A land-owner digs a pond on his land. He does not stock the pond with fish. Yet, somehow, fish appear. Is this spontaneous generation?
The answer is no. Fish eggs are carried on the bodies of aquatic birds and other animals that move between bodies of water. Yahoo Answers says, “Think about the feathers on a duck (or any of dozens of different species of aquatic birds like geese, osprey, kingfishers, herons, loons, etc.). These birds spend most of their days swimming and diving in the murky shallows of lakes and ponds filled with fish eggs and frog eggs. Their feathers will be laced with eggs. If these birds then fly off and later take a dip in your pond (birds do like to preen themselves in clean water… which is why we build bird baths), you now have a pond seeded with frog or fish eggs. It can take a couple of years of many birds doing this before the fish take hold. But if there is enough food from the algae in the water, the fish with start to thrive.” If the new water-hole were indoors, covered, or in some way kept completely separated from animal life, fish would not appear.
Here is a point to ponder – think of God’s amazing creation. He created things in such a way that new bodies of water could soon be naturally stocked with fish and frogs. “O LORD, our Lord, How excellent is Your name in all the earth!” (Psalm 8:1, 9). “It is the glory of God to conceal a matter, but the glory of kings to search out a matter” (Proverbs 25:2). The more we study His creation, the more in awe we should be. “The heavens declare the glory of God; and the firmament shows His handiwork” (Psalm 19:1).