Extrusion technology in aquafeed manufacturing:
Assertion (A) is true: Extrusion processing subjects the feed mash to High-Temperature Short-Time (HTST) conditions (110-150 °C), elevated moisture (20-30%), and high pressure inside the extruder barrel.
Reason (R) is true: When the hot, pressurized plasticized dough is suddenly forced through the exit die into atmospheric pressure, superheated water instantly flashes into steam, expanding the starch matrix and leaving microscopic trapped air vacuoles inside the structure, which lowers the pellet density below that of water ($\lt 1.0\text{ g/cm}^3$) and enables the pellets to float.
Furthermore, the high temperature, moisture, and pressure described in (A) directly cause the steam flash and internal air-pocket formation described in (R).

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.

Matching aquaculture feed ingredients with their technological functions:

• Groundnut cake (GNC): Rich plant protein source containing $40\%$ to $45\%$ crude protein -> (A) matches (II).
• Tapioca flour: Gelatinized starch used as a pellet binder to enhance water stability -> (B) matches (I).
• Ethoxyquin: Synthetic antioxidant added to prevent lipid autoxidation in fish feeds -> (C) matches (IV).
• Rice bran: Energy-yielding carbohydrate source containing $45\%$ to $50\%$ digestible carbohydrates -> (D) matches (III).

In dry aquafeed storage, moulds (filamentous fungi such as Aspergillus flavus, Penicillium, and Fusarium species) represent the most frequent and economically devastating cause of spoilage. Whenever moisture content exceeds $10\%$ to $12\%$ in humid warehouses, fungal hyphae proliferate, degrading nutrients and synthesizing lethal mycotoxins (notably aflatoxin B1), causing severe hepatoma and mortality in farmed fish.

Option analysis:

• Bacteria: Require high water activity ($a_w \gt 0.90$), whereas dry feed has low moisture.
• Viruses: Obligate intracellular parasites, cannot grow or cause feed spoilage.
• Worms: Parasitic animals, not feed rot agents.
• Moulds: Correct, xerophilic and xerotolerant fungi that thrive on stored grains and feeds.