In a later collection (2 June, 1958), numbers present on the riffles were greatly reduced and the larger individuals were almost entirely missing. Some of the smaller individuals were still present in the shallower riffle areas. Table 7 compares sizes of the individuals obtained on 2 June with sizes collected from deep riffles at the middle Neosho station on 7 June, 1958. The larger size of the group present in deep riffles is readily apparent. The yearlings almost completely disappeared from subsequent collections on riffles.
A bimodal size-distribution of young-of-the-year was noted also in 1958 and 1959; but, no segregation of the two sizes occurred on riffles in summer. Marzolf (1957:25) recorded two peaks in spawning activity in Missouri ponds. Two spawning periods may account for the bimodal size distribution of young-of-the-year observed in my study.
In 1959, young-of-the-year began to appear in the latter part of June and became abundant by the first part of July. Individuals as small as one inch T. L. were taken in gravel-bottomed riffles on 1 July, 1959.
Yearling individuals at the lower and middle Neosho stations showed a pronounced tendency to move into shallow, moderately fast water over rubble or gravel bottom at night, where they were nearly ten times more abundant than in daytime (Table 9). Adults probably have the same pattern of daily movement as yearlings, except that at night the adults move to deeper riffles. Bailey and Harrison (1948:135-136) demonstrated that channel catfish feed most actively from sundown to midnight.
Channel catfish (especially two-year-olds and adults) were abundant on a rubble-riffle during the day in some collections at the lower Neosho station in 1959.
Table 7. Length-frequency of Channel Catfish from the Neosho River, 1957, 1958 and 1959. (Numbers in Vertical Columns Indicate the Number of Individuals of a Certain Size Collected on That Date.)
| Length in inches | Nov. 2 1957 | June 2 1958 (shallow riffle) | June 7 1958 (deep riffle) | Sept. 9 1958 | Sept. 11 1959 |
|---|---|---|---|---|---|
| 1.5 | 1 | ||||
| 2.0 | 3 | ||||
| 2.5 | 13 | 2 | 1 | 2 | |
| 3.0 | 4 | 11 | 3 | 4 | |
| 3.5 | 3 | 21 | 7 | 1 | 14 |
| 4.0 | 11 | 12 | 9 | ||
| 4.5 | 4 | 10 | 1 | ||
| 5.0 | 2 | 11 | 2 | ||
| 5.5 | 1 | 7 | 26 | ||
| 6.0 | 58 | 2 | |||
| 6.5 | 1 | 32 | 5 | ||
| 7.0 | 16 | 5 | |||
| 7.5 | 1 | 4 | 5 | ||
| 8.0 | 22 | ||||
| 8.5 | 45 | ||||
| 9.0 | 81 | ||||
| 9.5 | 41 | ||||
| 10.0 | 21 | ||||
| 10.5 | 8 | ||||
| 11.0 | 4 | ||||
| 11.5 | 1 | ||||
| 12.0 | 3 | ||||
| 12.5 | 1 | ||||
| 13.0 | 1 |
Near the end of the spawning season in 1959, I found spawning catfish at the lower Neosho station. Ripe females were taken between 9 June and 30 June, 1959; and, on 19 June I found a channel catfish nest with eggs (water temp. 79° F.). The nest-site was a hole in the base of a clay bank; the floor was clean gravel with a small mound of gravel at the entrance. The nest-opening, five to six inches in diameter, widened almost immediately into a chamber about two and one-half feet long and one foot wide. Normally the water was about six inches deep in the mainstream as it ran over a riffle adjacent to the catfish nest. When I put my hand into the opening the fish bit vigorously, but became quiescent when I stroked its belly. I then felt the rounded gelatinous mass of eggs on the bottom of the nest. On June 22 (water temp. 86° F.) the fish was removed, struggling, from the nest, and returned to the stream. The next day (23 June 1959, water temp. 84° F.) the eggs had hatched and the young were in a swarm in the nest. The adult did not attempt to bite but left as soon as I put my hand into the hole.
Marzolf (1957:25) reports that young remain in the nest from seven to eight days after hatching. My seining records show a marked increase in abundance of small young-of-the-year on the first of July. Probably the time of hatching of the nest described above correlated well with hatches of other nests.
One and sometimes two channel catfish were found in other holes in the stream-bank or bottom. The fish occasionally attacked my hand vigorously, but at other times remained quiet or left without attacking. No other channel catfish eggs were found, although one hole under a rock in the middle of the river had one or two individuals in it each time it was checked until 11 July, 1959. A local fisherman informed me of his belief that these holes are occupied only in the spawning season.