Neotropical fish, Paco, Plasma glucose, Plasma protein