Effects of organic acids on growth performance and digestive enzyme activities of juvenile red drum Sciaenops ocellatus

In aquaculture species, organic acids and their salts have been shown to trigger beneficial effects on mineral absorption, nutrient digestibility and growth performance by reducing the pH in the digestive tract through H+ ion deposition. Therefore, the aim of this study was to determine if calcium lactate (CaLac), citric add (CA) and potassium diformate (KDF) can improve growth performance of juvenile red drum (Sciaenops ocellatus) and if improved performance is in part due to an increase in digestive enzyme activities. A basal diet was formulated to contain 40% crude protein and six experimental diets were prepared by supplementing the basal diet with 15% or 3.0% CaLac, 0.75% or 1.5% CA and 0.75% or 1.5% KDF. One hundred eighty juvenile red drum were stocked in 110-L glass aquaria (20 fish/aquarium), and diets were fed to fish in triplicate aquaria at a rate approaching apparent satiation, twice daily, for 8 weeks in two separate trials. At the end of each feeding trial, growth performance indicators were obtained and four fish per aquarium were euthanized to measure pH of the digestive tract contents as well as to evaluate the digestive enzyme activities. The pH of the experimental diets was lowered by the addition of 0.75% CA (pH 5.63), 1.5% CA (pH 536) and 1.5% KDF (pH 5.79) when compared with the basal diet (pH 6.15). Moreover, the pH values of the stomach contents were correlated with the pH of the experimental diets. Additionally, based on the weight gain results, it seems that organic acids at a 1.5% dose can improve growth performance in juvenile red drum, although only the weight gain in the 1.5% CA treatment (1547%) was significantly higher than the basal treatment (1357%). This enhanced performance may be in part due to an increment in the activity of digestive enzymes, because pepsin activity, pancreatic enzyme activities (trypsin and lipase) and intestinal enzyme activities (leucin-aminopeptidase and phosphatases) were higher with the inclusion of organic acids in the diet. (C) 2014 Elsevier B.V. All rights reserved.