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Wilson Massamitu Furuya*, Sidnei Klein, Wilson Rogério Boscolo, Aldi Feiden, Altevir Signor, Mariana Michelato and Valeria Rossetto Barrivera Furuya
*Animal Science Post graduating program, State University of Maringá (Permanent Professor)- State University of Ponta Grossa (Associate Professor), Paraná, Brasil,

Pacu is an omnivorous and freshwater fish species whose farming is rapidly growing in South America, where culture have been also developed in intensive net cages. Methionine is usually the first limiting amino acid in soybean meal-based diets and plays an important role on growth, feed efficiency and body composition of fish. The present work was designed to determine de dietary methionine on growth performance, body composition, muscle development and hematological responses.

Pacu Piaractus mesopotamicus (n=300; 6.8±2.3g initial weight) were randomly stocked into 15 1m3 (1 x 1 x 1m) net cages each at 20 fish per cage. Five extruded isocaloric (3,250 kcal kg-1 of digestible energy) and isoproteic (32% of crude protein; as feed basis) diets containing 0.40, 0.55, 0.70, 0.85 and 1.00% methionine were  hand fed until apparent satiation four times a day, seven days a week, during 105 days. At the end of the feeding trial, five fish from each cage were collected, pooled and stored at −20 °C for subsequent proximate analysis, four fish per cage were collected for whole body compositions, three fish for muscle morphometric analysis and three fish for haematological responses. All data were subjected to analysis of variance and the best level of dietary methionine for each variable was estimated by linear (Y=a+bx) or second order polynomial regression analysis (Y=a+bx+cx2). Growth performance and whole body composition of fish fed graded levels of methionine are shown in Table 1. It was observed predominance of hyperplasia process in muscle of pacu fingerlings.

No effects of fish fed graded levels of methionine on whole body humidity, crude protein and ash were observed. Haematological responses were not affected by fish fed graded levels of methionine. Based on second-order regression analysis of weight gain, feed conversion ratio, protein efficiency ratio and whole body lipid contents, the dietary methionine were estimated at 0.67, 0.69, 0.67 and 0.69%, respectively.

It was concluded that the dietary methionine requirement of fingerling pacu is 0.67%.

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