Effects of composting worm species and abundance on Lettuce and barramundi Lates calcarifer production in an Aquaponics system

In aquaponics, substrate-based plant culture is common because it provides substantial root support and allow the farmer to regulate root moisture - benefiting crops yields. One of the major issues in these systems is the deposition of feed waste, fecal material, and decomposing roots in the substrate, potentially causing water quality and disease issues for the plants, beneficial bacteria and fish. Composting worms are commonly used to manage the organic matter deposition and are thought to aid in mineralizing the nutrients bound in the waste sediments allowing the plants to metabolize them. Additionally, the production of worms (Vermiculture) is a potential revenue source for aquaponic producers. Although the use of composting worms in aquaponics is common, formal scientific research in this area is lacking. The goal of this experiment is to analyze the effects of composting worm species and abundance for processing wastes in the grow beds as well as production characteristics for fish and plants in a substrate-based aquaponics system.

Barramundi (Lates calcarifer) and bibb lettuce seedlings (8 per culture unit) were stocked into one of three replicated 720-L aquaponic systems, each containing four plant culture units. The plant culture units measured 75 cm x 80 cm x 20 cm and were filled to a depth of 17 cm with rounded river pebbles (pea gravel) measuring 0.5 to 1.5 cm diameter. Water was pumped to the plants hourly from 06:00 to 18:00 for 15 minutes intervals (controlled via timer).  Lettuce production data (i.e. number and biomass) was collected throughout the culture period.  

Composting worm treatments consisted of a control (no worms), Red Wiggler (Eisenia fetida) worms and Red European Night Crawlers (Eisenia hortensis). Sediment deposition and processing were analyzed in each plant culture unit between crops (approximately monthly).  Nutrient analysis of the sediments, effluent water, and plant tissue was conducted.  At harvest the remaining worms were enumerated and weighed to assess biomass gain. Potential value to the farmer will be discussed.