Stability and phosphorus leaching of tilapia feed in water/Estabilidade e lixiviacao do fosforo da racao de tilapia na agua

The present research aimed to investigate the stability of pellets and phosphorus leaching of diets formulated for juveniles of Nile tilapia (Oreochromis niloticus), with different sources of phosphorus and different exposure times in water Six diets were elaborated by varying the source of phosphorus (1--dicalcium phosphate (DP); 2--meat and bone meal (MBM); 3--poultry meal (PM); 4-- anchovy meal (AM); 5--tilapia filleting industrial meal (TM); 6--calcined bone meal (CBM)) and, then, were submitted to four exposure times in water (5, 10, 15 and 20 minutes), with three replicates. Thus, 72 aquariums of 30-liters were used, each being an experimental unit. All diets were evaluated for electrical conductivity of water, turgidity of pellets, mineral matter leaching, flotation of pellets, and total phosphorus leaching. Only turgidity and flotation of pellets varied with the different sources of phosphorus in the diets. The MBM diet had the highest turgidity of pellets. The PM, AM, and CBM diets had the highestflotation of pellets. The total phosphorus leaching had a linear effect with the increase of the exposure time, showing a greater release of phosphorus in the water with increase of exposure time. Data showed that PM, AM, and CBM diets had less potential impact on the aquatic environment. Conversely, the TM diet has greater polluting potential. These results showed that diets formulated with different sources of phosphorus exhibit distinct actions in the water, providing different effects on the fish culture environment. Key words: aquaculture, aquafeed, environmental impact, phosphorus leaching, water quality. O presente trabalho tem como objetivo investigar a estabilidade de pellets e a lixiviacao do fosforo na agua proveniente de diferentes dietas formuladas para juvenis de tilapia do Nilo (Oreochromis niloticus), considerando distintas fontes de fosforo e diferentes tempos de exposicao na agua. Para tanto, foram elaboradas seis dietas com variacao da fonte de fosforo (1: fosfato dicalcico (DP); 2: farelo de carne e ossos (MBM); 3: farelo de aves (PM); 4: farelo de anchova (AM); 5: farelo industrial de filetagem de tilapia (TM); 6: farelo de osso calcinado (CBM)), as quais foram submetidas a quatro tempos de exposicao em agua (5, 10, 15 e 20 minutos), com tres repeticoes. Utilizaramse 72 aquarios de 30 litros, sendo cada um deles uma unidade experimental. A agua dentro dos aquarios foi mantida sob constante aeracao e temperatura ao redor de 25[degrees]