Second Series 
Methods.—In a series of eight pools we established two 
replications of each of four different populations that all 
contained the same total numbers of both species, but in 
four different degrees of association (Table 5). The objec- 
tive was to gain additional information on species relation- 
ships and the influence of density. The pools received their 
initial stock on May 29, 1969, and were drained and cen- 
sused on July 23, 1969, providing a growing period of 
55 days. 
TaBLe 5.—Means of final standing crops, in pounds per acre, 
for two replications of each of four different combinations of chan- 
nel catfish (CC) and golden shiners (GS) when maintained out- 
doors in 10-foot-diameter plastic pools over a 55-day growing pe- 
riod. Underlined quantities designate weights of those fishes 
mixed in the same half pool. 
Type of ' ; 
hee Final Weight (Ibs/A) 
tion * GS GS Ee CC Total 
: 7134 1,000 1,734 
754 ¥ 864 1,618 
90 
90 + 32 379 363 1,003 1,745 
16 
16 + 180 2 700 537 391 1,628 
4 Populations contain shiners in lots of 90 or 180 and catfish in lots of 16 or 32. 
b Designates pool containing 32 catfish and 180 shiners intermixed. 
© Designates pool containing 32 catfish separated from 180 shiners by a net. 
Results. —Among the eight shiner populations, differ- 
ences in production were not significant between those con- 
fined in one-half of a pool and those occupying all of a pool, 
or between those directly associated with catfish and those 
sharing the same water with catfish but being physically 
separated from them by a screen. Differences in production 
between catfish populations were larger than those for 
shiners, but still not significant. The differences appeared 
related to predation of shiners by catfish, and this was the 
only experiment in which such predation was evident. 
Gains by catfish were consistently largest when the catfish 
were mixed with shiners, and the data in Table 6 show that 
numbers of unaccounted-for shiners were consistently larg- 
er where mixed with catfish. The differences were statisti- 
cally significant. 
Some calculations were made to provide a basis for eval- 
uating the degree to which predation of shiners by catfish 
might have influenced production of the catfish. Using the 
mean final weight of shiners of 4.28 grams (which would be 
excessive for this computation), assuming that all unac- 
counted-for shiners were eaten by the catfish, and assuming 
a conversion ratio of 1 pound of catfish gain for 2 pounds of 
shiners eaten, predation of shiners would have accounted 
for about 67 percent of the difference in the final standing 
crops of catfish when mixed and when not mixed with shin- 
ers. We believe, however, that the actual contribution of the 
shiners was much less. 
10 
Tape 6.—Numbers of golden shiners that could not be ac- 
counted for at time of final censuses after being mixed or not 
mixed with channel catfish over a 55-day period in 10-foot-diam- 
eter pools. 
Mixed with 
Catfish 
Number Unac- 
counted for 
Type of Pool 
Population * Number > 
c 22 29 yes 
27 52, yes 
d ae) 5 no 
24 8 no 
16 28 39 yes 
16 +189 29 4] yes 
26 E 11 no 
26 W IY yes 
4 Populations contain shiners in lots of 90 or 180 and catfish in lots of 16 or 32. 
b‘“E” beside number indicates east half of pool; ‘“W” indicates west half. 
c Designates two pools, each containing 32 catfish and 180 shiners intermixed. 
d Designates two pools, each containing 32 catfish separated from 180 shiners by 
net. 
Third Series 
Methods.—In this series we again used eight poo 
which had standardized bottom soils and were filled simu 
taneously with water from a common source. We attempte 
to minimize all environmental differences with the purpo 
of measuring those differences in production attributab 
purely to the physical association or separation of the tv 
species. This was accomplished by the common mixing 
water between a pool containing only one of the two speci 
and a second pool containing both species freely mix¢ 
Mixing was accomplished by a slow pumping of the wat 
from one pool to another and returning the same volume 
siphon. The small submersible pumps used transfert 
water at a rate of about 48 gallons per hour and were ¢ 
erated 9 hours each day for 5 days each week. The prin 
pal environmental difference between the paired pools w 
the greater depth of about 1 inch in the pool receiving | 
pumped water, which was necessary to keep the siphon 
operation. Such mixing was intended to minimize the 
ferences of such factors as turbidity, pH, temperatu 
ammonia, and dissolved oxygen between paired pools. 
The pools received their initial stock on July 24, 19 
and were drained and censused on September ie 19 
providing a growing period of about 54 days. Among 
eight pools we had two replications of each of two pair: 
follows: 
1. A pool containing 180 shiners alone sharing circu 
ed water with a pool containing 180 shiners mixed wit! 
catfish. 
2. A pool containing 180 shiners alone sharing circu 
ed water with a pool containing 32 catfish alone. 
Results. —The results of these experiments are presel 
in Table 7 and may be summarized as follows: 
1. The greatest productions by shiners (1,163 and 1 
