Early spawn of Indian Major Carps (upon yolk sac absorption at day 3, measuring only $5$ to $6\text{ mm}$ in total length) have an extremely small mouth gape ($100$ to $150\text{ }\mu\text{m}$). Consequently, tiny planktonic rotifers (such as Brachionus calyciflorus, Brachionus plicatilis, and Keratella, measuring $50$ to $200\text{ }\mu\text{m}$) are the preferred initial live food organisms. Larger cladocerans (Daphnia, Moina) are consumed only after the fry grow larger.

Option analysis:

• Ostracods: Hard bivalved carapaces, undigestible and too large for tiny carp spawn.
• Rotifers: Correct, ideal microscopic soft-bodied live food perfectly matched to spawn mouth gape.
• Cladocerans: Food for advanced fry and fingerlings, too large for newly hatched spawn.
• Isopods: Large benthic crustaceans, completely unsuited for carp spawn.

Mahua oil cake (derived from the seeds of Madhuca indica / Bassia latifolia) contains $4\%$ to $6\%$ of the hemolytic plant saponin mowrin. Applied at a dose of $2000$ to $2500\text{ kg/ha-m}$, it acts as an effective botanical piscicide by hemolyzing red blood cells and asphyxiating predatory and weed fishes within hours. Its toxicity dissipates within $10$ to $15\text{ days}$, after which it acts as an excellent organic fertilizer.

Option analysis:

• Mahua oil cake: Correct, traditional dual-purpose botanical piscicide and organic manure.
• Kerosene: Used as a thin surface emulsion ($50\text{ L/ha}$) to control aquatic insects, not fish.
• Diesel: Used in insecticidal emulsions, not for fish eradication.
• Cotton seed cake: Standard livestock and fish feed ingredient without piscicidal saponins.

Statement (I) is correct: Organic fertilizers (such as cow dung or poultry manure) supply particulate organic matter that fuels the heterotrophic/saprophytic pathway (decomposer bacteria and protozoa feeding on detritus), which in turn serves as food for zooplankton. Statement (II) is incorrect: Inorganic fertilizers (NPK) provide dissolved mineral salts that stimulate photosynthetic phytoplankton (autotrophic primary producers); zooplankton then feed on these algae via the autotrophic/grazing food chain, NOT through a saprophytic food chain.

Option analysis:

• Both correct: Incorrect because Statement II is false.
• Both incorrect: Incorrect because Statement I is true.
• Statement (I) is correct but Statement (II) is incorrect: Correct assessment.
• Statement (I) is incorrect: Incorrect because Statement I is true.