Reproduction and Age and Growth in Wisconsin Darters

Etheostoma microperca. Least Darter.
The spawning period in Wisconsin occurs from mid or late April to early July. In the Ann Arbor (Michigan)
region, spawning occurred from the middle of April to the fIrst or middle of June (Winn 1958b). In the Bell
Branch of the River Rouge, Michigan, spawning occurred on May 5 in 0.15 m of water, with temperatures ranging
from 13.5 0 C in the morning to 15.5 0 C in the afternoon (Petravicz 1936). The pH.of the water was 7.9-8.0. He
also noted a spawning on April 26 at a water temperature of 12 0 C. In the Gasconade River, Kansas, spawning
occ4ued on April 5 when water temperatures were 12.8 0 C (Cross 1967). .
fiJ:1f Wisconsin, one age I female collected in May had 146 ova 1 mm in diameter. Two age I females in June
had 150 and 194 mature ova.
In Wisconsin specimens, the ovaries were best developed during May (I9% of the body weight) and remained
high through July (12.92% of the body weight) (Figure 9). The ovaries in September comprised only
1.89% of the body weight. The testes were largest in June and July, comprising 1.21 and 2.78% of the body
weight. They dropped to 0.4% of the body weight by September.
Age and Growth:
A total of 254 specimens from Wisconsin were examined for age and growth. Of these, 243 came from central
Wisconsin and 1 I from the southern region (Table 7). The central Wisconsin fIsh grew slightly faster than
those from the southern region of the state (Figure 10). In central Wisconsin age 0 fIsh in September were 25-36
mm TL and in southern Wisconsin in August were 24-26 mm TL.
Age I fIsh in central Wisconsin were 35 (2841) mm TL. The mean calculated TL at the first annulus was
31. I 8 mm. In southern Wisconsin, age I fish were 32.5 (32-33) mm TL, and the mean calculated tL at the first
annulus was 29.75 mm. In Ohio, Trautman (1957) found adults ranging from 25-37 mm in length. The largest
specimen from Ohio was 45 mm in length.
Table 7. Age and growth of Least Darters in Wisconsin.
Central Wisconsin
Age Class No. ofFish Total Length in mm
Mean Range
I
II
38
1
Grand Ave.
Increments of
Growth
No. ofFish 39
35.00
38.00
(2841)
(38)
Southern Wisconsin
Mean Calculated Total Length(mm) at Annulus
1 2
3 I .21
30.00 38.00
31.18
3U8
39
38.00
Age Class No. ofFish Total Length in mm Mean Calculated Total Length (mm) at Annulus
Mean Range 1 2
6.82
1
2 32.50 (32-33) 29.00
II 2 35.00 (35) 30.50 35.00
. Grand Ave. 29.75 35.00
Increments of
Growth 29.75 5.25
No. of Fish 4 4 2
18
f"
,
i
I