UVI Research and Technology Park

Aquaponic Systems

The UVI Aquaculture Program has developed a commercial-scale aquaponic system that produces 5 MT of tilapia annually (harvest at 6-week intervals) and a variety of vegetables (harvest lettuce weekly or as required for other crop types).

Principles of aquaponics - by Dr. James Rakocy

  1. Use good construction materials
    1. Fiberglass is best but expensive
    2. Round fish rearing tanks are preferred over rectangular tanks as they are stronger and self-cleaning.
    3. Hydroponic tanks can have concrete walls with HDPE liners.
  2. Use a feeding rate ratio for design calculations
    1. Feeding rate ratio is the daily amount of feed per unit of plant growing area.  The optimum ratio for raft hydroponics: 2-3 oz/yd2/day (60-100 g/m2/day).  Keep feed input relatively constant by staggering stocking and harvest of each fish cohort.
  3. Remove solids
    1. At least 25% of feed given to fish becomes solid waste, based a dry weight. The wet weight of sludge is much greater
    2. Remove solid waste before it enters the hydroponic component. Solids adhere to plant roots, create anaerobic zones and affect water and nutrient uptake and nitrifying bacteria. Decomposing solids consume oxygen and produce ammonia
  4. Supplement with calcium, potassium and iron
    1. Plants require 13 nutrients for growth. Fish feed supplies 10 nutrients in adequate quantities.
    2. Generally, supplement with Ca, K and Fe.
      1. Add Ca and K as bases – Ca(OH)2 and KOH
      2. Add Fe as a chelated compound or foliar spray
  5. Ensure good aeration
    1. Fish, plants and bacteria require adequate dissolved oxygen (DO) levels for good health and growth.
    2. DO levels of 5 mg/L or higher should be maintained in the fish rearing tank and in the water surrounding plants roots.
  6. Be careful with aggregates
    1. Aggregates such as pea gravel, sand and perlite are excellent media for growing plants.  However, organic matter generated in aquaponic systems can clog aggregate media and channelize the flow. Clogged areas become anaerobic, killing plant roots.
    2. Dissolved organic matter and ammonia promote the growth of bacteria which can clog aggregates.
  7. Oversize pipes
    1. Use oversized pipes to reduce the effects of biofouling. Growth of filamentous bacteria in pipes restricts the flow. Biofouling can even restrict water flow in 4-inch drain lines from fish tanks, causing water levels to rise.
    2. Spaghetti tubes for water delivery to individual plants will most likely clog.
    3. Pipes downstream from solids removal component are less likely to clog.
    4. Lower water temperatures reduce biofouling 
  8. Use biological control
    1. Pesticides must not be used to control insects and plant diseases because they are not approved for fish culture.
    2. Therapeutants for treating fish parasites and diseases should not be used because they may harm beneficial bacteria and vegetables may absorb and concentrate them.
    3. Biological control methods are the only option for controlling insects and diseases.
    4. Use hardy fish and best management practices to prevent fish disease and parasite problems.
  9. Ensure adequate biofiltration
    1. In a raft aquaponic system adequate biofiltration occurs in the hydroponic component. When the optimum feeding rate ratio is maintained, there is excess waste treatment capacity.
    2. In aquaponic systems using Nutrient Film Technique (NFT) there is less surface area for nitrification, and a separate biofilter is needed.
    3. Separate biofilters are used when fish require excellent water quality
  10. Maintain adequate exchange rates
    1. Rearing tank – 1 hour (UVI system – 1.37 hours)
    2. Clarifier – 20 minutes
    3. Deep flow hydroponics channels – unimportant as long as they are aerated
    4. Unaerated channels must have a faster exchange rate
  11. Control pH
    1. Nitrification is more efficient at pH 7.5 or higher and practically ceases at pH values less than 6.0. Nitrification is an acid producing process that continually decreases pH. pH must be measured daily, and base [Ca(OH)2 and KOH] must be added to neutralize the acid.
    2. pH affects nutrient solubility. The optimum pH for nutrient solubility is 6.3-6.5.
    3. In aquaponic systems, pH 7.0 is recommended as a compromise.
  12. Ensure power backup
    1. Install generator with an automatic transfer switch. Obtain a monthly service contract. Schedule weekly automatic generator exercise.
    2. Keep generator topped off with fuel. Install a phone alarm system.
    3. Have a smaller mobile generator that can run key aeration systems. Manually exercise the second generator and keep it fully fueled.