# Investigating the Effects of Fish Effluents as Organic Fertilisers on Basil (_Ocimum basilicum_)  
[PERSON]  
1 School of Design, University of Greenwich, Park Row, London SE10 9 LS, UK; b.  
livestock manure [6], and fish effluents (sludge or fish tank water) have been used successfully to fertilise various food crops, including tomato [7; 8; 9; 10; 11; 12; 13], pepper [14], chicory [15], lettuce [16; 17; 18; 19], cucumber [20], potato, soybean, and onion [21]. Up to 50% (in dry matter) of the feed consumed by fish is expelled as solids, forming sludge [22], and a significant portion of the nutrients introduced into an aquaculture system is wasted through the routine discharge of this nutrient-rich matter, which is primarily composed of fish excrement and unconsumed feed [23]. However, in most aquaculture farms, the sludge is released as sewage, and only occasionally is it dried and repurposed as fertiliser [24]. Aquaculture sludge holds considerable promise for enhancing plant growth due to its nutrient content [25], and a substantial amount of the essential macro- and micronutrients can be derived from this solid waste, which has been found to contain 7-32% of the total nitrogen and 30-84% of the total phosphorus present in wastewater [26]. The sludge is particularly abundant in phosphorus, a crucial macronutrient for plant growth which has been recognised as a Critical Raw Material in the EU due to its high supply risk, and conventional filtration in aquaponic systems eliminates over 80% of it [27]. The nutrient composition of filtered aquaculture effluents differs from that of sludge, with the latter offering a much richer and broader nutritional spectrum. Indeed, in comparison to sludge, filtered aquaculture effluent typically lacks phosphorus, potassium, calcium, and micronutrients, notably iron, molybdenum, and manganese [10]. Should the fish feed be organic in provenance, then the application of fish effluents could supply crops with organic fertiliser through a natural process observed in aquatic environments, where fish effluents contribute to plant growth in ponds and lakes [28]. Additionally, recycling wastewater that would otherwise pollute water bodies could offer a potential remedy for the environmental challenges associated with the eutrophication of aquatic ecosystems [29]. In this manner, the use of fish effluents could also fulfil an environmental conservation role by partially replacing the need for synthetic fertilisers, the production of which consumes significant energy [30], often sourced in environmentally damaging ways, such as phosphorus mining [31; 32]. In this study, the efficacy of two types of fish effluents (filtered and unfiltered) from an aquaponic system was tested to grow basil in greenhouse conditions. The main objectives were to test their viability as a source of fertiliser for the greenhouse cultivation of herbs, and to investigate their potential for maintaining and enhancing soil fertility and for enhancing the production of 'living soil', which are conditions that need to be fulfilled for organic certification in Europe. In order to ascertain the role of fish effluents in the growth of the plants as opposed to the nutrients already present in soil, the basil plants were grown in pots filled with two types of substrate, one compost-free and the other with compost. The filtered fish water is hereafter referred to as 'fish water', the unfiltered fish water as 'fish sludge' and the water from the tap as 'tap water'. When referring to both fish water and fish sludge, they are referred to as 'fish effluents'. A key novelty of this study is its direct comparison of compost and fish effluents as fertilisers for the cultivation of basil in greenhouse conditions.