Comparing water quality/bacterial composition and productivity of largemouth bass Micropterus salmoides juveniles in a recirculating aquaculture system versus aquaponics as well as plant growth/mineral composition with or without media

Abstract

Aquaponics is the integration of farming fish with plants where the excreted nutrients from fish are taken up by plants. Thus, aquaponics may enhance aquaculture sustainability and productivity. In this study, largemouth bass Micropterus salmoides juveniles were cultured in a recirculating aquaculture system (RAS) or aquaponic system for two months. Each system was identical, but within the aquaponic system, lemongrass and spring onion were cultured with or without gravel in a 2x2x2 factorial design. After 2 months, there was no difference in the survival, growth, feeding efficiencies or condition indicator of fish in either system, despite nitrate-N being consistently higher in RAS, particularly from day 48 onwards. Water iron and total phosphorus were similar among each system. Bacterial diversity was lower in RAS, but Streptomyces was only detected in RAS which contributes to off-flavors. Spring onion wet weight and leaf width values were significantly greater when cultured with media but had significantly shorter roots. Lemongrass leaf length and width values were also significantly greater when cultured with media, but had significantly shorter roots. There were various significant main effects on the mineral composition, particularly for iron. Generally, both zinc and iron accumulated in the roots of both plant while potassium was higher in the leaves. Spring onions were a richer source of potassium and calcium than lemongrass. Magnesium and iron were generally higher in the leaves and roots when cultured without media and might be due to the roots having a greater surface area for nutrient uptake. Overall, M. salmoides is a suitable high value fish species to grow with aquaponics while using media enhanced the productivity of both plant species as well as their magnesium and iron contents. The absence of Steptomyces in the aquaponic system may have implications to post-harvest fish quality that should receive additional attention.