Size

• The fathead minnow will have a maximum length in the range of 3 to 4 inches, with the males larger than the females. One way to identify this species of minnow is to examine the anal fin, the fin on the underside of the minnow located before the tail. This fin will possess seven rays, the structures that support the membranes of fish fins.
  
  

Colors

• Olive-brown is the best way to describe the color of the back of a fathead minnow, with the mature specimens having a purple or copper tint in this region, states the Pennsylvania Fish and Boat Commission website. The fish's sides have a cream color, and females and males not engaged in breeding activity possess a stripe on the sides that is hard to detect near the head but is wider near the tail. The dorsal (top) fin on a fathead minnow has a small dark patch on the front margin.
  
  

Breeding Males

• The breeding male fathead minnow has a different look to it, with its head having two separate rows of bumps that resemble horns, called tubercles. These bumps are also present on each side of the fish's lower jaw. The color of the male's head turns black when it is in the process of breeding, with a copper-green color on the cheeks. A ring of copper surrounds the body behind the gills, with another such ring behind the dorsal fin. The entire body takes on a darkened tone.
  
  

Shape

• The body of the fathead minnow is chubby, making the fish take on a stout look. The fish takes its name from its head being big in proportion to the rest of the body. This minnow has a blunt nose. The top of its head is flat and the mouth is terminal, a biological term that means that it faces straight forward as opposed to being on the bottom or top of the face.
  
  

Considerations

• You may also identify a fathead minnow by where you find it. These fish are quite hardy and can exist in muddied, cloudy water that other species cannot inhabit. Waters with poor levels of oxygen will support the fathead minnow, as will places where the pH levels fluctuate from high to low. Populations of fathead minnows will live in locations such as bog ponds, the backwaters of streams where the bottom is muddy and small lakes.