Farming largemouth bass (Micropterus salmoides) with lettuce (Lactuca sativa) and radicchio (Cichorium intybus) in aquaponics: effects of stocking density on fish growth and quality, and vegetable production

The present study assessed the effects of two initial stocking densities (low – LD, 4.23 kg m-3, moderate – MD, 8.05 kg m-3) on growth, health and fillet quality of largemouth bass (Micropterus salmoides), and on yield of lettuce (Lactuca sativa) and radicchio (Cichorium intybus group Rubifolium) produced in a low-tech recirculating aquaponic system. A total of 104 largemouth bass (initial body weight: 236 ± 38 g) were randomly stocked in eight 500 L tanks (four per stocking density) and monitored during a 70-day period. Vegetables yield was similar in LD and MD groups. Lettuce yield (6.33 kg m-2) was in line with typical values, whereas radicchio showed a negligible yield (1.34 kg m-2). Likewise, fish final weight (263 g, on average), specific growth rate (0.17% d-1), feed conversion ratio (2.72), and mortality (4.8%) did not differ between treatments. Fish morphometric indices, slaughter results and fillet quality were not affected by stocking density. In conclusion, the production of lettuce was successful in the tested system, whereas the production of radicchio did not achieve satisfactory results. Growth performances of the largemouth bass were poor and further investigations are required to optimize the rearing of this fish species in low-tech aquaponic systems.