Though mermaids and mermen are usually found in fantasies and fairy tales, they make a fair number of appearances in science fiction too. Peggy Kolm compiles a great list of undersea humans from SF books.
The intriguing post from The Reef Tank blog, called "Mer-Women and Fish Men: Humans Engineered for Ocean Living," begins in the '50s with James Blish:
In James Blish's 1952 classic short story "Surface Tension" humans crash land on a water covered planet. As their supplies are running out they create a race of microscopic aquatic humanoids to carry on their legacy. The small creatures eventually develop technology advanced enough to escape the bounds of their environment, breaking through the surface tension of their watery world in an "air ship".
The survey also looks at work by Vonda McIntyre and other writers, and offers this delicious excerpt from British sf writer Alastair Reynolds:
Vargovic had seen pictures of mermaids in books when he was a child; what he was looking at now were macabre corruptions of those innocent illustrations. These things were the same fusions of human and fish as in those pictures - but every detail had been twisted toward ugliness, and the true horror of it was that the fusion was total; it was not simply that a human torso had been grafted to a fish's tail, but that the splice had been made - it was obvious - at the genetic level, so that in every aspect of the creature there was something simultaneously and grotesquely piscine. The face was the worst; bisected by a lipless down-curved slit of a mouth, almost sharklike. There was no nose, not even a pair of nostrils; just an acreage of flat, sallow fish-flesh. The eyes were forward facing; all expression compacted into their dark depth.
via <a href="">The Reef Tank
Post author, Peggy Kolm, runs the Biology in Science Fiction blog.
Image via Atomic Bear Press