l62 MADRAS FISHERIES BULLETIN VOL. XI, 



To go to the opposite extreme (which I learn has been done in 

 some cases) of putting oil and cresol into ponds where fish existed, 

 is most unwise and fatal to other small life as well as larvae. In 

 the first place you not only destroy the fish, but also all small 

 under-water life including other valuable (minute) larvicides, and 

 secondly the effect of cresol and oil is only of a temporary nature 

 and, if not regularly repeated, the pond, etc. so treated becomes a 

 doubly dangerous mosquito-breeding ground. 



From a piscicultural point of view the introduction of poisonous 

 substances into waters where fish can be used should be strictly 

 prohibited. The trouble of clearing surface weeds or conserving 

 ponds,, etc. is infinitely less than repeated cresoling and oiling and 

 the benefit of the former has the advantage of being more perman- 

 ent. The cresol and oil treatment is most excellent for, and should 

 be confined to, small isolated puddles or pools too small or of too 

 temporary a character to stock with fish. 



SUGGESTED TREATMENT FOR PONDS. 



When introducing fish into ponds for purposes of destroying 

 mosquito larvse, it is necessary to conserve such waters by the 

 removal of surface weeds and floating debris near the margins and 

 draining or filling in isolated pools near the foreshore. The value of 

 this conservancy became apparent to me during my earliest experi- 

 ments with fish as larvicides. The ponds which were selected for 

 the first experiments were comparatively clear of surface weeds and 

 floating debris and mosquito larvae could be found near the margin. 

 They were stocked with larvce-eating fish and after a few days 

 were thoroughly examined with the result that no larvae could be 

 traced excepting above some patches of surface weed ; this weed was 

 promptly removed and a further search was made the following 

 day with a negative result. 



The margin of ponds, etc. should be trimmed and over-hanging 

 plants that reach to the surface of the water should be cut back, as 

 these tend to hold up debris and protect the larvae. All small 

 isolated puddles should be filled in or drained. It is just as easy 

 to keep a neat margin to a pond as a neat border to a garden. 



BURROW PITS. 

 The depressions formed when constructing the bunds of irriga- 

 tion tanks, railways, etc. in India form extensive breeding grounds 

 for mosquitos. The best method I think of dealing with these 



