Abstract:
Population structure, habitat use, behavior, and breeding biology of the threatened Neosho madtom, NO/lfrus placidlfs, were studied from 1996 to 1998. Two populations of Neosho madtoms were monitored on the Neosho and Cottonwood rivers in Lyon and Chase counties, Kansas. Age and sex structure were investigated
by using length-frequency histograms to determine age-classes and external characteristics to determine the sex offish during breeding season. Two age-classes were observed, which suggests that Neosho madtoms breed at Age 1, Operational sex ratios suggested a female bias in the Neosho River. Young-of-year (YOY) inhabited areas with slower flow, shallower depth, and lower substrate compaction than adults. Breeding adults were more often found in shallower areas with loosely compacted substrate than non-breeding adults. Use of shallow areas with loosely compacted gravel demonstrates the importance of such habitat to these critical life stages, and illustrates the need to protect this habitat for maintenance of populations.
In the lab, effects of photoperiod on behavior were investigated. Individuals held in a long daylight photoperiod spent a higher proportion of time performing cavity enhancement, and courtship behaviors were seen more often in the long daylight photoperiod. The relationship between a long photoperiod and increased cavity enhancement and courtship behaviors demonstrates the influence of photoperiod on the Neosho madtom reproductive cycle. Courtship behaviors recorded included the "carousel" and "tail curl" in which the fish spun in circles head to tail then quivered, with the male's tail wrapped around the female's head. These behaviors were recorded on time-lapse video prior to a spawning event. A second spawning event occurred after two days of injection with synthetic hormone. Both clutches were laid in nest cavities and consisted of approximately 30 eggs. Dissection of the breeding females revealed previtellogenic eggs in their ovaries. Sexual dimorphism during the spawning season was also investigated and differences were described.
