I66 MADRAS FISHERIES BULLETIN VOL. XI, 



difficult to fill them in, they should be drained and attended to 

 similarly to fresh water ponds or stocked with suitable fish as per 

 list given below. 



STREAM BEDS. 



All stream beds should be conserved where they pass through 

 malarial zones. To carry this out effectively the banks require to 

 be given a gentle slope to the normal bed of the stream where the 

 channel should be clearly defined throughout its course within the 

 malarial area. Where the natural flood banks are very wide apart 

 and where hollows exist between them and the normal channel 

 holding water for considerable periods, these should be, if the levels 

 permit, linked up by trenches and drained into the main channel or 

 filled in. If the normal bed of the river is swampy and overgrown 

 with reeds and grass, these should be cleared and an uninterrupted 

 defined course given to the normal stream. Where there is a ten- 

 dency for the river to form a subsidiary deep course during floods, 

 permanent sections to be formed about every lOO feet to prevent 

 future scouring and to facilitate the recovery of the sections of bed 

 if erosion ever occurs. The waters should be stocked with suitable 

 fish larvicides and fishing strictly prohibited. 



Hollows formed by the action of running water and stones on 

 the surface of rocks in river-beds form ideal breeding grounds for 

 mosquitos, where the larvae are free from most of their enemies. 

 These places can often be found black with mosquito larvae, and I 

 would suggest where they exist in malaria-infected areas to have 

 their water holding capacity destroyed. This could be done either 

 by filling in or by dynamite or in most cases with a stone mason's 

 chisel and hammer by simply knocking a drainage channel into 

 each hollow. As it takes many years for these to form, the above 

 measures need not be repeated for a long period. To fill them in, 

 Portland cement would be advisable. 



CASUARINA PLANTATIONS. 



Holes dug for the purpose of obtaining water for young 

 casuarina trees form most dangerous mosquito-breeding places 

 and these can be found in every plantation along the coast. The 

 water from these pits is only required during the dry months of 

 the first two years after planting, and the holes containing water 

 remain for many years afterwards untouched and unused. There 

 is not the slightest reason why these should be allowed to remain 



