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FISH HAVE SCALES Most fi sh have scales that cover their bodies and overlap each other like shingles on a roof. Just like a roof protects a house, scales protect a fi sh. Scales are typically composed of calcium carbonate and collagen and are strong, yet fl exible. They can increase in size as a fi sh grows, but they don't increase in number; however, damaged and missing scales can be regrown. Some fi sh, like trout, have very small scales; others, like common carp, have large, thumbnail-sized scales. Fisheries managers can often determine the age of a fi sh by looking at its scales. As scales grow, rings are created similar to rings of a tree. In temperate climates, the spacing between the rings becomes constricted during the winter when growth is minimal. The number of years a fi sh has lived can be counted by the number of constrictions in the growth rings. PHOTO BY LINSEY CHIZINSKI Third Winter Second Winter First Winter Center d C PADDLEFISH – A UNIQUE FISH IN NEBRASKA The American paddlefi sh (Polyodon spathula) is referred to as a "primitive fi sh" with few changes in the fossil record to the Late Cretaceous period, seventy fi ve million years ago. It is one of only two species in the paddlefi sh family and exists only in the Missouri and Mississippi River systems; the other exists as critically endangered in the Yangtze River of China. Many of the paddlefi sh's characteristics are unique from other Nebraska fi sh species. Particularly different is its cartilaginous skeleton and tail shape, similar to sharks. The paddlefi sh is most notable for its paddle-shaped rostrum, which is covered with sensory pores and believed to be used for detection of its food source of zooplankton. It collects zooplankton by fi lter feeding as it swims with its mouth wide-open. The passing water is sieved by specially adapted gills that collect and moved the trapped organisms to the intestinal tract. Since paddlefi sh do not actively feed on lures or baits, they are caught by a snagging and archery methods during special seasons on the Missouri River. See the current Fishing Guide for details. The Nebraska state record paddlefi sh is 107 pounds, 12 ounces. PHOTO BY JULIE GEISER C. IVERSON, MINNESOTA DEPARTMENT OF NATURAL RESOURCES 34 34 34 34 34 34 34 34 34 34 34 34 34 34 34 34 34 34 34 34 34 34 34 34 34 34 34 34 34 34 34 CHAPTER 6 ● FISH ANATOMY