With a lineage dating back before the time of the dinosaurs, fish are one of the Earth’s oldest and most enduring life forms. Scientists estimate that there are over 28,000 different species of fish on the planet, with huge variations in size and appearance among them. However, all fish – from the largest wild species that trolls the depths of the ocean to the tiniest goldfish happily swimming around its bowl – share many things in common, many of which you may not know about. Here are some lesser-known but fascinating facts about our scaly waterborne friends:
• Fish sleep with their eyes open. While relatively few species of fish have eyelids, the vast majority of them have only protective membranes that keep salt and debris from affecting their vision. Thus, in most species, the only clue that a fish is asleep is a decline in fin movement.
• Fish drink in order to breathe. Sure, we all know that fish use their gills to remove oxygen from water, but did you know that the mechanism by which they respire actually starts with drinking? After fish take a drink, they force the water out through their gills, which are equipped with a mechanism for extracting oxygen and delivering it to the fish’s bloodstream.
• Not all fish are confined to the water. One particularly amazing – and extreme – example of this fact is the climbing perch, a species of fish native to the Indian subcontinent. Given the aridness of India’s climate, bodies of water often dry up. The climbing perch has adapted to the extremes of its habitat by developing the ability to walk on land to search for another body of water to swim in.
• Like trees, fish accumulate rings that can be used to determine age. Ring-like structures grow both on fish scales and on bones in the fish’s inner ear. These rings indicate the seasonal and environmental changes the fish has lived through; they accumulate more quickly in summer and slow down in winter. In most fish species, close sets of rings indicate one summer, with a distant ring indicating one winter. By counting the number of summers and winters a fish has lived through, its age can be accurately determined.
• Most fish cannot swim backwards. Given the physical structure of fins, it is possible for the vast majority of fish species to propel themselves through water only in a forward direction. Some members of the eel family have the ability to swim backwards, but this ability is rarely if ever used in the wild.
• It’s believed that fish do not feel pain. While this point is currently under scientific contention from a minority of researchers, the general consensus is that fish do not experience pain the way most mammals do. For example, a fish caught with a hook will attempt to escape because of the unnatural introduction of a foreign object to its body, not because the hook actually hurts – most fish lack the frontal brain lobes that control pain sensations in most living creatures.
• Fish continue to grow throughout their lives. Unlike many other species, fish do not stop growing when they reach a certain age; however, the rate at which they grow does slow down as they get older.
• Most domesticated fish die because of sub-prime living conditions. It’s estimated that some 95 percent of pet fish fatalities are caused by contaminated water, incorrect water temperature or insufficient oxygen levels. Do your pet fish a favor – learn the fine points of aquarium care and ensure that your fish has a healthy environment in which to live at all times.
