Question

why would there be selection for a fish to produce smaller eggs in colder water? what factors contribute?

Answer 1

The size of egg depends on largely environmental factors.Decline in oxygen levels in aquatic ecosystems leads to smaller sized eggs. Researchers proved that high flow environments produce larger sized eggs than expected. usually warmer fishes produces small eggs and colder region fishes produces large eggs.But due to pollution etc environmental damage oxygen levels decline and now a days fishes in cold water are in pressure producing small size eggs for their survival.(due to limited oxygen supply in aquatic ecosystems).