In the northeastern United States codfish are a big commercial business. Note the following facts: There is a market for eastern cod all over, especially in sections farthest removed from the northeast coastline. But the public demand posed a problem to the shippers. At first they froze the cod, then shipped them elsewhere, but the freeze took away much of the flavor. So they experimented with shipping them alive, in tanks of seawater, but that proved even worse. Not only was it more expensive, the cod still lost its flavor and, in addition, became soft and mushy. The texture was seriously affected.
Finally, some creative person solved the problem in a most innovative manner. The codfish were placed in the tank of water along with their natural enemy–the catfish. From the time the cod left the East Coast until it arrived at its westernmost destination, those ornery catfish chased the cod all over the tank. And, you guessed it, when the cod arrived at the market, they were as fresh as when they were first caught. There was no loss of flavor nor was the texture affected. If anything, it was better than before.
Each one of us is in a tank of particular and inescapable circumstances. It is painful enough to stay in the tank. But in addition to our situation, there are God-appointed “catfish” to bring sufficient tension that keeps us alive, alert, fresh and growing.
It's all part of God's project to shape our character so we will be more like his Son. Understand why the catfish are in your tank. Understand they are part of God's method of producing character in your life and mine.
–James S. Hewett, Illustrations Unlimited (Wheaton: Tyndale House Publishers, Inc, 1988) p. 14.