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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)