Buoyancy Characteristics of Non-Extruded BSF Maggot-Based Fish Feed Produced Via Rhizopus sp. Fermentation Using Cassava Residue

The metabolic activity of Rhizopus sp. during solid-state fermentation can alter the physical properties of feed substrates, particularly density and structural integrity, thereby enhancing buoyancy. Cassava residue (onggok), a byproduct of the tapioca industry rich in starch, may serve as an effective carbohydrate source to support fungal growth and improve pellet flotation without the use of extrusion. This study evaluated the effect of fermentation time and cassava residue addition on the buoyancy of black soldier fly (BSF) maggot-based fish feed fermented using Rhizopus sp. An experimental design was applied with three fermentation durations (36, 48, and 60 h) and a commercial sinking pellet as a negative control, each treatment conducted in five replications. Fermented pellets containing cassava residue were compared with pellets formulated without cassava. Buoyancy was assessed for up to 60 minutes of immersion in water. The results showed that pellets containing cassava residue exhibited significantly higher buoyancy, which increased with fermentation time. The highest buoyancy was observed at 60 h of fermentation, with 70% of pellets remaining afloat after 60 minutes, whereas pellets without cassava showed buoyancy below 20% at the same time point. These findings indicate that fermentation using Rhizopus sp. in combination with cassava residue has strong potential as an economical and environmentally friendly biological approach for producing floating fish feed without extrusion.