Fish feed is a highly variable recurring expense for aquaponic farmers. Small farmers are more susceptible to price instability as they commonly pay full retail prices for feed. Financially viable aquaponic businesses require maximizing output while minimizing expenditures. Since fish feed is the primary nutrient input for both fish and plant growth, it is important that the “feed to plant ratio” is sufficient but also economical. The standard loading rate for most aquaponic systems is 60 grams of feed/m2 plant area/ day (g/m2/day). However, it is unclear if this loading rate is the most cost effective.
This study compared a range of feed loading rates for aquaponics. Utilizing six replicated systems, a range of “feed to plant” ratios were evaluated in terms of total biomass production of Bibb lettuce, Lactuca sativa var. capitate, over three production cycles (61 days). Nile tilapia, Oreochromis niloticus, were fed at loading rates of 15, 30, 45, 60, 75, and 90 g/m2/day based on the growing area of the hydroponic unit (2.7 m2).
Using the average plant biomass (g) from two production cycles, a significant polynomial regression was developed to predict the expected plant biomass based on a set feed rate. (Figure 1). Results indicate that 60 g/m2/day will result in the highest plant biomass. A partial budget analysis was then used to compare the projected plant/feed relationships. Even with slightly lower plant production, loading rates of 15, 30, and 45 g/m2/day increased annual profits compared to the Control (60 g/m2/day). This model indicates that 30 and 45 g/m2/day may slightly lower plant production but could be more cost effective overall.