Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Renewable Natural Resources

First Advisor

Robert C. Reigh


Crude protein is the most expensive macronutrient, the use of plant proteins and crystalline amino acid supplementation is the next logical step to increase nutritional value of plant-based diets. The goal of this experiment was to determine the effect of coated and uncoated crystalline methionine on growth, body composition, and methionine uptake in Nile tilapia Oreochromis niloticus fed methionine supplements. Two experiments were designed for this purpose: one to study the effect of supplementation on weight gain and body composition, and a second to determine the effect of coating on absorption efficiency and utilization of crystalline methionine. Five isonitrogenous (26% CP), isocaloric (2420 kcal g of protein), purified diets were created by supplementing a methionine (Met) deficient basal diet (MD) at 50% of the dietary requirement. All five diets contained methionine from intact protein and four diets also were supplemented with crystalline methionine at a level of 0.29% (as fed). One diet (CM) was supplemented with crystalline methionine. Another (KCM) contained 0.29% kappa-carrageenan microbound methionine. A third (TM) contained 0.29% microencapsulated tripalmitin methionine, and the final diet (CAP) contained 0.29% cellulose-acetate-phthalate microcoated methionine. In the second experiment diets CM, KCM, and TM were used to determine the effect of coating on Met absorption efficiency and utilization. Each diet contained 7.4 Bq (200 muCi) of labeled 35S-methionine. No significant differences in weight gain, feed conversion ratio, protein efficiency ratio and feed consumption were detected among fish fed the experimental diets. Fillet protein of CAP-fed fish was significantly lower than that from fish fed the other four diets. Tissue lipid content was similar among fish fed MD, CM, KCM. CAP-fed fish showed plasma free-methionine concentrations significantly higher at 6 h after feeding, than fish fed the other diets. Uptake of 35S was significantly higher among fish fed CM and CAP than among fish fed TM. Results suggest that uptake of crystalline methionine was unaffected by coating with CAP, while TM coatings significantly reduced absorption of crystalline methionine relative to uncoated Met. More effective coatings might be used to increase the efficiency of utilization of crystalline methionine in prepared tilapia diets.