This study determined how using monosex Nile Tilapia (Oreochromis niloticus) at different stocking densities can increase the Batavia lettuce (Lactuca sativa) crop production, while adjusting the water effluent flow between fish tanks and sand grow-beds. The experimental design included three replicates for each of the sandponic systems stocked at densities of 100 and 150 fish/m3 with an average initial weight (25.4 ± 2.3 g) for a rearing period of 45 days. Each treatment had three fish tanks (2 m3 water volume per tank), integrated with a one-meter width sand grow-bed (total area 10 m2). The density of Batavia lettuce is 12.5 lettuce/m2. The fish were fed to satiation three times a day using a 30% crude protein (CP) commercial formulated diet. The water quality parameters were monitored daily )dissolved oxygen - DO, pH and temperature were checked daily( and water chemistry parameters were monitored weekly (total ammonia nitrogen - TAN, nitrite, nitrate, potassium, and soluble reactive phosphorus - SRP). In addition, other main culture parameters were monitored (plant/fish biomass growth, fish feed consumption, fish survival, final lettuce/fish production at harvest, water and electricity consumption), while maintaining a flow rate of 1.5 L/min every 2 – 3 hours between fish tanks and sand grow-beds. The water lost through transpiration, evaporation, and periodic flushing was replaced weekly. The water quality parameters in both experiments were within the acceptable range for tilapia and all increased as fish stocking density increased (3.1–5.3 mg/L for DO, 7.2-8.4 for pH, 0.012- 0.029 mg/L for TAN, 0.030–0.034 mg/L for nitrite, 0.001-0.002 mg/L for nitrate, 1.2-3.1 mg/L, potassium, 5.2-5.6 mg/L and SRP, 2.4-4.9 mg/L).
The final weight of fish at harvest was 71.5 ± 3.2 g and 69.2 ± 5.1 g for 100 and 150 fish/m3, respectively. Specific growth rate (SGR) and survival rate was reduced with increasing stocking density, whereas food conversion ratio (FCR) increased at the higher stocking density. Sandponic systems with the lower fish stocking densities (100 fish/m3) performed better than 150 fish/m3. The growth performance of Nile tilapia fingerlings in terms of SGR, survival rate and FCR were significantly influenced by the stocking density. The SGR was estimated at 2.3% and 1.8% at 100 and 150 fish/m3, respectively. The survival rate was 95% and 91% at 100 and 150 fish/m3, respectively. The FCR was reported to 1:1.5 and 1:1.7 at 100 and 150 fish/m3, respectively. The biomass at harvest was 6.8 kg fish/m3 and 8.2 kg fish/m3 at 100 and 150 fish/m3, respectively. The water chemistry with fish in both experiments was significantly different for nitrate, potassium, and SRP in high fish density, which as impacted positively on the mean of plant weight at harvest, 520 gm/lettuce head and 400 gm/lettuce head in 100 and 150 fish/m3, respectively. Also, the presentation will report on the actions needed to achieve efficient production and economic returns.