MISCELLANEOUS NOTES. 1165 



the word " plumbicolor" his choice is unfortunate for the descriptive word 

 should apply to some evident, permanent characteristic, while as far as I 

 have observed the keelbacks, the plumbaginous belly scales disappear with 

 age. 



T. M. EVANS. 

 Panchgani, 1th January 1911. 



No. XXIV.— MOSQUITOS AND FISH. 



The fact that fish devour the larva of mosquitos has attracted the 

 attention of several observers in Bengal in recent years. At first sight 

 this habit of fish does not appear to be of much significance. Mosquitos 

 and fish as well as malarial parasites have all been living in Bengal for 

 some time past. But the fish have become important in this connection, 

 because of certain circumstances which are believed to appertain to the 

 island of Barbadoes. 



It is said that there is no malaria in Barbadoes, because there are no 

 mosquitos there. Mosquitos cannot live because all the fresh waters are 

 swarming with a small fish called " the millions," which would devour the 

 larvae if they were present. It is evident that the millions do not devour 

 mosquito larvse in Barbadoes, they have not the opportunity. 



The absence of malaria and mosquitos and the presence of " the millions" 

 may, for the sake of discussion, be called the narrative concerning malaria 

 in Barbadoes. There is no reason so far as I know for believing that this 

 narrative is untrue, but it is evident that before any steps are taken in 

 India to fight malaria by means of fish, we ought to be quite sure that it 

 is true. 



If the narrative is true, there is something very remarkable about the 

 fish called " millions." In nature there is a balance between the numbers 

 of any species and the amount of food that is available for their nutrition. 

 Population is diminished by famine and increased by plenty, this is no 

 less true of fish. A given volume of natural water cannot support more 

 than a certain weight of fish. 



If then the fresh waters of Barbadoes are constantly swarming with a 

 particular kind of fish, that kind of fish must have some special source of 

 nutriment. Most fresh waters in the world contain fish but not in swarms. 

 If the millions are able to live in swarms in any kind of tropical pond, it is 

 evident that they ought to be introduced into malarial regions. 



But it is most unlikely that a species of fish can exist in vast numbers in 

 any kind of fresh water, if it has this power it must have a special method 

 of extracting nitrogenous food out of pond water, a secret which it does not 

 share with other animals. The suggestion has been made that in Bengal 

 the fish Hapockilus pancha.r should be encouraged to play the part of the 

 Bi 



