fi08 EEPORT OF THE COMMISSIONER OF FISHERIES. 



that ever-present cosmopolitan pest, the mosquito. Howard (1901, 

 p. 161) emphasizes the importance of lish in this respect and gives an 

 instance where carp are said to have been very effective, though he him- 

 self doubts whether carp could have been the fish that destroyed the 

 larva?. He says: 



It was stated a number of years ago in Insect Life, that mosquitoes were at one 

 time very al)undant on the Riviera in South Europe, and that one of the Enghsh 

 residents found that they bred abundantly in the water tanks, and introduced carp 

 into the tanks for the purpose of destroying the larvie. It is said that this was done 

 witli success, but tiie well-known food- habits of the carp seem to indicate that there 

 is something wrong with the story. If top-minnows or sticklebacks had been intro- 

 duced, however, the story would have been perfectly credible, and it points to the 

 practical use of fish under many conditions. Some years ago Mr. C. H. Russell of 

 Bridgeport, Conn., described a case in which a very high tide broke away a dike and 

 flooded the salt meadows of Stratford, a small town on the north side of Long Island 

 Sound. The receding tide left two small lakes neai ly side by side and of the same 

 size. In one lake the tide left a dozen or so small fish, while the other was Ashless. 

 An examination by Mr. Russell in the sunnner of 1891, showed that while the Ashless 

 lake contained tens of thousands of mosquito larvae, that containing the fish had no 

 larvse. « 



From the results of the stomach examinations recorded in the earlier 

 pages of this report it does not seem that Howard"'s conclusion that 

 carp did not destroy the larvt« in the tanks in question is warranted. 

 While it is true that no mosquito larvae were found among the intes- 

 tine contents examined in connection with the present investigation, 

 this ma}^ have been due to their small size; the fact that in some 

 cases the food of the fish seems to have consisted almost entirely of 

 insect larvae makes it probable that those of the mosquito would be 

 taken as well. Since it is reasonable to suppose that there was little 

 or no other food in the tanks mentioned in the above quotation, it is all 

 the more probable that the carp would there have eaten the mosquito 

 larvae, and I see no reason to doubt the original statement. It may 

 well be that among our native fish there are some species, such as the 

 stickleback and top minnow, which are better adapted to this purpose 

 than the carp, but the latter is not for this reason a negligible factor. 

 Undoubtedly many ponds that annually breed millions of mosquitoes 

 need only to have plenty of fish introduced in order to abate the 

 nuisance. If carp will do this as well as other fishes, it will serve a 

 double purpose, as it can also ])e used for food. 



Another, and perhaps even greater, benefit to be derived from the 

 presence of carp has recently been suggested in a bulletin by Doctor 



o In February and March, 1904, 1 had similar opportunity to observe the efficacy of flsh in keeping 

 the waters where they are present free from mosquito larvae. About the hacienda at Chichen-Itza, 

 Yucatan, there are a number of large tanks which are kept constantly filled with water for the slock 

 and for other purposes. In some of these tanks mosquito larvse were very abundant; but in the 

 others, into which a few small native fish, locally known as "mojarras" {_Heros urophthfflmus) , had 

 been introduced, none were to be found. The same was true of two natural pools in the vicinity 

 where these fish lived, while, on the other hand, large numbers of larvae could be found in small 

 hollowd in the rock and other places where the rain water had been standing for a few days. 



