The reproductive biology of the northern madtom, Noturus stigmosus Taylor, was examined in the Licking River, Bath and Rowan counties, Kentucky from 2001–2006. Gonadosomatic indices suggest a discrete spawning event in mid-summer, with sexual maturity reached at approximately 60 mm standard length (SL). Clutch size was estimated at 70–110 eggs per female based on examination of mature ovaries. Males and females come into reproductive condition in early summer and exhibit secondary sexual dimorphism typical of madtoms. Four nests were discovered in early to mid-July in water 23–25°C. All nests were in cavities under large slabrocks in a raceway with moderate current (0.36–0.69 m sec−2) above a large riffle. Nests contained 40–87 eggs or embryos; no guardian males were found with any nest. Eggs reared in the lab at 21–22°C hatched about 13 days after fertilization, which is the longest reported for madtoms. Embryonic and larval development were similar to those of other madtoms. Hatchlings were 8.1–9.3 mm total length (TL). By 10 days, the yolk sacs were absorbed, and young (now 15.4–15.7 mm TL) had acquired pigmentation diagnostic for the species. Approximately one month after hatching (at ∼20 mm SL), young moved downstream from the raceway into a large riffle.
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Vol. 69 • No. 2