Microbiology, Biotechnology and Genetics: Principles and Interconnections Vol. 1

Fish-processing and aquaculture residues contain nitrogen, phosphorus, potassium, amino acids, peptides, minerals and organic carbon that can be recovered as fertilisers rather than discarded. Interest has expanded from simple nutrient recycling towards the possibility that fish-waste-derived inputs also act as plant biostimulants by altering root development, nutrient acquisition, photosynthesis, stress responses and rhizosphere processes. This critical narrative review evaluates evidence for such phytostimulatory effects across fish protein hydrolysates, fermented liquid fertilisers, fish emulsions and silages, fish-waste composts, and aquaculture effluents or sludge. Literature published from 2000 to 4 August 2026 was identified through agricultural, biomedical and multidisciplinary scholarly sources and critically appraised for product characterisation, controls, crop context, mechanism, scale and external validity. The strongest direct evidence concerns fish protein hydrolysates, for which controlled studies repeatedly report changes in root or shoot growth, chlorophyll status, gas exchange and stress tolerance. Field and greenhouse studies of fish-derived liquid manures and composts also demonstrate agronomic value, but these responses frequently reflect nutrient replacement and mineralisation rather than a separable biostimulant effect. Hydroponic studies provide an important counterpoint: fish-derived nutrient solutions can increase selected quality or physiological traits yet may underperform balanced inorganic nutrition when ammonium accumulation, nitrate limitation or incomplete mineralisation constrains growth. Across the literature, nutrient-matched controls, compositional standardisation, dose normalisation and multi-site field validation remain uncommon. Consequently, the central unresolved question is not whether fish waste can support crop production, but when and to what extent effects exceed those expected from its nutrient content alone. Progress requires experimentally separating nutritional and signalling mechanisms, defining peptide- and amino-acid-active fractions, resolving microbial mediation, and integrating agronomic efficacy with contaminant, salinity, pathogen and economic assessments. Fish-waste-derived fertilisers are therefore best viewed as a heterogeneous platform whose phytostimulatory potential is promising but formulation- and context-dependent.