PLANKTON PRODUCTION IN FISH PONDS 
157 
PPM. 
C 4. Table 8 shows that the control pond, C 4, contained a greater variety of 
algae than either C 2 or C 3, but that none of the algae that were present in C 4 occurred 
in very large numbers. Scenedesmus was present in all but one sample from this 
pond, but the maximum number of colonies per liter of water was only 123,000. 
This is in marked contrast to the maxima for C 1, C 2, and C 3, as shown in Table 
8. Single cells of Chroococcus occurred regu- 
larly, but here again the maximum was only 
210,000 cells per liter. Aphanizomenon was 
more abundant in C 4 than in C 1, but it was 
far less abundant than in C 2 and C 3. Oocystis 
was present in all samples except the first, but 
the numbers per liter are not comparable to 
those for C 2 and C 3. The rest of the alga 
that were found were present in small numbers 
only. It may be mentioned here that Eudorina 
occurred once in this pond. This is the only 
instance in which colonial flagellates were found 
in this series of ponds, outside of C 1. 
In Table 9 there is given a summary of 
the dominant algae in the centrifuge plankton 
for the four C ponds. This table shows a marked 
contrast in the abundance of algae in the fertil- 
ized ponds as compared with their abundance in 
the control pond. It emphasizes, likewise, the 
difference in the types of algae that are domi- 
nant in C 2, C 3, and C 4, and those that are 
dominant in C 1. The table shows that the 
dominant algae in C 1 were colonial flagellates, 
whereas the dominant algae in the other three 
ponds were the blue-greens, Aphanizomenon 
and Chroococcus; the greens, Oocystis and 
Scenedesmus; and the diatom, Svnedra. 
The relationship between the fluctuations 
in the number of algae and the amount of or- 
ganic matter has been referred to in the discus- 
sion of the latter. 
SUMMARY 
It was stated at the beginning of this sec- Figure 6. — Variations in free carbon dioxide, dis- 
tion that the object of the experiments in the solved oxygen, chloride, different forms of nitro- 
gen and phosphorus, and organic matter expressed 
C ponds W£LS to determine the effectiveness of in p. p. m.; pH values and temperatures in de- 
soybean meal, shrimp bran, and superphosphate grees c ' for pond D 9 
as pond fertilizers. The results, as presented in Tables 4, 6, 8, and 9, show that 
each one of these fertilizers had a beneficial effect on plankton production. This is 
evidenced by the larger amount of organic matter in the centrifuge plankton, the 
larger volume of net plankton, and the greater number of algae in the centrifuge 
plankton from the fertilized ponds as compared with the control pond. Which 
