A shadow zone in the river is:

Correct option is C

Correct Answer: (c) Unsuitable spawn collection ground
Explanation:
→ A shadow zone in a river refers to areas with weak currents and stagnant water.
→ Such regions do not allow proper drifting of fish spawn and thus are unsuitable for collection.
→ Ideal spawn collection requires moderate flow for natural drifting of eggs.
Information Booster:
→ Shadow zones often accumulate debris and predators, further reducing spawn survival.
Additional Information (Other Options):
(a) & (b): Productive zones require clean flow, not stagnant water.
(d) River mouths: High nutrient mixing zones, not shadow zones.