Becker, George C. / Fishes of Wisconsin
Minnow and carp family - cyprinidae, pp. 415-605 ff. PDF (93.4 MB)
598 Minnow and Carp Family-Cyprinidae The bluntnose minnow in Pewaukee Lake (Wau- kesha County) grows rapidly, attaining a calculated total length of 51.3 mm at the first annulus. The age composition of a 9 September collection was: 0--43.5 (38-49) mm; 1-61.3 (54-67) mm; and 11-82.2 (77- 85) mm. In a 27 September collection from the west- ern end of Lake Mendota (Dane County) (D. Schmitt, pers. comm.), the calculated total length at the first annulus was 43.3 mm, and the age composition was: 0-43.1 (24-57) mm; 1-60.9 (55-66) mm; and II- 75.1 (71-80) mm. In a 16 September collection from the Plover River (Portage County), the calculated to- tal lengths at the first and second annuli were 39.5 and 60.9 mm respectively, and the age composition was: 1-52.5 (50-55) mm; 11-64.0 (58-70) mm; and 111-86.7 (81-92) mm. The annulus for the year was just being deposited for the largest and oldest fish in these collections. Females reach maturity at age I, and males at age II (Westman 1938). Females may pass through at least two spawning seasons, and possibly a third. Males reach a length of 102 mm (4 in), and females, 76 mm (3 in) (Dobie et al. 1956). The maximum known total length reported is 108 mm (4.3 in) (Traut- man 1957). The bluntnose minnow is primarily a bottom feeder, supplementing its diet with surface insects and plankton (Moyle 1973). Keast (1965) classified this species as a specialized feeder, since the bulk of the diet is made up of three items. Food consists chiefly of small organisms taken from the bottom, from water plants, and from the water. The literature includes a number of reports in which diatoms and filamentous algae constitute a substantial part of its diet. In Minnesota during the winter, Moyle found the gut of this minnow packed with 90% large dia- toms and 10% filamentous algae; he suggested that algae probably make up most of the winter diet of this species. In August and September, the bluntnose minnow in Green Lake (Green Lake County) consumed insect larvae (50%) and insect pupae (50%); in Lake Men- dota (Dane County), it consumed adult insects (25.6%), cladocerans (31.4%), copepods (14.1%), plants (14.3%), algae (10%), and bottom ooze (4.3%) (Pearse 1921a). It is also known to eat fish eggs, fish fry oli- gochaetes, debris, silt, and even its own young (Do- bie et al. 1956). Hankinson (1908) saw individuals feeding on the eggs of black bass, johnny darters, sculpins, and sunfish of three species. In Long Lake (Minnesota), Moyle (1973) observed that in the early morning bluntnose minnows feed heavily on emerging chironomids. Apparently these fish move out of their normal habitat among the aquatic plants and into shallow areas at each end of the lake, where there are swarms of chironomids. Scuba observations indicate that bluntnose minnows are not active at night, but rest quietly on the bottom in open areas. In Lake Mendota (Dane County) during the winter the bluntnose minnow is found on the bottom at depths of 11-18 m (35-60 ft) (Black 1945b). When the ice cover has gone, the bluntnose enters the shoal areas. It occasionally leaves the shore regions if tem- peratures, wind, or other factors, such as the pres- ence of enemies, produce unfavorable conditions. Hankinson (1908) noted that the bluntnose is much less common in shallow water during the summer than in the spring. He also noted that in Walnut Lake (Michigan) it is most common over gravel bottoms and near submerged plants, rather than where the bottom is marly. In Long Lake (Minnesota), Moyle (1973) noted two seemingly contradictory tendencies in the bluntnose minnow's habitat preference: (1) a tendency to asso- ciate with larger schools of mimic shiners in water less than 1 m deep, and (2) a tendency to stay in small schools in water 2-4 m deep, among aquatic plants. Moyle observed an interesting relationship with the mimic shiners, in which the bluntnose min- nows in independent schools of 10-15 fish swam im- mediately behind and slightly beneath the large schools of mimic shiners. He presumed that the bluntnose were attracted by the protection and feed- ing advantages that a large school of fish could afford. Among aquatic plants, bluntnose minnows were usually found in independent schools of 10- 20 fish, which sought out the silty-bottomed open- ings that were scattered among the beds of aquatic plants. That the bluntnose minnow has a keen sense of smell, and can discriminate between the odors of aquatic plants, suggests that in nature it can separate odors as it swims about, much as a dog follows a trail amid a distracting host of odors (Walker and Hasler 1949). These authors imply that odor discrimination may guide fish to feeding grounds, and may prevent immature fish from straying from cover. The original work done by Hasler and others with the bluntnose minnow suggested that other natural odors may be responsible for directing migratory fishes (such as salmon) to locate their own homing areas. At an acclimation temperature of 25°C (77°F), the bluntnose minnow has an upper tolerance limit of 33°C (91.4°F); at an acclimation temperature of 15'C (59°F), it has a lower tolerance limit of VC (33.8°F)
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