# Investigating the Effects of Fish Effluents as Organic Fertilisers on Basil (_Ocimum basilicum_)
## 4 Discussion
For treatments IF, IFS and CFS, the species count was higher halfway through the experiment than at the end, the difference being the lowest (5 more species) for IF, higher for IFS (35 more species), and highest for CFS (255 more species). This could be due to some initial measured increase in diversity derived from the seedling substrate, which then stabilised and decreased. The initial compost substrate was higher in diversity than the initial compost-free substrate (139 more species, or a 20.47% increase), most likely because of the enhancing effect of composted green material. This initial higher diversity in the compost substrate likely resulted in a higher microbial diversity in the treatments with compost substrate (CT, CF, CFS) than in the treatments with compost-free substrate (IT, IF, IFS); indeed, as the nutrients already present in the substrate combined with the nutrients provided by the fish effluents, in the same way, the microbial diversity supplied by the compost was enhanced by the supplementation of fish effluents. It has been found that potting soil mixed with compost can indeed lead to higher microbial diversity. The authors of [55] highlighted that composting leads to changes in bacterial and fungal communities, indicating an increase in microbial diversity. [PERSON], [PERSON] et al. [56] reported that compost can effectively replace peat-based potting media without negatively affecting plant growth, indicating the potential for compost to enhance microbial diversity in potting mixes. These findings are consistent with the study by [57], which shows that compost-based growing media can improve soil microbial activity. The introduction of compost into potting mixes was shown to enhance microbial diversity, as evidenced by the changes in bacterial and fungal communities, thus supporting the findings of this study. _Massilia_, a major group of rhizosphere- and root-colonising bacteria [58], was present in the six most prevalent genera across all treatments. _Micromonospora_, a group of aerobic, mycelium-forming bacteria [59], was only present within the six most prevalent genera in the compost-free substrate treatments (IT, IF, and IFS), and _Lysobacter_ and _Devosia_ only in the treatments with compost substrate (CT, CF, and CFS). _Lysobacter_ has been observed on the surface of fish tanks of aquaponic systems [60], as well as in RAS biofiliter samples of aquaponic systems [61]; this genus has been identified as a plant growth-promoting bacterium (PGPB) that protects plants from disease through the production of antibiotics [62]. _Devosia_ contains some potential nitrogen-fixing bacteria, and the genus has been found to grow on lettuce (_Lactuca sativa_) roots in aquaponic systems [60], as well as in all biofilters and sums of an aquaponic system [61]. Taking only the most prevalent six genera into account per treatment, specific genera were only observed in treatments with compost substrate, and others only in treatments with compost-free substrate. This distinction is likely to have been caused by the initial substrate composition and the microbial communities associated with each. From the genera found, there does not seem to be a pattern associated with any specific treatment. In fact, in both bacterial and archaeal, and fungal analyses, most genera were found across multiple treatments. The impacts of fish effluents on the soil microbiome have not been extensively studied, especially not in greenhouse conditions. Some studies have however found that irrigation with fish effluents changes the structure of soil microbial communities. [PERSON], [PERSON] et al. [63] showed that aquaculture wastewater irrigation can change soil microbial functional diversity and community structure in arid regions, highlighting the potential impact of fish water irrigation on soil microbiota. [PERSON], [PERSON] et al. [64] found that the soil bacterial communities in rice fields irrigated with aquaculture wastewater can be impacted by the intestinal bacteria of the fish.