Optimum Stocking Density of ‘koi’ Carp (Cyprinus carpio) in Combination with Different Plant Species in an Aquaponic System

To maximize profits from aquaponic system, a high-price ‘koi’ carp (Cyprinus carpio) produced at Sultan Qaboos University was used. This study consisted of two experiments. The first experiment aimed to determine the optimal stocking density of ‘koi’ carp in an aquaponic system. In the second experiment, the optimal density of ‘koi’ carp based on the first experiment was used in combination with tomato, eggplant, and mint as a control from the first experiment. The aquaponic system consisted of 9 pairs of glass tanks; in each pair water was recirculating with the use of a submersible pump. In the first experiment, ‘koi’ carp fry (0.4-0.5 g each) were stocked at 50, 100 and 150 individuals per tank (0.1 m3) in combination with mint and the ornamental plant Petunia. Fish were stocked in tanks with and without plants. Results show that ‘koi’ carp stocked at 100 per tank without plants had significantly better growth (mean final weight of 7.5 g from the initial weight of 0.4-0.5 g). Fish stocked in tanks with plants, ‘koi’ carp at 50 per tank had significantly better growth (mean final fish weight of 5.2 g from the initial weight of 0.4-0.5 g). Survival rate was highest at 50 per tank with or without plants. Mint growth was better in tanks with 50 fish per tank. Petunia had flowers in all treatments. Water quality parameters were within optimal range even at high fish stocking densities. Overall, stocking density of 50 fish per tank can be recommended based on survival data. In the second experiment, 30 ‘koi’ carp juveniles were stocked in all tanks without plants (i.e. 6.5 g, 5.5 g and 6.1 g respectively) for each treatment in combination with mint, tomato, and eggplant. Growth and survival rates of koi (30 fish per tank) in combination with mint, eggplant and tomato were high with a weight gain of 21.3, 17.6, 17.6 g and survival rate of 90%, 95.5% and 87.8%, respectively. The results showed that ‘koi’ can be successfully grown with different plants in an aquaponic system.