Taste 1.—Original and final weights and gains over a 79-day 
eriod for three lots of channel catfish under different conditions 
[ confinement in a 10-foot-diameter plastic pool. The pool was 
jaintained indoors. 
———— 
Weight (grams) 
ype of When At Final Percent 
)pulation Stocked Census Gain Gain 
ee in pool 47.4 66.0 18.6 Se 
ynfined by net 45.4 60.0 14.6 622 
mfined by glass 41.0 70.0 2980) 70.7 
id wastes, whereas the other waters remained clear. It is 
sumed that catfish obscured in the darker, turbid water 
re less nervous and were able to make more efficient use 
available foods than their companion lots in the clear 
ter. Concentrations of ammonia went to a maximum of 
3 ppm in the glass enclosure and averaged 0.83 ppm for 
readings over the experimental period; in the open pool 
maximum was 0.34 ppm with an average of only 0.16. 
l€ greater concentration of ammonia in the glass enclo- 
€ occurred at relatively low pH values (mostly between 
and 8.0) and apparently had no limiting effects. 
OUTDOOR EXPERIMENTS IN 1968 
st Series 
Methods.—The first series of outdoor experiments in- 
ved 20 pools containing two replications of each of 10 
erimental populations, as illustrated in Table 2. The 
ls were arranged in three rows, with a separation of 
ut 2 feet between pools. The location of individual pop- 
tions within the arrangement of pools was established 
random selection. Water was maintained at a depth of 
ut 21.6 inches, providing a volume of about 1,057 gal- 
. The pools were provided with soil substrates, as pre- 
isly described. 
erage total lengths and weights of the fishes when 
ked were about 140 mm and 19 grams for catfish, 57 
and 1.32 grams for the shiners, and 66.1 mm and 5.09 
ms for the tilapia. A ration equal to 3 percent of the 
ht of the fish was fed once each day for 5 or 6 days each 
k. The pools were stocked over the 3-day period June 
20, 1968 (catfish on June 18 and 19, and shiners and 
ia on June 20) and the study was terminated on Sep- 
er 11. Thus the growing period ranged from 83 days 
shiners and tilapia to 85 for catfish, but for practical 
ses it has been computed as 84 days for all species. 
esults.—Catfish mortalities were either catastrophic, 
hen oxygen was depleted, or insignificant. In both 
lations in which 16 catfish were intermixed with shin- 
and in one where 16 catfish were separated from the 
rs by a screen, total mortalities were suffered too late 
€ experiment for the fish to be replaced, and no final 
us data could be recorded (Table 2). Among the 13 
lations that provided usable data, only 10 catfish were 
ved dead and replaced during the experiment. All 13 
“se populations were intact, containing either 8 or 16 
iduals, at the termination of the study. 
iner mortalities were high following initial stocking, 
gradually lessened over the first 30 days, and were quite 
insignificant thereafter. Rates of mortality were similar in 
all populations. Dead shiners floated and were replaced 
daily where separated from the catfish, but were not missed 
or replaced until the time of the biweekly sampling period 
when they were mixed with the catfish. If the shiners were 
eaten by the catfish, it probably occurred after the shiners 
had died, because mortalities were again approximately 
equal in all populations during the later period when very 
few deaths occurred in any pools. It seems unlikely that the 
catfish would have preyed upon living shiners during the 
first month but not in the last two. Growth curves do not 
indicate that the catfish mixed with shiners had a greater 
advantage during than after the period of high shiner mor- 
tality. 
Our production data gain some perspective in Table an 
which presents final standing crops of all populations in 
terms of pounds per acre, together with the ranges and sea- 
sonal averages of pH, turbidity, ammonia, carbon dioxide, 
and total alkalinity. These data show that (1) standing 
crops of catfish were highest in weight when they were 
maintained alone in an entire pool, but only about 10 per- 
cent higher than when the same numbers of catfish were 
confined to one-half of a pool or when mixed with shiners 
and tilapia in an entire pool, (2) standing crops of shiners 
were consistently and significantly (.05 level) higher in 
weight when in direct association with catfish, or with cat- 
fish and tilapia, than when maintained alone, as empha- 
sized by the fact that 45 shiners mixed with catfish made a 
greater gain than 90 shiners maintained alone, (3) shiners 
and tilapia increased total fish production while scarcely 
affecting catfish production, and (4) when all three species 
were combined at the lower stocking rate of 8 catfish and 45 
shiners, mean production of catfish was about 14 percent 
higher and total production was 42 percent higher than in 
mixtures containing only catfish and shiners. 
In Table 2 we may also observe that in general the high- 
est production by both catfish and shiners occurred in those 
pools having the highest levels of turbidity, ammonia, and 
carbon dioxide. We suspect that the higher levels of ammo- 
nia and carbon dioxide were the result, rather than the 
cause, of higher fish production. It seemed clear, however, 
that both fish density and turbidity influenced production 
and that the two were inseparably related. Catfish produc- 
tion appeared to be most strongly influenced by density or 
availability of space, while shiners appeared to be more 
strongly influenced by turbidity or density of phytoplank- 
ton. For example, gains by catfish having access to entire 
pools were always higher than gains by similar numbers 
confined to halves of pools; these differences were signifi- 
cant at the .05 level. On the other hand, gains by shiners 
were greatest where turbidities were greatest, regardless of 
whether they had access to all or only one-half of a pool, 
and this correlation (r = .901) between high shiner produc- 
tion and high turbidity was significant at the .01 level. 
It was additionally clear that high turbidity occurred 
only in the presence of catfish. The level of turbidity was 
related more to the area of bottom available to the catfish 
than to the number of catfish, the presence or absence of 
