Feeding trial was conducted to compare the growth performance, amino acid profile, nutrient digestibility and hepatic and intestinal morphologies of ( O. niloticus) fed formulated diets containing either fishmeal (FM), soybean meal (SBM), or protein-enriched copra meal PECM® as the main protein source. The diets were fed to fish with an initial weight of 28.86±1.7 g for 118 days in an indoor RAS. T he mRNA expression of peptide amino acid transporters slc15a1a and neutral amino acid transporter slc6a19 were also examined in the anterior, mid and posterior intestine of tilapia .
Results showed that PECM® -fed fish exhibited 50% slower specific growth rate and reduced body condition factor than FM or SBM-fed fish (Table 1) . Although a decrease is also noticeable in other growth parameters measured, these did not vary significantly among the three diets including feed conversion and protein efficiency (p<0.05) . Overall protein digestibility of diets was high (90.90±2.98%) and unaffected by plant ingredients. No diet-related histopathology was detected in the intestine and liver .
It was hypothesized that the amino acid transporters which are responsible for the absorption of digested proteins in the intestine of fish shall be influenced by dietary changes. Results showed that slc15a1a and slc6a19 responded differently to the dietary treatments . A spatial expression in the intestinal length was also observed. The mRNA expression might be associated with the amino acid profile of each dietary protein source.