Plant secondary metabolites are more and more commonly used as functional additives in aquafeeds. Such a process is driven by the market demand for natural products. Citrus extracts are among the most studied extracts for aquaculture. The present study was undertaken to study the effect of graded inclusion levels of a standardized citrus extract in the feed of Nile tilapia.
The Aquaculture Laboratory team of the Federal University of Vale do São Francisco held a trial with 360 Nile tilapia juveniles (mean initial weight = 12.8 ± 0.17 g). After a two-week acclimatization period, fish were divided into 6 groups containing 3 replicates each, where each group received a specific diet. Feeds used in this trial contained different doses of Nor-Spice AB® (Nor-Feed, France): 200 ppm, 400 ppm, 800 ppm, 1,600 ppm and 3.200 ppm (Control, NS200, NS400, NS800, NS1600, NS3200 respectively). Growth parameters were recorded after 60 days. Blood sample were taken on 8 fish in each tank after 60 days.
At the end of this trial 30 fishes of each treatment have been selected to be experimentally infected with intraperitoneal injection of locally available strain of Aeromonas hydrophila (inoculation with 0.2ml of a 1*10-7 CFU/ml solution). Mortality of the fish were then analyzed for 8 days.
Results show a positive effect of the increasing inclusion of NSAB on growth. FCR is influenced with the highest dosage inclusion rate.
Blood analysis show the product increases total protein, cholesterol and hemoglobin. Survival after the challenge with A. hydrophila was also positively influenced by the increased inclusion rate of the citrus extract.
Our results demonstrate the positive effects of the graded inclusion of a standardized citrus extract on zootechnical and hematological parameters when fed to juvenile Nile tilapias grown in unchallenging conditions. They also underline its interest when fish are challenged with a pathogenic bacteria