PRODUCTION OF SPEARMINT Mentha spicata WITH AQUACULTURE EFFLUENTS OF AFRICAN CATFISH Clarias gariepinus IN NORTHERN GERMANY
Mint (Mentha spp.), a fast-growing culinary herb, was described as a plant with a high economic potential for aquaponics production . Species of the genus Mentha (Lamiaceae ) have a high growth potential and are used for industrial and pharmaceutical products such as chewing gum, toothpastes, cosmetics or tea. Though known as a water loving plant, studies with mint under aquaponics conditions are scarce and the combined production with African catfish (Clarias gariepinus ) is relatively new. African catfish is a common recirculation aquaculture fish in Europe, especially in the Netherlands, Austria, Hungary and Germany. In 2017, the production yield of African catfish reached 1,060 t for Germany with continuously increasing quantities, especially in Mecklenburg-Western Pomerania , Northern Germany . The present study evaluated the growth of spearmint (Mentha spicata ) with pure effluent water from aquaculture production of African catfish (Clarias gariepinus) reared under extensive and intensive stocking densities without addition of fertilizer .
The experiment was carried out in the experimental state-of-the-art aquaponics facility FishGlassHouse in Northern Germany from late summer to autumn (27.08.2015- 04.11.2015 ) for 70 days , and African catfish with an initial weight of 275 g. The e xtensive aquaculture unit (EAU) was stocked with 7.6 kg/m³ and 35 fish per tank (n=9) while the intensive aquaculture unit (IAU) had a stocking density of 30.6 kg/m³ and 140 fish per tank (n=9). Fish were fed by automatic feeders with ME‒4.5 44‒14 Meerval (Skretting, France) with 44% crude protein, 14% crude lipid, 22.3% NFE, 10.5% ash, 1.2% crude fiber and 1.6% phosphorus. A total of 1,260 M. spicata were planted on ebb-and-flow tables (3.05 x 1.01 m/table ) in triplicates with a control group supplied with a special low nutrient hydroponics fertilizer solution (1.12 mg/L NH4⁺‒N, 9.61 mg/L NO3‾-N, 5.54 mg/L PO43‾‒P).
Spearmint (M. spicata) grown with effluent water from the IAU showed best growth performance (Table 1). In comparison to EAU, the mint of IAU had a 11.37% better plant height, 1.4 more shoots, 1.9 folds higher leaf area and 13.21% higher fresh biomass. Our results demonstrate the possible production of spearmint (M. spicata) in combination with African catfish (C. gariepinus) in aquaponics . Future experiments must evaluate the quality or the produce in comparison with regular production of mint in classical hydroponics or soil.
