weights when stocked averaged 1.68 grams for catfish and 
1.31 grams for shiners. 
Each pool was lighted by a 300-watt incandescent bulb 
from 6 a.m. to 5 p.m. Because the space available to these 
experiments was poorly heated, water temperatures could 
be maintained no higher than from 72 to 75° F. Both pools 
were continuously aerated and small submersible pumps 
assured a continuous, slow circulation of water throughout 
the pools. 
Results. After 134 days, standing crops in the two di- 
vided pools were equivalent to 2,709 pounds per acre 
(1,838 pounds of shiners, 871 of catfish) where the species 
were mixed, and 2,555 pounds per acre (1,942 pounds of 
shiners, 613 of catfish) where the species were separated, 
having increased from original stocks equivalent to about 
920 pounds per acre (720 pounds of shiners, 200 of catfish). 
This was considered to be a good production rate for shin- 
ers, but catfish growth was limited by water temperatures 
that never exceeded 75° F. 
Fish behavior was observed daily over about the first 30 
days, after which visibility was limited by high turbidity. 
Normal shiner behavior appeared to be a slow, continuous, 
seemingly aimless movement in a loose school. When in the 
same water with catfish the two never mixed except when 
feeding; the catfish remained at the bottom, and the shiners 
were in the upper waters. However, when both fed on meal 
that had sunk to the bottom, they fed and intermixed in an 
apparent state of harmony. 
Catfish behavior changed somewhat with time and in- 
crease in density, and was different when the catfish were 
and were not mixed with shiners. Initial populations of 15 
channel catfish were exceedingly nervous, and when not 
darting wildly about or attempting to hide at the base of the 
divider screen they clustered in a corner, suspended verti- 
cally at mid-depths by slow, continuous tail movements, an 
activity which we called “tailwalking.”” Those catfish not 
associated with shiners tailwalked in the corner quite con- 
tinuously during daylight hours and were not observed to 
feed. Those mixed with shiners appeared calmed by the 
association, tailwalked less, and fed readily. At the first 
feeding on January 12, the shiners fed vigorously as soon as 
the meal hit the surface of the water, and when the meal 
had sunk to the bottom and was being ‘“‘picked”’ by the 
shiners, the catfish joined them, feeding slowly and steadi- 
ly, freely intermixed with the shiners. The catfish re- 
formed their school when the feeding period was ended. At 
such times there appeared to be no species discrimination 
and no antagonism whatsoever between species or individ- 
uals. 
A significant change in the behavior of the catfish oc- 
curred after the numbers were increased from 15 to 50. The 
50 catfish almost continuously maintained their school 
while feeding, sweeping quite rapidly about and appearing 
to “feed on the run.” The school was never observed to dis- 
band and the individuals to feed leisurely while intermixed 
with the feeding shiners, as they had done when they for- 
merly numbered only 15. The moving school occasionally 
caused minnows to scatter out of their path. ‘These near- 
contacts, however, appeared to be inadvertent, and no overt 
antagonism or interference of the feeding of either specie 
was observed. The calming influence of the shiners upo 
the catfish was apparent when the populations were sam 
pled after the initial 2 weeks. The catfish not confined wit 
shiners had lost weight to the extent of about 15 pounds pe 
acre, while those with shiners had gained about 40 pounc 
per acre. At the termination of the experiment, final stanc 
ing crops of catfish averaged 42 percent higher with shine: 
than when physically separated but sharing the same wz 
ter. 
Culture in Aquariums 
Methods.—In a second indoor experiment we used ple: 
iglass and screened containers of identical size (4.5 cub 
feet) to confine channel catfish in equal portions of one 
the 10-foot wading pools previously described. The plex 
glass container, or aquarium, was submerged in the pool : 
that the confined fish were subjected to the same temper. 
ture, light, and water volume as those confined by tl 
screened enclosure, the difference being that the 3/16-inc 
mesh nylon netting permitted a circulation of wat 
through the screened enclosure. We proposed to compa 
growth and behavior of fish in both containers with grow 
and behavior of an identical number of fish free to mo 
about in the total area of the pool. 
Concurrently we established similar experiments wi 
smaller enclosures submerged in a 40-gallon aquarium 
determine if the same response to crowding and the sat 
interspecific relationships were apparent in the small 
water volumes. Unfortunately, the use of such small en’ 
ronments containing clear water proved unsatisfactory, a 
the series did not progress to the use of both catfish ai 
shiners. 
In the first set of experiments we used eight catfish 
each of the three lots in the wading pool and four in each 
the three lots in the 40-gallon aquarium. In all cases t 
fish ate little, if at all, and lost weight. This study was t 
minated after 29 days. 
In a second run in these environments we increased 
number of fish to 24 in each lot in the pool and to 12 in e 
lot in the aquarium. 
Results. —In the aquarium trials all lots again |i 
weight, and that phase of the project was terminate 
These and earlier tests in aquariums seemed to illustr: 
that catfish confined alone in small containers filled w 
clear water do not behave normally, remain nervous, a 
eat poorly. Tests under such conditions are impractical. 
contrast, we have observed that upon transferring cat! 
from a clear aquarium containing only catfish to an ad 
cent aquarium, also clear but containing tilapia, or tila) 
and carp, the catfish became calm and began to feed » 
and grow. The presence of another species of fish appe@! 
to calm, and instill a sense of scurity in, the catfish. 
The wading pool experiment involving three lots © 
fish each was terminated on May 3, after 79 days; with 
results shown in Table 1. The greater growiamm™ the | 
enclosed by glass, with no water circulation, was unexpt 
ed. A possible explanation was that the limited volume 
water in the glass enclosure became quite turbid with f 
