Fish manure as a potential feedstock for organic hydroponic nutrient solutions: The effect of fish feed composition and fertilizer amendment on the growth performance of lettuce

The use of nutrient solutions derived from the bioprocessing of organic feedstocks such as waste sludge from aquaculture appears to be a promising alternative to inorganic fertilizer. This study assessed the effect of feed composition (predominantly animal- versus plant-based) of feeds fed to Nile tilapia (Oreochromis niloticus) on performance parameters of lettuce (Lactuca sativa var. Bonarda RZ) grown in nutrient solutions based on batch-wise aerobically remineralized fish manure (t = 41 d) with and without fertilizer amendment versus a conventional hydroponic fertilizer solution. Lettuce seedlings were grown in hydroponic grow boxes for 28 days. The fertilizer-amended treatments outperformed the treatments without additional fertilizer in terms of growth but had a lower nutrient use efficiency. The treatments growing in a nutrient solution based on manure from fish fed with a plant-based diet performed best, both in the fertilized and unfertilized treatment group. The results indicate a biostimulatory effect of the remineralized fish manure. Fish manure originating from freshwater fish such as O. niloticus that were fed diets with a high inclusion rate of plant-based feed ingredients such as pea or faba bean meal appears thus to be a promising feedstock for amended organic nutrient solutions that allows for fertilizer savings while increasing yield.