66 PREVENTIVE AND REMEDIAL WORK AGAINST MOSQUITOES. 



formosa, is generally to be found with Gambusia and is of the same general character. 

 The females are about one inch long and the males three-quarters of an inch. Both 

 of these species are known as top minnows, from their habit of being constantly at the 

 surface and feeding there. The conformation of mouth, the lower jaw projecting, is 

 evidence of their top-feeding habits. Both of these species are to be found in great 

 numbers in the South in the shallow margins of lakes, ponds, and streams in the tide- 

 water regions wherever there is marginal grass or aquatic and semiaquatic vegetation. 

 They are also to be found in shallow ditches and surface drains where the water is not 

 foul, even where it is but the fraction of an inch deep. In fact, if any fishes will find 

 their way to the remotest possible breeding places of the mosquito, it will be these. 

 And they are the only ones, so far as the writer's observation goes, that can be consid- 

 ered useful as destroyers of Anopheles larvae. 



Gambusia is found in the Ohio Valley as far north as southern Illinois, where the 

 winter climate must be at least as severe as that of the coast of New York and New 

 Jersey. 



Dr. Hugh M. Smith, Deputy U. S. Fish Commissioner, informed the writer that he 

 had examined the stomachs of several hundreds of Gambusia in the Chesapeake Bay 

 and Albemarle Sound waters, and had found the contents to be principally mosquito 

 larvae. * * * 



While, as has been stated, all fishes have some measure of usefulness, if only in the 

 way of deterrent effect, there are only a few species likely to be found in waters in 

 which mosquitoes breed. The most important of these are the gold fish (introduced), 

 several species of Fundulus (the killifishes), and allied genera, three or four species 

 of sunfish, and the roach or shiner, and perhaps one or two other small cyprinoids. 

 In addition, there are a few sluggish and solitary species, like the mud minnow (Umbra) 

 and the pirate perch (Aphredoderus). The sticklebacks have been mentioned in 

 this connection, but the Atlantic coast species, and probably the entire family, are 

 undoubtedly useless for the purpose, being bottom feeders, living in the shallow tide 

 pools and gutters, hidden among plants or under logs and sticks at the bottom, where 

 they find an abundance of other food. 



In the salt marshes there are myriads of killifishes running in and out and over 

 them with each tide, while countless numbers of other and smaller genera, such as 

 Cyprinodon and Lucania, remain here at all stages of the tide. So numerous and active 

 are all of these, that there is no possibility of the development of a mosquito where 

 they have access. 



Of the killifishes two species, Heteroditus and Diaphanous, ascend to the farthest 

 reaches of tide flow, but it is a question as to whether they would prove desirable 

 for the purpose of stocking land-locked waters, since they are a good deal like the 

 English sparrow, aggressive toward the more peaceable and desirable kinds. Even 

 Cyprinodon, which would at first thought be a valuable small species in this respect, 

 is viciously aggressive toward goldfish and no doubt all other cyprinoids. It is so 

 characteristic of all the cyprinodonts, that they can only be kept by themselves in 

 aquaria. They are the wolves or jackals of the smaller species. 



The writer has come to the conclusion, after many experiments in both tanks and 

 ponds, that a combination of the goldfish, roach, and top-minnow would probably 

 prove to be more generally effective in preventing mosquito breeding than any other. 

 The goldfish is somewhat lethargic in habit, and is also omnivorous, but there is no 

 doubt that it will devour any mosquito larvae that may come in its way or that may 

 attract its attention. The one great objection is that they grow too large, and the 

 larger will eat the smaller of them. That is one of the drawbacks to goldfish breeding. 

 There is no danger of overpopulation, but there is of the reverse. Whether or not it 

 is the same with the roach, they are never excessively numerous, although no doubt 

 the most abundant and most widely distributed of the Cyprinidae. They are largely 

 the prey of predaceous fishes, and never approach to the numbers of the killifishes. 



