The purpose of this paper is to investigate the protein enrichment of apple pomace by Gongronella butleri through solid-state cultivation and addition of this material as feed for tilapia fry (Oreochromis niloticus). Factorial experimental design was used for the assessment of culture conditions to determine the effects of the source of nitrogen, initial moisture, and granulometry on the protein enrichment of apple pomace. During culture, the consumption of reducing sugars and the production of soluble protein were determined. The best conditions obtained were with urea (5% w/w), initial moisture of 70% and granulometry in the range from 0.85 to 1.70 mm, producing 19.63% of soluble protein. The fry submitted to the diet containing treated apple pomace presented an increase of 44% in body mass, demonstrating that apple pomace biotransformed may represent an excellent food supplement.