Minnows (Family Cyprinidae)

Keith Farnand

The minnow family (Cyprinidae) is the largest family of fishes in North America and contains about 2100 species worldwide (Page & Burr, 1991). It is present on all continents except South America, Australia, and Antarctica with its greatest diversity in the South East Asia region. In North America we have about 230 of the 2100 species present in our waters.

The name minnow is often applied to mud minnows (family Umbridae), killifishes (Cyprinodontidae), and in general, many of the smaller juvenile fishes (Phillips, Smid, & Underhill, 1982). In order for a fish to be a true minnow, though, it must be of the family Cyprinidae.

Most minnows are usually small, but some, such as the introduced grass carp (Ctenopharyngodon idella) and some other species native to western North America grow to a size of 20-100lbs. The minnow is often thought to be any small fish, but in fact, they can grow to be as long as 3m and up to 100 lbs. The smallest of the minnow family matures at a length of 10mm.

The physical characteristics of minnows are sometimes easily confused with that of the sucker, since they are closely related, but they are different in many ways. Minnows lack the sucker-like mouth, but some minnows such as the longnose dace (Rhinichtys cataractae) do resemble the mouth of a sucker somewhat. Both suckers and minnows lack teeth in the mouth, instead both have pharyngeal teeth deep in the throat that grinds the food up against the basioccipital bone. Minnows, however, have more teeth than the suckers. The minnow may have up to three rows of teeth where the sucker would only have one row. Also, minnows do not have spines, except for some non-native species such as the carp (Cyprinus carpio) and goldfish (Carassius auratus) (Eddy & Underhill, 1969). Generally, minnows have 1 dorsal fin, and a pair of abdominal pelvic fins. The dorsal usually has less than 10 rays, but some of the introduced species may have more than 10. The members of the minnow family always posses a lateral line which is used for motion detection.

Minnows are very important fishes to the aquatic community as they serve as a food source for many of the larger predatory fishes, as well as birds. They are valuable to these larger fishes since they are easily found in large numbers and are usually quite small which makes them easy to catch. Also, minnows are of value to humans economically. For many years bluntnose (Pimephales notatus), fathead (Pimephales promelas), and shiner (Luxilus cornutus) minnows have been used as bait for both commercial and sportfishing. As a result the bait industry of North America has become quite large, and depends upon the abundance of minnows for growth. There are some minnows that are used for food such as the carp, but generally speaking they are not thought of as a food source due to their extensive ribs, and often "muddy" taste (Eddy & Underhill, 1969).

Minnows show a great deal of variation in their food sources. They can be either omnivores or carnivores. The omnivores tend to eat more herbaceous materials and thus have molar-like teeth that are used for grinding up the food. They also have specialized intestines that are longer and are black in color since the plant food takes longer to digest. The minnows that feed on minute animal lifeforms generally spend most of their time in the middle of the water column, since that is the most abundant source of food for them. These minnows have hooked teeth with or without serrations that are used to either pierce the skin, or shred the prey (Eddy & Underhill, 1969).

Minnows are able to occupy a wide variety of habitats as a result of their ability to feed on common plant/animal life in streams, lakes, and rivers. Also, as water temperature decreases in minnow environments, they become more and more nocturnal (Greenwood & Metcalfe, 1998). This study used the minnow Phoxinus phoxinus and showed that as water temperature decreased, minnow activity became more nocturnal, and their use of refuge decreased. This increased nocturnal activity was believed to be an adaptation of the minnows to avoid diurnal predators as the predators became less and less active as water temperature decreased, and as a result minnows were less likely to seek refuge.

Most minnows spawn in the spring or early summer, but there is some variability to this according to species. Some minnows, such as the carp tend to crowd themselves into shallow water where they will deposit their eggs and splash them around. Other species go through elaborate patterns for spawning. One example is when the male builds a nest made of stones where the female deposits her eggs, and the male fertilizes them. The male will usually then guard the nest from other fishes until the eggs are ready to hatch, at which point he leaves. As a result of the abundance of minnows in small areas, there is often cross-fertilization of the eggs and thus hybrids are created. These hybrids are very common, and are quite difficult to identify from the original species (Eddy & Underhill, 1969).

Although many small fishes are thought to be minnows many are not, they must belong to the Cyprinidae family in order to be a minnow. The minnow is a family of fishes that is able to survive in a wide variety of climates, and habitats as you can see due to its geographic dispersion. The minnow is not only important to the aquatic food chain for predation and food, but also to humans for use in the bait industry.

REFERENCES

"minnow" Encyclopedia Britannica Online. available. http://www.eb.com:180/bol/topic?eu=54192&sctn=1 . October 19, 1999.

Greenwood, M. & N. Metcalfe. 1998. Minnows become nocturnal at low temperatures. Journ. of Fish Biol. 53: 25-32.

Page, L. & B. Burr. 1991. Freshwater Fishes. Houghton Mifflin Company. New York, New York. 63 p.

Eddy, S. & J. Underhill. 1969. How to know the freshwater fishes. Wm. C. Brown Company. Dubuque, Iowa. 60 p.

Philips, Schmid, & J. Underhill. 1982. Fishes of the Minnesota Region. University of Minnesota Press. Minneapolis, Minnesota. 108 p.