Question

What is the preferred fish food organisms for spawn of Indian major carps?

• A. Ostracode
• B. Rotifers
• C. Cladocerans
• D. Isopods

Hint:

Remember the progression of live feed preference as fish larvae grow: Rotifers (smallest, preferred by spawn) \( \rightarrow \) Cladocerans (larger, preferred by fry) \( \rightarrow \) Copepods.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
The spawn of Indian Major Carps (IMC), such as Catla, Rohu, and Mrigal, have undeveloped digestive systems and small mouths when they first begin feeding.
At this early stage, their mouths are physically too small to ingest larger zooplankton.
Therefore, successful rearing of spawn depends on providing tiny, highly digestible zooplankton of the appropriate size.

Step 2: Detailed Explanation:
When IMC spawn transition from utilizing their yolk sac to active feeding, they require live food that is both small enough to ingest and high in nutritional value.
Rotifers (such as Brachionus species) are the ideal first food for this stage.
They typically range in size from 100 to 300 micrometers, which fits the mouth gap of newborn spawn.
Rotifers also swim slowly, making them easy for the young fish to catch, and contain essential amino acids and enzymes that assist in digestion.
As the spawn grow and transition into fry, their mouth gap increases.
At this point, they can begin feeding on larger zooplankton such as cladocerans (e.g., Daphnia and Moina) and copepods.
Ostracods are generally avoided by early larvae due to their hard calcareous shells, while isopods are too large and structurally unsuitable.
Therefore, rotifers are the preferred and most important food organism for the first few days of IMC spawn rearing.

Step 3: Final Answer:
Rotifers are the preferred live feed for IMC spawn due to their small size and high digestibility.
Thus, the correct choice is (B).