Assertion (A) is true: Extrusion cooking in aquafeed manufacturing subjects the conditioned dough to high temperatures ($100^\circ\text{C}$ to $140^\circ\text{C}$) and severe mechanical shearing under high pressures ($30$ to $40\text{ bar}$) inside the extruder barrel. Reason (R) is true: When the hot pressurized melt exits through the die orifices into ambient atmospheric pressure, superheated water instantly flashes into steam, causing the starch matrix to expand rapidly and solidify with microcellular air pockets (expanded porous structure), allowing the feed pellets to float on the water surface. Thus, (R) explains why extrusion thermo-mechanical parameters are engineered to yield buoyant floating pellets.

Option analysis:

• Both (A) and (R) are true and (R) is the correct explanation of (A): Correct, steam expansion under pressure drop creates floating pellets.
• Both true but not explanation: Incorrect, (R) directly explains the rationale for using high temperature and pressure.
• is true but (R) is false: Incorrect, (R) is true.
• is false: Incorrect, (A) is true.