STOCKING. 131 



The ideal conditions required for a spawning Effects of 

 bed are well known — a good and continuous p ° 

 supply of pure water, not varying greatly in 

 temperature, and flowing at a good pace over a 

 clean, bright, sharp, gravel shallow. The supply 

 of pure water and the shallows fit for spawn- 

 ing beds are present in almost all chalk 

 streams ; but unfortunately the hand of man 

 has too frequently, in what he calls the march 

 of civilisation, completely revolutionised the 

 conditions. First, there is a village on the 

 stream, in which the population gradually in- 

 creases ; then some so-called system of 

 drainage is taken in hand, resulting in the 

 poisoning of the river and fouling of the water. 



The mischief does not even cease here, as 

 the presence of sewage stimulates the growth 

 of certain forms of sub-aqueous vegetation, 

 usually the forms least desirable for the food 

 supply of the fish. These weeds choke up the 

 stream, and collect around their roots and stems 

 every particle of earth held in suspension by 

 the water. The weeds in time rot down and 

 become mud, adding to the stratum already 

 deposited in the stream, until at length the 

 bright, fresh gravel is covered to a thickness 

 of many inches with filthy black mud. Any 

 eggs deposited on this mud, if by chance fer- 

 tilised, rarely hatch out, and when they do the 



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