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Western Sand Darter

Range

Western Sand Darters primarily live in the Mississippi Basin,^[1] stretching from Minnesota to Louisiana. They tend to accumulate in Minnesota, Wisconsin, and Arkansas. In these areas, the populations tend to have at least 10,000 individuals. Western Sand Darters prefer to live in rivers with gravel or loose sand sediment and moderate to swift currents.

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  The general habitat of the Western Sand Darter.

Physical Description

Western Sand Darters are part of the Percidae family, which are slender fish that have translucent flesh. Their sizes can range from 1.7 to 2.6 inches. Clear flesh aids in making the fish look like the sandy bottom, a strategy used to evade predators. For some time, Western Sand Darters were grouped in the same category as Eastern Sand Darters.^[2] They stemmed from the Eastern Sand Darters by scale counts, opercula structures and pigmentation. The Western Sand Darter only has 3-5 scale rows, thin opercula spine, and are less colorful compared to the Eastern Sand Darter. Their scales are similar to placoid scales of cartilaginous fishes. Fish, such as sharks and rays, have hook like scales. Sand Darters have two dorsal fins that have spikes on them and a black stripe running from the anus to caudal fin.Caudal fins are the "tail" of most fishes. The type of caudal fin depends on the environment the fish lives in because its the main propeller of a fish's movement. Western darters have a truncate fin. It's squared off at the corners and used for shorts bursts of swimming. Because of their lifestyle, darters have a body shape called fusiform. This body, where the widest part of the fish is in the middle, produces as little drag as possible. These fish are swimming in fast currents have need to conserve energy while they're on the hunt. True spines are one of the characteristics of Perciformes. These spines are made out of bone, hence the name 'boney fish'. One of the more distinguishing features is the small sub terminal mouth. This occurs when the snout protrudes beyond the mouth.

Diet

Their diet mainly consists of larval aquatic insects such as Mayfly nymphs, midge larvae, and hyalella. When an animal mainly consumes insects, they’re called insectivores. Larvae don’t have many nutritional advantages so it takes many larvae to feed Western Sand Darters. The fish are able to hunt by the use of the lateral line system. This system senses changes in water pressure in their environment. If an insect were to be moving on top of the water, the fish would be able to find the insect. They counteract this by having low metabolic needs. They don’t have to maintain homeostasis like endotherms must but their osmoregulation still takes up 25% of their metabolic needs. Scientists have observed a unique behavior that the Western Sand Darter does to save energy in fast current systems. The fish will bury themselves into the sandy bottom to reach cooler temperatures ^[3]. Compared to the moving water, the sand is cooler. Fish metabolism slows in cooler temperatures and the fish can save energy.

Reproduction

The typical breeding season for these fish is between early July and August. Females tend to be larger compared to males. Because of their increased size, females produce an average of 57 eggs at a time. ^[4]. The eggs are then buried inside the river's sandy bottom. A study conducted by the University of Central Arkansas^[5] found that when females were of a smaller size they tend to have smaller egg clutches. The males don’t grow as large as the females because they aren’t needed for territory defense. The fish have greater reproductive success with larger females because they’re able to produce more offspring. The environment favors larger females because the average lifespan of the darter is three years. Because of their short life, darters grow up to 71% of their maximum size within their first year.

Conservation Status

Because not a lot of information is available on the Western Sand Darter the exact conservation status is unknown. But many agree that the population is vulnerable due to habitat destruction and fragmentation. The Mississippi River is one of the most polluted rivers in the United States and destroys the fishes’ environment. Nutrient run off and pesticides affect the nutrient concentration in rivers.^[6] When excess nitrogen and phosphorous, commonly found in fertilizer, accumulate in rivers it spurs excess plant growth. When the plants decay, the oxygen content decreases because oxygen is needed for decomposition. Pesticides are toxic to invertebrates and invertebrates severe as a food source for many fish. If the fish’s food supply depletes then the fish won’t have enough resources to reproduce. In Iowa, the populations seem to have been decimated from the Des Moines and Shellrock rivers.^[7] Impoundment is another way that the Darters are losing territory. Impoundment is the act of creating a water reservoir used for coal processing. In some areas, the population has remained stable but to the lack of information that could be skewed.

Etymology

The scientific name for the Western Sand Darter is Ammocrypta clara. “Ammoncrypta” means concealed in sand while “clara” means clear. The scientific name is indicative of the Darter’s tendency to bury itself in sand, while “clara” alludes to its translucent flesh.