Age, Growth, and Food Habits of the Fathead Minnow, Pimephales promelas, in North Dakota Saline Lakes

Fathead minnows (Pimephales promelas Rafinesque) were abundant in 9 of 10 prairie pothole lakes in south-central North Dakota, selected to represent extremes in salinity. Fathead minnows were found in lakes with mean concentrations of total dissolved solids during ice-free periods ranging from 385 to 7,036 mg/liter; no fish were found in North Lake George with a mean concentration of 23,489 mg/liter total dissolved solids. Crustaceans were the most important food group by number, volume, and frequency of occurrence in 541 fathead minnow intestines collected from seven lakes during summer and fall 1969. Of the Crustacea, cladocerans were most important, followed by copepods and amphipods. Analysis of 30 brook sticklebacks (Culaea inconstans) from Wildlife Lake, 13 Iowa darters (Etheostoma exile) from Barnes Lake, and 5 tiger salamander larvae (Ambystoma tigrinum) from South Alkaline Lake indicated that Crustacea was the most important food group for these organisms also. Fathead minnow fry appeared in early June and were seined (0.32-cm mesh) throughout the summer from 1 July to 1 September. The mean total length was 41 mm at the end of the first year of life and 58 mm at the end of the second. Only one fathead minnow from 2,100 aged had three annuli. Most fathead minnows in the lakes studied matured and spawned during their second summer and then died. The relationship between total length (TL) and weight (W) for 2,689 fathead minnows collected from nine lakes during the summer and fall of 1969 and 1970 was Log W = −5.7204 + 3.5178 log TL. The largest fathead captured was a 79-mm male weighing 6.7 g. Infestations of Ligula intestinalis ranged from 4.4 to 38.0% in five of eight lakes from which data were available. Host fathead minnows were characterized by reduced gonads. Severe winter conditions in this area frequently result in partial winterkills of fathead minnows that stimulate rapid growth of survivors by reducing the effects of density-dependent limiting factors.