This article collects recorded instances of three-eyed fish and asks the question: are they more common now, or are we just more likely to notice and publicize them?
In the television show The Simpsons a three-eyed fish dubbed Blinky derails Mr Burns' campaign to become Governor. Despite trying to put a positive spin on Blinky's extra assets Burn finds he cannot literally swallow him--Spitting out a mouthful of fish at a photo op at the Simpsons' house.
But surely there is nothing like Blinky actually in existence? After all, it stretches belief that nuclear outflow would really have such an obvious effect....
It is probably no coincidence that many rel three-eyed fish were reported in the years after the "Blinky" episode aired. While many would point to pollution and radiation as the reason, it is just as likely that the fictional three-eyed fish made people more likely to both notice and reporting finding this particular deformity--and the internet provides a way for them to thread and be permanently recorded. The following examples show that the three-eyed abnormality has been observed in many different species and locations.
Pike (2010): This video purports to show a three-eyed pike. And there are an apparent proliferation of cases of three-eyed fish over recent years.
Wolf Fish (2011): Fast forward to Argentina in 2011. Fishermen have caught a three-eyed wolf fish in a lake that received used coolant water from a nuclear power plant. No word yet as to whether any local millionaires are running for public office.
Bass (2013): A three-eyed fish was caught and released in a Missouri pond.
Pickering (2014): Another example popped up in a lake in Canada.
Mutant Fish as Sentinels
Despite my previous disclaimer, it is true that fish are often indicators of the presence of toxins in water supplies. they are essentially the aquatic version of the canary in the coal mine. For example a two-headed trout in Idaho (2012) was linked to selenium leaching into the water due to mining activities.
Many fish, amphibians and reptiles have a photosensitive area in their forehead called the "parietal eye". Third eyes may represent an atypical development of this region that is either spontaneous or prompted by some toxin or other mutagenic influence.
A Dr. E Gudger reported a number of three-eyed fishes from the 1920s including a haddock (1927) from Boston. This suggests that although accounts were harder to collect, the three-eyed abnormality has been occurring in fish for some time and there is no reliable way to tell whether it occurs at a higher rate now than in any other time in history. (Although the matter is complicated further by Gudger's later report that the infamous haddock was in fact a fake).
The 1910s, 20s, and 30s seemed to be another time where accounts of this kind were enthusiastically collected including a dab (1910), three-eyed salmon (1926) and another (apparently authentic) haddock from Canada (1935)--See Dawson (1965).
So the answer to my opening question about whether three-eye fish have become more common, or occur at the same rate and are just more commonly reported, is... there really is no way to know.
Dawson, C. E. (1964). A bibliography of anomalies of fishes. Gulf and Caribbean Research, 1(6), 308-399.
Gudger, E. W. (1928). A three-eyed haddock, with notes on other three-eyed fishes. The American Naturalist, 62(683), 559-570.
Gudger, E. W. (1930). IV.—The three-eyed haddock, Melanogrammus æglefinus, a “Fake.”. Journal of Natural History, 6(31), 44-48.