PLANKTON PRODUCTION IN FISH PONDS 
161 
Rotifera, Anuraea, Asplanchna, Brachionus, Polyarthra, and Triarthra were the 
most common. Anuraea was present in two-thirds of the samples and reached a 
maximum of 465.0 per liter on June 9. Asplanchna occurred only in one-third of 
the samples, but attained a maximum of 651 per liter on May 29. Brachionus 
occurred in three samples having a maximum of 25.5 per liter on May 19. Polyar- 
thra was found regularly during June and September. It was present, also, in one 
sample for July and in one for August. The maximum of 65.2 individuals per liter 
occurred on June 30. Triarthra occurred three times — twice in May and once in 
June. The maximum number of 28.5 per liter occurred on May 19. The genera 
Monostyla, Rotifer, Noteus, and Rattulus were at different times represented by a 
few individuals. 
Centrifuge 'plankton . — All the algse in the centrifuge plankton have been enumer- 
ated, but only the principal ones are taken up here. The number of algse, on the 
whole, is very low. Among the Myxophycese, Aphanizomenon was the most im- 
portant one. But even it did not occur in anything like the numbers that are given 
below for D 9. The maximum for Aphanizomenon in D 4 is 14,400 filaments per 
liter. Of the Chlorophycese, Oocystis and Gloeocystis were by far the most abundant. 
Oocystis occurred in a majority of the samples, but only in relatively small numbers, 
the maximum being 10,400 cells per liter. This number was present on June 20. 
Sjmedra is the only diatom that occurred in considerable numbers. The maximum 
for this alga was 48,100 cells per liter. This number was present on May 9. None 
of the Peridiniae occurred in significant numbers. 
POND D 5 
The pond D 5 had not been in use for several years and, therefore, was in a sense 
a new pond. It had been wintered dry and was not fertilized. The water was turned 
into this pond during the last w o eek of April. 
NOTES ON VEGETATION 
May 15: Cattails ( Typha latifolia) abundant all over the pond. 
May 26: Cattails (Tiypha latifolia ) abundant all over the pond. 
June 16: Cattails covered approximately 80 per cent of area. Various grasses cover large area of 
bottom. 
June 30: Cattails cover about 85 per cent of area. Land plant and spear grass present. 
July 23: Cattails cover about 50 per cent of area. Elodea, blanket, algse, land plants and grasses 
present. 
August 16: Cattails cover about 60 per cent of area; grasses and land plants, 25 per cent of area. 
Some blanket algse (Hydrodictyon). 
LIMNOLOGICAL DATA 
The limnological data are shown in Table 10. 
The range in temperature is very similar to that recorded for D 4. The minimum 
spring temperature of 13.3° C. occurred on May 19. The maximum summer tempera- 
ture of 27.8° C., occurred on June 30. By September 29 the temperature was down 
to 11.1° C. 
A study of Table 10 shows that the water in pond D 5 was more transparent 
than in D 4 and D 9. The minimum transparency was 3 feet. When the trans- 
parency reached a maximum, the bottom was visible. The greater transparency of 
the water in this pond is due, at least in part, to the small amount of plankton. 
