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Abstract
An eight-week study evaluated the effects of flow rate and dietary protein on the function of sand and gravel biological filters for ornamental fish production. Forty tiger barbs, Barbus tetrazona, were placed in each of twelve, 38-L tanks. Upflow sand and gravel filters operated at non-fluidization flow rates of 57.5 L/hour and 111 L/ hour were compared. Diets with 32%, 40%, and 42% protein contents were compared. Total Ammonia Nitrogen (TAN) levels were significantly lower in the tanks with 57.5 L/hour filters. TAN levels were also significantly (P< 0.05) affected by dietary protein content. Nitrate levels varied significantly with dietary protein content, but did not vary with different water flow rates. Final nitrate concentrations averaged 10.2 ppm in 42% protein tanks, 16.0 ppm in 40% protein tanks, and 6.0 ppm in 32% protein tanks. Nitrite levels were not affected (P> 0.05) by either flow rate or dietary protein level. Fish growth rate was not affected (P >0.05) by water flow rate, but growth rate was significantly affected by dietary protein levels. Mortality rates were not significantly different (P >0.05) between treatments.