Polyculture of catfish, rainbow trout and Swiss chard in haloponics

The study evaluated the effects of three water salinity levels (0.5‰, 3.0‰, and 6.0‰) on adaptability, growth performance, and carcass traits of black bullhead catfish (Ameiurus melas) and rainbow trout (Oncorhynchus mykiss) in polyculture, as well as on the production of Swiss chard (Beta vulgaris, ssp. vulgaris) in a low-tech and brackish-water aquaponic (haloponic) system composed by 9 independent units. A total of 261 catfish (initial weight 147 ± 22 g) were randomly distributed among the three experimental treatments (three units per treatment; initial stocking density 8.50 kg m-3) and reared for 268 days from September to June. In December, 150 trout (initial weight 153 ± 22 g) were added to the system (initial stocking density 5.06 kg m-3) and reared for 103 days in polyculture with catfish from December to March. During the trial, two cultivation cycles of Swiss chard of “Nostrana” (1st cycle) and “Pugliese” (2nd cycle) varieties were carried out (12 plants m-2, 24 plants per unit). Water salinity did not affect trout final weight (348 g, on average), survival (89.7%), as well as eviscerated carcass (87.5%) and fillet (52.0%) yields. Similarly, no differences were found in catfish final weight (193 g), survival (75.8%), and fillet yield (48.3%), whereas a higher carcass yield was found at 0.5‰ salinity than at 3.0‰ (87.3% vs. 85.2%; P<0.05) with intermediate values for 6.0‰ salinity. The marketable biomass of Swiss chard was 337 g for “Nostrana” and 823 g for “Pugliese” varieties, without differences due to water salinity. In conclusion, polyculture of catfish, trout and Swiss chard is achievable until 6‰ water salinity, therefore increasing the diversification of cultivable species and the resilience of haloponic systems.