THE EFFECTS OF CALCIUM LACTATE ON GROWTH PERFORMANCE AND DIGESTIVE ENZYMES ACTIVITY OF RED DRUM Sciaenops ocellatus
Organic acids (acidifiers) promote the activation of pepsin and pancreatic enzymes secretion by reducing the pH in the stomach and small intestine, thereby increasing digestion capability in a variety of terrestrial species. Additionally, acidifiers have been shown to improve fish performance by increasing the availability of some dietary nutrients. Hence, it seems reasonable to use this type of product as additives to improve fish diets containing plant feedstuffs. With this in mind, the objective of this study was to determine the effects of calcium lactate (CaL) on growth performance and digestive enzymes activity in juvenile red drum.
A basal diet was formulated to meet the red drum's nutritional requirements, with crude protein set at 40% and provided equally by menhaden fishmeal and dehulled, solvent-extracted soybean meal. Experimental diets were prepared by supplementing the basal diet with 1.5% or 3.0% CaL in place of cellulose. One hundred and eighty juvenile red drum (initial average weight of 8.01 ± 0.29 g/fish) 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 (5% of body weight), twice daily, for 8 weeks. At the end of the feeding trial, growth performance indicators were obtained (weight gain and feed efficiency) and four fish per aquarium were euthanized to measure pH of the stomach contents and digestive enzymes activity in the stomach, anterior and posterior intestine at 6 hours after feeding.
Results showed that the pH of the experimental diets was slightly lowered by the addition of CaL (5.95 - basal diet; 5.79 - CaL 1.5%; 5.70 - CaL 3.0%). The pH of the stomach contents was found to be significantly lower at 2 hours after feeding only in the 3.0% CaL treatment (4.55 - basal diet; 4.54 - CaL 1.5%; 4.30 - CaL 3.0%). No significant differences were found in weight gain and feed efficiency between CaL treatments and the basal diet, regardless of CaL increasing the activity of several digestive enzymes in different digestive tract sections at 6 hours after feeding (Table 1). This increase in enzyme activity could be, as reported before for terrestrial species, possibly due to a pH reduction in the digesta, thereby increasing pepsin activity in the stomach and secretin levels in the intestine, which stimulate pancreatic enzymes secretion. The results showed that CaL can increase the activity of digestive enzymes in juvenile red drum although no significant effects on growth performance were found.