Dietary lysine requirements of Colossoma macropomum (Cuvier, 1818) based on growth performance, hepatic and intestinal morphohistology and hematology

This study aimed to determine the dietary lysine requirements of juvenile Colossoma macropomum tambaqui based growth
performance, hepatic and intestinal morphohistology and hematology. Tambaqui were fed with levels of 6.60, 9.72, 12.84,
15.96, 19.08, and 22.20 g/kg of total lysine and those who received 15.96 g/kg dietary lysine showed higher final weight (p=
0.001) and optimized feed conversion ratio (p= 0.001). Morphohistological modifications (presence of fat droplets) were
present in livers of fish fed with low levels of lysine. In the morphohistology of the intestine, the diets influenced the density
of the intestinal, cell layers, height and perimeters of the villi and acid mucin secretion by the goblet cells. In the proximal
intestine, mucosa layer density was greater at the level of 15.96 g/kg (p= 0.001). In the middle intestine, height (p= 0.001)
and perimeter (p= 0.001) of the villi were greater at low levels of lysine (respectively, 9.72 and 12.84 g/kg dietary lysine).
No differences were found for the hemoglobin, hematocrit, erythrocytes, MCV, MCH, MCHC, thrombocytes and leukocytes
differentiated of fish fed with experimental diets (p>0.05). The biochemical responses were affected by the diet, both in
plasma concentration (protein and cholesterol; p<0.05), and in muscle (ash and moisture; p<0.05). In conclusion, the dietary
requirement for lysine for tambaqui juveniles was estimated to be 15.4 - 15.6 g/kg of diet (5.7% –5.8% dietary protein).