Further Observations on a Fish Production System that Incorporates Hydroponically Grown Plants

Water temperature was elevated and maintained in two of three fish production systems which incorporated biofiltration and hydroponics. Channel catfish (Ictaluruspunctatus) were stocked in indoor fish tanks and fed to satiation once daily. Tomatoes (Lycopersicon esculentum) were planted in outdoor hydroponic tanks. The study was conducted during the 1979 growing season. Afternoon water temperature averaged 25 ø C in the control system and 28 ø C in both experimental systems. The temperature in the control unit varied with the ambient diel cycle, whereas the temperature in the two experimental units remained constant. The mechanics of the system were satisfactory and the plants showed no adverse effects associated with the heated water. The total fruit yield (in kilograms per plant) was similar in all systems: control, 8.9; experimental A, 9.1; and experimental B, 9.1. Growth of the yearling fish was enhanced by the constant elevated temperature. The respective average rates of growth from 15 May to 22 June in the control system and experimental systems A and B were 0.96, 1.47, and 1.06 g/day per fish. Lewis et al. (1978) reported on a fish production system in which water quality was maintained by biofiltration and plants were grown hydroponically. Additional evaluation of this system, and a new design of the system, are given in Lewis et al. (in press). In the present study we continued the evaluation of the new design and examined the effects of constant elevated temperature on channel catfish (Ictalurus punctatus) and tomatoes (Lycopersicon esculentum). The latter consideration is of particular importance, since channel catfish exhibit maximum growth at 28 to 30øC (Andrews et al. 1972). However, there is some question concerning the effects of constant elevated temperature on the performance of tomatoes, which are superior plants for use in such a system. Went (1944) reported that both better growth and fruit set were produced in tomato plants by warm days and cool nights than by constant temperature. Also, Went (1957) and Resh (1978) suggested that the optimal temperature for growth of tomatoes might vary with the stage of plant development. Methods find Materials The system used in the present study included a 190-L fish culture tank equipped with an agitator for aeration (Fig. 1). The indoor fish tank was coupled to a revolving-plate biofilter modeled after the design of Present address: Environmental Research and Technology, Inc., 1716 Heath Parkway, Fort Collins, Colo. 80524. Lewis and Buynak (1976). The biofilter consisted of three compartments (total surface area, 2.7 m 2) and was connected to a sedimentation-flotation tank which, in turn, was linked to a pair of outdoor hydroponic tanks that were filled with gravel (5 10 mm size) and positioned at different levels. Each hydroponic tank measured 3.05 m long, 0.51 m wide, and 0.25 m deep. The lower tank was connected to a water-equalizing reservoir which compensated for water lost through evaporation and transpiration. The total volume of the system was about 750 L.