His hair was long and dark, and it flowed out in the water around Him as He swam. Suddenly many fishes appeared and each fish took one strand of Baha'u'llah's hair in its mouth and followed Baha'u'llah as He kept swimming. 
The fish did not hurt Him, or slow Him down. When Bahil'u'llah turned one way, so did every fish. When He turned the other way, the fish followed that way. 
The fishes were following Baha'u'llah's light - the light of God in His heart. 
Baha'u'llah's father asked a wise man what his dream meant, and the wise man said that the ocean was like the world, and the fishes were the people. All the people would be attracted to the light of God in Baha'u'llah and would follow Him. They would attach their hearts to Him like the fishes in the dream attached themselves to His hair. The people would follow Baha'u'llah wherever He led them. 
Now we know that this wise man was talking about the Baha'is. We are the people who follow Baha'u'llah. Every day more people in the world find Baha'u'llah and follow Him. 
We can be like the fishes by following Baha'u'llah. If we do what Baha'u'llah teaches us, we will be full of God's light which He reflected on us.