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Fish form the main series of animals along the south side of the lower balcony. They have been around for about 500 million years, and over that immense time period many evolved specialised bodies and complex patterns of behaviour. The porcupine fish Diodon hystrix is one of a number of puffer fish, which can inflate their bodies to many times their normal size. This is a strategy to scare off would-be predators. If a predator did manage to sneak up on a puffer fish and swallow it, the result could be both painful and fatal.
The Amazon River is home to several species of fish known as piranha, including Serrasalmus rhombeus shown here. They form shoals and have been known to attack animals entering the river to drink, using their ferocious teeth to reduce their prey to a skeleton in minutes. Piranha are caught and eaten by the people of the Amazon Basin. If you have less dangerous prey in mind, you should consider fish such as the perch Perca fluviatilis, which is a popular target of anglers in Ireland. Here it has been introduced, as is also the case in countries as far away as Australia and New Zealand. Described as both sporting and palatable, perch are native in continental Europe. A German perch served as the original from which this modern plastic cast was made. This reproduction technique allows faithful attention to detail and true-to-life colours.
Fish may have reason to fear larger predators, but few would expect to be swallowed by an animal smaller than themselves. This specimen of the black swallower Chiasmodon niger has managed to fit a larger fish into its mouth. When it was found floating on the surface of the ocean near Dominica in the West Indies in 1865, a specimen of Scopelus macrolepidotus was visible in its extended stomach.
In addition to highly developed fish, there are primitive forms with ancient fossil relatives, such as the hagfishes, and ‘living fossils’, including the bowfin Amia calva illustrated here. These belong to fish groups that were abundant in the distant past but are represented today by only a few species – hence the name ‘living fossil’. The features of its ancient ancestors may still be seen in the bowfin. It can survive in almost stagnant, oxygen-poor water because it is able to extract oxygen by gulping at the surface, unlike most fish, which can breathe only by passing oxygen-rich water across their gills. Like many fish specimens, this bowfin is preserved as a painted plaster cast because its skin is too delicate and oily to be stuffed effectively.
The most famous ‘living fossil’ fish is the coelacanth Latimeria chalumnae, thought to have died out along with the dinosaurs until the first living example was discovered in 1938. Fish gave rise to the first vertebrates with limbs over 400 million years ago. The strong, bony fins of the coelacanth and its ancient relatives were ideally designed to evolve into limbs, thus providing an essential feature of land-based animals – the ability to walk. The oldest footprints in the world are to be found in rocks on Valentia Island, County Kerry, where tracks of a four-legged amphibian were discovered in 1992.