Stability and phosphorus leaching of tilapia feed in water

EnglishThe present research aimed to investigate the stabil¬¬ity 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 highest flotation 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 portuguesO 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. Utilizaram-se 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 °C. Todas as dietas foram avaliadas quanto a condutividade eletrica da agua, turgidez, lixiviacao de materia mineral, flotacao de pellets e lixiviacao total do fosforo. Apenas a turgidez e a flutuacao dos pellets variaram com as diferentes fontes de fosforo nas dietas. A dieta MBM apresentou a maior turgidez de pellets. As dietas PM, AM e CBM apresentaram a maior flutuacao de pellets. A lixiviacao do fosforo total teve um efeito linear com o aumento do tempo de exposicao, resultando em maior liberacao de fosforo na agua. A lixiviacao de materia mineral apresentou interacao entre fontes de fosforo e tempos de exposicao das dietas, com efeito linear para a dieta TM. As dietas PM, AM e CBM apresentam as menores concentracoes de efluentes em relacao a dieta TM. Esses resultados revelaram que dietas formuladas com diferentes fontes de fosforo apresentam acoes distintas na agua em relacao ao potencial poluidor. Palavras-chave: aquicultura; aquafeed; impacto ambiental; lixiviacao do fosforo; qualidade da agua