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Palter 23 at low flow rates than those predicted by the model. The model will be most accurate at intermediate flows, which are also the flows at which routine biofitter operations arc likely to be conducted. The model presented in this paper can be used to predict the carrying capacity of submerged biofi[ters, calculate the biofitter volume needed to support different fish loads, and assess the effects of changes in system dimensions and flow rates on biofitter perfor- mance. The basic requirement of the mode! is an initial estimate of ammonia removal from a biofitter of the same type as the one about which predictions wilt be made. A strength of the model is its sim- plicity in terms of computations and input data requirements. The price of simplicity, however, is a possible reduction in accuracy under some conditions as previously discussed. So far, the model has been applied only io experimental biofiltration systems. Further research should emphasize the evaluation of prediction accuracy over changes in feeding rate and the application of the model tofull- sized systems and possibly to other types of biofilters besides sub- merged. It may also be possible to add refinements to the model to further enhance its accuracy. However, substantial increases in com- plexity, especially those requiring the input of difficult-to-acquire data (such as biofilm composition), could reduce the utility of the model to practicing aquaculturists. ACKNOWLEDGMENTS Appreciation is extended to William M. Lewis and Roy C. Heid- inger for providing facilities and support at the Fisheries Research Laboratory, Southern lttinois University at Carbondale. REFERENCES APHA (American Public Health Association), American Water Works Associa- tion, and Water Pollution Control Federation. 1976. Standard Methods for the Examination of Water and Wastewater, 14th ed. American Public Health As- sociation, New York, New York. Brett, J.R., and C.A. Zala. 1975. Daily pattern of nitrogen excretion and oxygen consumption of sockeye salmon (Oncorhyncus nerka) under controlled condi- tions. Journal of the Fisheries Research Hoard of Canada 32:2479-2486. Bovendeur, J., E.H. Eding, and A.M. Henken. 1987. Design and performance of