Moisture-induced pore restriction reveals a lower initial moisture window for aerobic composting of aquaculture-derived particulates.

Aerobic composting offers a sustainable route for recycling aquaculture-derived particulates, but appropriate moisture conditions for these fine and adhesive materials remain unclear because conventional criteria are mainly derived from terrestrial wastes. Aquaculture-derived particulates were composted for 28 d at initial moisture contents of 40%, 45%, and 50%. The 40% treatment maintained the highest porosity and more favorable oxygen conditions, entered the thermophilic phase (>50 °C) on day 8, and remained thermophilic for 13 d. In contrast, the 45% treatment sustained thermophilic conditions for only 6 d, whereas the 50% treatment never exceeded 50 °C and reached a minimum O₂ concentration of 5.3%. The 40% treatment achieved a 52.47% decrease in C/N ratio, a final germination index of 81.7 ± 6.3%, and an HA/FA ratio of 1.87 ± 0.06, indicating enhanced organic matter stabilization and humification. Higher moisture caused persistent oxygen limitation, prolonged NH₄⁺-N accumulation, ammonia loss, and increased greenhouse gas emissions. Microbial and metagenomic analysis were consistent with faster succession toward thermotolerant and aerobic degraders under 40% moisture, whereas higher moisture favored oxygen-limited metabolic potentials. Aquaculture-derived particulates also contained higher mucin-equivalent levels than the conventional substrates examined, suggesting that mucin may increase moisture-dependent adhesion and pore restriction. These findings demonstrate that aquaculture particulate-based composting requires a lower initial moisture level than commonly applied to conventional substrates, highlighting the importance of balancing water availability and pore aeration to improve compost stability and mitigate greenhouse gas emissions.