Are artificial semi-dry wetlands efficient in wastewater treatment from different fish densities and for lettuce production?

This study aimed to determine artificial semi-dry wetlands’ performance to wastewater treatment from fish farming and Lactuca sativa production in an aquaponics system. This trial model observed the effects of different stocking biomass on the growth rate of Colossoma macropomum and yield of two L. sativa varieties. A factorial design consisting of three fish density treatments in quadruplicate and two Lettuces variety was used. Nine hundred and sixty fingerlings with 8.35 ± 0.91 g were stocked at three stocking biomass treatments in quadruplicate: 40 fingerlings or 334 g m−3; 80 fingerlings 668 g m−3; 120 fingerlings or 1002 g m−3. Delice American Lettuce and Purple Crested Lettuce were cultured in the semi-dry wetlands. The final mass (g), consumed food, feed conversion ratio, and yield of fingerling were statistically different between the tested densities, but survival did not. The artificial semi-dry wetlands were efficient on water treatment and the recovery of nutrients in all fish densities trials, and it has potential as support for lettuce production. The recovery of nutrients was shown on the increment of the number of leaves, total fresh mass (g), and lettuces yield by area (kg m−2) in both varieties of plants tested. Precocious flowering in 30% of lettuce varieties, incidence of mealybug and whitefly, temperature and deficiency of calcium and magnesium were factors that may have compromised the full lettuce development. The aquaponics system efficiently treated the fish effluent at the densities tested, being appropriate for fish farming and lettuces production.