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