314 The Philippine Journal of Science i9i5 



fact that in order to clean off the bottom it is necessary to remove 

 the algse would seem to argue in favor of draining off the water 

 only, at the time of removing the fish, instead of scraping the 

 bottom. This will enable the algse to grow at all levels — at the 

 top and bottom, as well as at intermediate regions. 



It has been suggested that an insufficient growth of algae is 

 responsible for poor results around Iba, but the fact that there 

 was a very abundant growth of algae in pond No. 2, of Iba, 

 belonging to Mr. Pio Acayan, helps to solve the difficulty of the 

 other ponds. It was stated correctly that in certain ponds there 

 is not produced sufficient food for the number of fish in the 

 ponds. But the difficulty in these places is that more fish are 

 placed in the ponds than their size justifies. It is necessary in 

 all these ponds to arrive at a correct balance between the number 

 of fish in a pond and the amount of food that can be produced 

 there without exhausting the food supply. 



In order to test the influence of the two kinds of bottoms on 

 the growth of the algal food, a sample of the bottom was brought 

 from each of two ponds in Iba. The first is from that of Jose 

 Venzon, pond No, 1 at Iba, the bottom of which the owner said 

 is too sandy to permit of good growth of algae. This sample was 

 placed in a small aquarium on May 22, with circulating sea water, 

 and on June 4 some small bangos were introduced. Also a mixed 

 algal growth from a pond near Manila was placed in the aquarium 

 on May 22, and two months later the algae were growing very 

 satisfactorily, as also the small bangos. The same conditions 

 were arranged in another aquarium tank, with the difference that 

 a sample from the bottom of Iba pond No. 2 was placed here. 

 The growth of the algae in this second aquarium appears to be 

 equal to that of the first, and the fish, which show great growth, 

 feed equally well here. These observations agree with the testi- 

 mony of different owners of fish ponds in Iba and Subig to the 

 effect that the algal food, lumut, will grow equally well in ponds 

 that at least originally have bottoms of very different proportions 

 of mud and sand. 



By not disturbing the bottoms of these ponds, whether or not 

 at first they have a large or small amount of mud, there will 

 accumulate a layer of "soil" from the breaking down of the algae 

 and a gradual washing in of soil from the sides, which seems to 

 be favorable to the best growth of algae, or lumut. 



The question of the identification of the various algae will not 

 be taken up here, but will be included in another paper dealing 

 with the food of these fishes exclusively. 



