The orangethroat darter was less restricted in habitat than the johnny darter, occurring in all stream-types, but most often in the riffles of gravelly streams. Most specimens from muddy or sandy streams were small.
Aplodinotus grunniens Rafinesque, freshwater drum. Stations 3-S, 4-S, 6-S, 7-G, 8-S, 15-S, 38-S, 39-S, 53-S, and 56-S.
The ages and calculated total lengths at the last annulus for 42 freshwater drum from the Big Blue River were: I, 3.0 (10); II, 5.7 (6); III, 9.4 (7); IV, 12.1 (13); V, 14.0 (3); VI, 15.1 (2); and VII, 16.3 (1).
HYBRID COMBINATIONS
I obtained two hybrid fishes in my study-area. One specimen of Notropis cornutus frontalis × Chrosomus erythrogaster was taken at Station 29-G. This combination was recorded by Trautman (1957:114) in Ohio. The other hybrid was Lepomis cyanellus × Lepomis humilis, captured at Station 24-G. This combination was first recorded by Hubbs and Ortenburger (1929:42).
Hubbs and Bailey (1952:144) recorded another hybrid combination from my area of study: Campostoma anomalum plumbeum × Chrosomus erythrogaster, UMMZ 103132, from a "spring-fed creek on 'Doc' Wagner's farm, Riley County, Kansas; September 21, 1927; L. O. Nolf [collector]."
RELATIVE ABUNDANCE AND DISCUSSION OF SPECIES
The relative abundance of different species was estimated by combining counts of individual fishes taken in 290 seine-hauls, 26 hours and 15 minutes of shocking, and seven samples obtained with rotenone. At some stations all seine-hauls were counted. At other stations the seine-hauls in which complete counts were recorded had been selected randomly in advance; that is to say, prior to collecting at each station. I selected those hauls to be counted from a table of random numbers (Snedecor, 1956:10-13). I did not use the frequency-of-occurrence method as proposed by Starrett (1950:114), in which the species taken and not the total number of individuals are recorded for all seine-hauls. However, the frequency of occurrence of each species is indicated by the number of stations at which it was found, and those stations are listed in the previous accounts. [Table 3] shows the percentage of the total number of fish that each species comprised in three kinds of streams: sandy (Big Blue and Little Blue rivers), muddy, and gravelly streams.
The habitat preferences of some species affect their abundance in different stream-types. Notropis lutrensis and P. mirabilis seemed almost ubiquitous. Notropis deliciosus also occurred in all kinds of streams (rarely in muddy streams); however, this species was represented by the sand-loving N. d. missuriensis in the Big Blue and Little Blue rivers, and N. d. deliciosus in the clear, gravelly, upland creeks (Nelson, personal communication). Because of its widespread occurrence, and for purposes of later discussion, I refer to this minnow also as an ubiquitous species in the Big Blue River Basin.