Resumo

VALBUENA-VILLARREAL, Rubén D  e  VASQUEZ-TORRES, Walter. Body weight is inversely associated with ammonia excretion in red tilapia (Oreochromis sp). Rev Colom Cienc Pecua [online]. 2011, vol.24, n.2, pp.191-200. ISSN 0120-0690.

To meet the increasing demand for fish, aquaculture has expanded through intensive farming that requires large amounts of feed. This can cause environmental and economic difficulties because fish can only retain 20 to 30 % of the ingested nitrogen (N). The remaining fraction is excreted as ammonium and can accumulate in water, thus becoming detrimental to fish performance. This experiment used red tilapia (Oreochromis sp) to determine the effects of temperature, body weight, and dietary crude protein (CP) on ammonium excretion. A factorial AxBxC design was used to compare total ammonium excreted. Factor A is defined as fish body weight (P). Fish weights were: P1= 100 ± 6.2, P2= 249 ± 4.2 y P3= 498 ± 4.7g. Factor B is defined as dietary protein levels (D1, D2 y D3), and factor C as water temperature (T1 and T2). Increased dietary protein levels, as well as water temperature caused significant increases in ammonium excretion (p<0.05). Body weight showed an inverse relationship with ammonia excretion. The 100 g fish at 26 ºC consuming a 25.6% CP diet excreted 468.8 ± 2.2 g N- NH₄⁺ /day/kg, while 498 g fish under the same diet and temperature, excreted 356.3 ± 1.6 mg N- NH₄⁺ /day/kg. This study suggests that dietary factors and environmental variables can alter ammonia excretion in fish, and thus affect of ammonia toxicity in the surrounding water.

Palavras-chave : ammonium excretion rate; body weight; diet protein; Oreochromis sp; red tilapia; water temperature.

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