Expressão dos genes relacionados ao crescimento muscular e frequência das células produtoras de muco de brânquias e intestino de tilápias do Nilo alimentadas com níveis crescentes de treonina

Abstract

Two experiments were carried out to determine the dietary threonine requirements for Nile tilapia during two rearing phases through the growth performance, muscle growth, expression of MyoD and Myogenin, body composition, hematological evaluation and assessment of mucus production in the epithelium gill and intestinal mucosa. In the first experiment, 216 Nile tilapia (10.77 ± 2.54 g) were distributed into 18 fiberglass aquarium of 250 liters each. Fish were fed to with extruded isoproteic (35.88% crude protein) and isocaloric (3.420 kcal.kg-1 gross energy) diets containing 9.05, 12.34, 16.95, 21.21, 24.54 and 27.95 g.kg-1 threonine. No effects of graded level of dietary theronine on growth performance and body composition were observed. Fish fed 12.34 g kg-1 histidine showed increased muscle growth process by hypertrophy, higher Myogenin expression and higher mucus-secreting cells. It was concluded that 9.05 g.kg-1 threonine meet the dietary requirment for growth performance but maximized mucus-secreting cells occurs in fish fed 12.34 g kg-1 threonine. In the second experiment, 270 Nile tilapia (54.5 ± 1.7 g) were distributed into 18 floating net cages of 1,5m3 each. Five extruded diets containing 14.1 MJ kg-1 gross energy and 293.6 g.kg-1 crude protein containing 8.6,10.7, 13.6, 15.6 and 18.1 g kg -1 threonine were used. Fish fed 10.7 g kg-1 threonine showed improved weight gain, protein efficiency ratio, feed intake, muscle growth enhanced by muscle hypertrophy and expression of MyoD and higher synthesis of mucus-secreting cells in gills and intestinal tissues. It was concluded that the threonine level of 10.7 g kg-1 is appropriate to ensure productive performance, muscle growth and maximize mucus-secreting cells of Nile tilapia.