ABLE 7.—Numbers recovered and final standing crops, in 
ids per acre, for populations of channel catfish (32) and gold- 
hiners (180) when mixed or separated but sharing water cir- 
ted between populations. Pools having a common water circu- 
yn are paired in the column at left. The populations were 
tained outdoors in 10-foot-diameter plastic pools for 54 days. 
red Pop- Final Standing Crop 
ens anc Golden Shiners Channel Catfish 
riginal Stock Number Pounds Number Pounds 
—_— | 162 1,066 
Se ei70) 1,127 31 1,521 
= = Wie) 1,124 
— in 1,027 33 1,674 
pene} ntz6 1,163 
@) syed 32 1,637 
Sates 171 i S2 
@) =A 32 1,447 
ids per acre) were in those populations maintained 
e in pools sharing circulated water with pools contain- 
atfish only; these averaged less than 10 percent greater 
their companion populations and were not significant- 
ferent from them. 
Greatest production by catfish occurred in those pools 
containing shiners, but there was less than 5 percent 
ovement and this was not significantly greater than 
1 catfish were separated but shared circulated water. 
Near-equal survivals by shiners when mixed and not 
d with catfish showed that predation was not a factor 
is experiment. 
1€ pump and siphon arrangement was not completely 
ent in equalizing measured parameters in the paired 
, but the similarities in standing crops among both 
d and unmixed populations rendered the failure unim- 
int. These results completely substantiated those ob- 
d in tests previously described, namely, that at the 
ities used neither species limited production of the oth- 
hen mixed, and as many total pounds could be pro- 
d by a mixed population in a single pool as by the same 
numbers separated by species in two pools and fed 
ar rations. 
OVERALL DISCUSSION 
ur findings resembled those of Yashouv (1969), who 
1 that growth increments of carp (Cyprinus carpio) 
tilapia (Tilapia aurea) in mixed culture sometimes 
‘ded those exhibited by either in monoculture. 
Ir studies demonstrated that, within the range of sizes 
densities used, the channel catfish, golden shiner, and 
'a (7. mossambica) were extremely compatible. When 
ined, each stimulated the other to a faster and stronger 
feeding response, which resulted in a more efficient conver- 
sion of food. No antagonistic behavior was observed, and 
evidence of significant predation of shiners by catfish oc- 
curred in only one of the six test series studied during the 2- 
year period. While predation of shiners might become im- 
portant if larger sizes of catfish were used, in certain types 
of operations the predation might be minimal or otherwise 
unimportant. If shiners were the primary crop, the ‘“‘bo- 
nus’’ production of catfish could more than compensate 
for such limited predation as might occur, and if market- 
able-sized catfish were the principal crop, it would be of 
small consequence if some of the supplementary crop of 
shiners were eaten. 
There are two basic fish farming operations in which the 
two species could be combined: 
(1) Mix shiner fry with catfish fry, with the purpose of 
producing salable minnows and fingerling catfish. The 
shiners could be spawned in the pond or introduced as mat- 
ted eggs or fry. The channel catfish could be added as fry, 
and Martin (1968) has recommended that such fry be at 
least 1 inch long. It would be advantageous to introduce 
catfish and shiners in approximate known numbers s0 as to 
control the size of the minnows and catfish fingerlings 
grown in this operation. 
(2) Mix shiner fry with catfish fingerlings, with the 
purpose of producing salable bait minnows and channel 
catfish large enough for the food or “‘fish-out’? market. In 
such an operation Martin suggests that the catfish not be 
placed in the pond until the shiners have become advanced 
ity 
Our results in the wading pools suggest that each species 
could be treated as if it were being cultured alone, insofar as 
densities, feeding rations, and final standing crops are con- 
cerned. It should be remembered, however, that at the 
higher densities used in 1969, aeration was required to pre- 
vent oxygen depletion in the pools. The potential for such 
depletion was undoubtedly enhanced by the small size and 
shallowness of the pools which caused abnormally high 
water temperatures and unusually high densities of phyto- 
plankton. Such a tendency might be less in ponds, but it 
still could be a problem if high densities of both species re- 
ceived normal rations in ponds having no water exchange. 
The problem could be eliminated by water exchange, and 
could be greatly lessened by taking extreme care not to ov- 
erfeed the catfish and by feeding the shiners a reduced ra- 
tion. 
The unusual efficiency with which our shiners that were 
mixed with catfish appeared to be converting supplied fish 
meal into fish flesh suggested that they were gaining impor- 
tant and unmeasured nutrients from the abundant phyto- 
plankton. If rich plankton blooms could be produced in the 
absence of full rations for shiners, production of shiners 
might be reasonably high with a minimum shiner ration 
while maintaining a normal production of catfish on nor- 
mal catfish rations. 
Two principal problems in such a combined culture 
would be the danger of oxygen depletion because of the in- 
creased organic load, as already discussed, and the difficul- 
ties in harvesting the shiners without mechanical injury 
11 
