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Identified as gasterosteiformes, the stickleback fish has three suborders which include the sticklebacks or Gasterosteoidei which includes the families Inodstomidae, sticklebacks or Gasterosteidae and the tube snouts or Aulorhynchidae, the trumpet fish or Aulostomoidei and seahorses grouped with the pipe fish which are also known as the Syngnathoidei. From the Indostomidae there is only one species that is known. The name of this species, Indostomus paradoxus, makes reference to a peculiar array of characteristics which are present in the species. While the individual row of spines in front of the dorsal fin is the main characteristic that shows this fish is related to the sticklebacks, the tube like head is elongated and the bony external skeleton is much more indicative of the pipe fish or seahorse group. Very little is known about the anatomy and habits of the Indostomus making a correct classification difficult until a more thorough study of this fish has been done.
Sticklebacks make up five genera, most of which have just one species. They live exclusively in the cold and temperate zones of the northern hemisphere with at least two genera living in the ocean and two genera living in fresh water while at least one genera is known to live in brackish water. These fish do not have scales, but instead have numerous vertical narrow bony plates that develope in the dermis. Under a microscope a fine network of lamellae is revealed. In front of the dorsal fin there is a number of free standing moveable spines that vary in number with each species. The diet of the stickleback fish consist mostly of insect larvae, worms, fish eggs, small crustaceans and young fish. Their spawning season begins around April and ends in June with the fish carrying their young. Many times there are several broods produced one after another with their life expectancy in the wild being around one to three years.
The three spined stickleback is the best known member of this family. It is known to live in freshwater, salt water and brackish water with the only continuous center of it's distribution for the species being along the coastlines. Sticklebacks that are found in fresh water are believed to be there due to an earlier migration from the ocean. Unlike others of their kind, freshwater sticklebacks tend to have very little armor while those found in the ocean have a substantial covering of the bony armor plate. In some cases there are sticklebacks that are transitional forms in terms of the armor covering. All three of these forms are found in the North Sea. These fish are migratory, moving into fresh water to spawn during the spring. When the spring thunder storms occur huge masses of sticklebacks can be seen gathering in the mouth of low land rivers to begin a massive upstream migration. This is especially prevalent in Germany. During this time the temperatures are higher and the day light hours increase causing the germ cells to accelerate in development toward maturity. Sexual maturity is reached during the upstream migration for both male and female sticklebacks. The females retain their coloration while the males take on a bright display of color with the throat and breast taking on a cherry red hue and the back acquiring a bright blue or deep green coloration. When the migration site is reached spawning takes place in sandy ground in shallow waters.
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