Sport fish production and productivity relationships in reclaimed domestic wastewater.

Abstract

The purpose of this study was to evaluate the suitability of reclaimed domestic wastewater for a sport fishery. The water was reclaimed by a tertiary treatment of sand filtration. The fish tested were Channel catfish, Ictalurus punctatus, Rainbow trout, Salmo gairdneri, and Malacca Tilapia hybrids. The major objectives were to establish survival rates, growth rates, stocking schedules, and maximum stocking densities for these fish in an unusual and highly productive environment. Less than 1% survival occurred in five trout experiments and in one catfish experiment. An important cause of mortality was low sunrise oxygen tensions resulting from respiration of dense phytoplankton blooms which were stimulated in part by high (14 mg/l) average inflow orthophosphate concentrations. When fish survived, production was high, The total yields of acceptable Channel catfish and Tilapia were 383 and 397 Kg per hectare, respectively, Chironomus larvae, the predominant food organism, comprised 90 of the estimated annual benthic production of 14,180 Kg per hectare. Zooplankters, although abundant, were not an important source of fish food because of their small size, Phytoplankton productivity averaged 10.2 gm O₂ per m³ per day. The present waters, although highly productive, cannot be expected to support a dependable fishery because occasional unfavorable oxygen conditions are likely to reoccur.