While the belief or disbelief in a talking fish may seem to be inconsequential, it raises some very serious problems. Today we may believe in a talking fish while tomorrow it may be a talking golden calf or a large golden image, sixty cubits high, that shouts out “I am god your god.” It was only Doniel who realized that this was simply impossible and reached into its throat and removed the cleverly concealed Name of G-d that it suddenly became mute.
For thousands of years evangelist priests have convinced the gullible that that their idol can cure the incurable and do the impossible. Millions of very gullible believers drink their holy waters and immerse themselves in their rivers in their belief that it will bring them salvation.
Most recently a person masquerading as a great kabalist scammed thousands of people of their hard earned money by claiming that he could cure them by correcting mistakes he supposedly found in their kesubah. Thousands of people fell for his clever scheme. When a bunch of quacks get on the air and claim that their deceased rebbi is still alive and is in fact the messiah, and even have a large following, it only proves how gullible people are. Over and over again people lose their money to pyramid or Ponzi schemes which promise them huge impossible returns on their money only on account of their great gullibility. That so many intelligent people fell for the fish story, hook, line and sinker, only goes to prove how gullible people are and how easily we accept even the supernatural and the bizarre.
The Torah warns us against the belief in superstitions. The Rambam in Hilchos Avoda Zarh, chapter 11, explains that such beliefs can lead to serious consequences and easily mislead people into serving idols.