Submitted to: Aquaculture Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/25/2004
Publication Date: 11/24/2004
Citation: Riche, M.A., Garling, D.L. 2004. Effect of phytic acid on growth and nitrogen retention in tilapia Oreochromis niloticus. Aquaculture Nutrition. 10:389-400. Interpretive Summary: Soybeans are considered one of the most promising alternatives to fish meal in aquatic animal feeds. However, soybeans contain anti-nutritional factors that reduce the availability of nutrients. One such anti-nutritional factor is phytic acid. Phytic acid is a compound found in many cereals and legumes that allow the plants to store phosphorus. Phytic acid is known to bind with proteins in feeds making the proteins unavailable to the animal. This has been demonstrated in rainbow trout and Atlantic salmon. Therefore we conducted two experiments to determine the effect phytic acid has on the availability of proteins in soybean based diets fed to tilapia. In the first experiment we evaluated 8 diets utilizing soybeans that either had phytic acid in them, or had the phytic acid destroyed prior to using them in the feed. The soybeans were added to make 25, 50, 75, or 100 % of the total dietary protein. In the second experiment tilapia were fed fish meal diets with different concentrations of purified phytic acid added to them. Following the first experiment two different models were applied to the growth data to estimate the maximum amount of soybeans that could be added without compromising performance. The models suggest phytic acid containing soybeans should be limited to 38 % of the total protein, and that destroying the phytic acid further reduces the limit to 17 % of the protein. Growth and efficiency declined when the diet contained soybeans without phytic acid beyond 25 % of the total protein. However, by using soybeans with phytic acid remaining the level could be raised to 75 % of the total protein before growth and efficiency were compromised. The results of the second experiment indicate the addition of phytic acid to the diet does not compromise growth and efficiency at concentrations typically associated with soybeans. Phytic acid does not reduce nitrogen retention in tilapia as it does in rainbow trout and Atlantic salmon.
Technical Abstract: Two experiments were conducted to determine the effect of phytic acid on nitrogen retention in tilapia (Oreochromis niloticus). The first utilized graded levels of soybean meal (SBM) with and without hydrolysis of phytic acid. The second utilized diets containing graded levels of purified phytic acid. In the first experiment, weight gain was 402 - 771 % and inversely related to SBM inclusion beyond 25 % of the crude protein (CP). Broken line and quadratic models were applied to the growth data. The models suggest limiting inclusion to 38 % and 17 % CP for untreated and phytase treated SBM, respectively. The two SBM treatments exhibited similar trends in efficiency parameters. However, significant differences (P<0.05) within treatments appeared when phytase treated SBM surpassed 25 % CP, but not until 75 % CP with untreated SBM. At similar rates of SBM incorporation, apparent net protein utilizations with untreated SBM were significantly higher beyond 25 % CP (P<0.05). In the second experiment phytic acid did not effect efficiency parameters until the concentration was twice that in diets incorporating SBM as 100 % CP. Phytic acid does not reduce nitrogen retention in tilapia, and its removal from SBM appears to decrease nitrogen retention.