Ethoxyquin (6-ethoxy-1,2-dihydro-2,2,4-trimethylquinoline) and BHT (Butylated Hydroxytoluene) are synthetic lipid-soluble antioxidants widely incorporated into fish diets to inhibit auto-oxidation and free-radical rancidity of marine oils and highly unsaturated fatty acids (HUFA) during storage.

A Demand Feeder (or pendulum feeder) is an in-pond automated feeding device consisting of an inverted hopper with a suspended pendulum rod extending into the water. When hungry fish touch or nudge the rod, a small portion of feed pellets is dispensed on demand, minimizing feed wastage and labor.

Feed utilization indices in fish nutrition:

• Food Conversion Efficiency (FCE) is defined strictly as the wet weight gain of fish produced divided by the total dry weight of feed fed: $\text{FCE} = \frac{\text{Weight Gain}}{\text{Feed Fed}}$ (often expressed as a percentage).
• Food Conversion Ratio (FCR) is the reciprocal of FCE, defined as the weight of feed fed divided by the weight gain of fish produced: $\text{FCR} = \frac{\text{Feed Fed}}{\text{Weight Gain}}$.
• Protein Efficiency Ratio (PER) is the weight gain of fish divided by the total crude protein intake: $\text{PER} = \frac{\text{Weight Gain}}{\text{Protein Fed}}$.
• Specific Growth Rate (SGR) is the percentage daily increase in body weight calculated logarithmically: $\text{SGR (\% day}^{-1}) = \frac{\ln(W_2) - \ln(W_1)}{t} \times 100$.
  Note: In the official NTA final answer key, marks were awarded for all options (1, 2, 3, 4). By definition, option 1 (Food conversion efficiency) is scientifically exact.