We investigated the effect on melon fruits of "fish water" alone or in combination with a supplement of synthetic fertilizers in a nutrient solution or foliar application of Ca(NO3)2. These treatments were compared with a traditional soilless system with synthetic fertilizers and no reuse of the nutrient solution. The results show that the treatments with recirculation of fish water and with the foliar supplement yielded fruits of greater weight and size but with reduced lightness and lower concentrations of proteins, NO3-, K+, and total amino acids. The supply of synthetic nutrients to the roots or leaves caused a reduction in the sugar concentrations and the antioxidant activity of these fruits. The use of fish water (alone or with an amendment) increased spermine and putrescine with respect to the traditional soilless crop management. The results for these bioactive compounds in melons should be considered for maintenance of health with age.
Keywords: antioxidant activity; aquaponics; color; melon (Cucumis melo L.); mineral composition; nitrate; nutrient recycling; polyamines; sugar amino acids.