Notropis nubilus (Forbes, 1878)
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Basis for Listing
Occurrences of the Ozark Minnow (Notropis nubilus) in Minnesota are restricted to the Zumbro, Root, and Cedar rivers, and their tributaries in southeastern Minnesota. These populations are isolated from one another and from other populations in Wisconsin and Iowa by virtue of unsuitable intervening habitat. Given the low likelihood of recolonization if any of these populations were decimated, the Ozark Minnow was listed as a special concern species in Minnesota in 1996.
The Ozark Minnow is a medium-sized slender minnow with an almost round body. Its body is silvery brownish-black above fading to silvery bronze below with a silvery-white belly. It has a prominent black lateral stripe that extends from its tail to the tip of its snout. The average total length of Ozark Minnow is 6.8-9.2 cm (2.7-3.6 in.) (Becker 1983). Breeding males and females exhibit an orangish-yellow pigmentation on their fins and lower half of the body. This coloration is more pronounced in males, who also develop pronounced tubercles (small, hardened, breeding growths) on their head and occasionally the pectoral fin (Hatch et al. in preparation).
The Ozark Minnow is very similar in appearance to the Pugnose Shiner (N. anogenus), Blackchin Shiner (N. heterodon), Blacknose Shiner (N. heterolepis), Weed Shiner (N. texanus), Pallid Shiner (Hybopsis amnis), and Pugnose Minnow (Opsopoeodus emiliae) (Lyons et al. 2012). Ozark Minnows can be distinguished from the rest by a long strongly coiled intestine that is twice an individual’s total length. The peritoneum is black, which is a characteristic shared only with the Pugnose Shiner whose peritoneum may be either black or brown. However, in Minnesota, the two species do not overlap in distribution.
The Ozark Minnow is found in clear small- to medium-sized streams of permanent flow, usually in areas of slow current near gravel and pebble riffles. It is common in waters of some of the least disturbed habitats in the state; those not subject to siltation, pollution, and the effects of cultivation (Hatch et al. in preparation).
Biology / Life History
The Ozark Minnow begins spawning in May and continues through July and perhaps into August. Its diet includes green algae, blue-green algae, diatoms, and occasionally small insect larvae and crustaceans (Becker 1983). The species schools near the bottom in shallow water, less than 30 cm (12 in.) deep. Both males and females reach sexual maturity at age-2 which is also their average life span.
Conservation / Management
Although populations of Ozark Minnows in the Zumbro and Cedar river drainages appear to be stable, their isolation from each other and other populations makes them vulnerable to catastrophic events, after which recolonization is unlikely. The species is also intolerant of excessive turbidity and siltation that may occur from heavy agricultural practices. The status of the Ozark Minnow population in the Root River drainage is unknown. Additional research needs for the Ozark Minnow include Minnesota life history studies and identification of habitat guilds.
Conservation Efforts in Minnesota
Minnesota DNR surveys have recorded Ozark Minnows 11 times since 1990. Berendzen (2008) received a grant in 2006 to study the genetic variation of populations of this species in Minnesota (Berendzen et al. 2008). Results of the study revealed a genetic distinction between Ozark Minnows in drainages east versus west of the Mississippi River, suggesting that the Mississippi River is a barrier to gene flow. In order to maintain the genetic diversity within the species, all Ozark Minnow populations in the state should be treated as a single genetic unit, and conservation efforts should include all drainages in the species range, namely the Zumbro, Root, and Cedar rivers.
The recent inception of Minnesota’s Clean Water Legacy Program will eventually yield benefits to Ozark Minnow habitats through nutrient and sediment load reductions.