Fish are aquatic cold-blooded vertebrates with fins and scales. Many species of fish are often kept as pets in containers known as aquariums. Fish are generally divided into two groups: freshwater-dwelling and saltwater-dwelling, and fish from one group are generally unable to survive in the environment of the other. There are, however, a small number of species that move between saltwater and freshwater at different stages of their lives.
Types of fish
What the Bible says about fish
FISH. Creation of, Gen. 1:20-22. Appointed for food, Gen. 9:2,3. Clean and unclean, Lev. 11:9-12; Deut. 14:9,10. Taken with nets, Eccl. 9:12; Hab. 1:14-17; Matt. 4:21; Luke 5:2-6; John 21:6-8; hooks, Isa. 19:8; Amos 4:2; Matt. 17:27; spears, Job 41:7. Ponds for: in Heshbon, Song 7:4; in Egypt, Isa. 19:10. Traffic in, Neh. 13:16; John 21:13. Broiled, John 21:9-13; Luke 24:42. Miracles connected with: Jonah swallowed by, Jonah 1:17; 2; Matt. 12:40; of the loaves and fishes, Matt. 14:19; 15:36; Luke 5:6; 9:13-17; coin obtained from mouth of, Matt. 17:27; great draught of, Luke 5:4-7; John 21:6; furnished to the disciples by Jesus after his resurrection, Luke 24:42; John 21:9-13.
- "Which of you fathers, if your son asks for a fish, will give him a snake instead? Or if he asks for an egg, will give him a scorpion? If you then, though you are evil, know how to give good gifts to your children, how much more will your Father in heaven give the Holy Spirit to those who ask him!" Luke 11:11-13. 
Today there are over 10,000 species of fish, which is far more diversity that all other land vertebrates. This diversity pattern can be explain by the notion that fish, being aquatic, survived the <<Great Flood>>, while many land vertebrates went extinct during this catastrophic event