160 FISH CULTURE. 



leaves : the surface of the ponds may, in the autumn, 

 be seen covered with them. The leaves become 

 saturated with water and sink to the bottom of the 

 pond, where they accumulate into a perfect bed, or 

 thick layers of leaves. These, acted on by the water, 

 slowly decompose, the action continuing for months, 

 until they gradually turn into thick, black, and 

 stinking mud. During the decomposition of these 

 leaves, and also after their decomposition, they con- 

 tinue to send forth noisome gases and exhalations, 

 which penetrate and pervade the water, from w T hich 

 an unwholesome mist and smell ascends, more or 

 less at all times, and particularly in hot moist 

 weather. Under these circumstances, how is it possi- 

 ble that the fish inhabiting these waters so affected 

 should be otherwise than receptacles for a species of 

 concentrated essence of mud ? To add to the effect, 

 we leave our ponds year after year without clean- 

 ing them out, and the weeds grow and rot, and grow 

 and rot year after year, and, combined with the leaves 

 from above, the pond literally grows mud, until at 

 length the ponds either so fill up or become such a 

 nuisance that they generate deadly diseases, and neces - 

 sitate a heavy and expensive operation for the carting 

 away of the almost liquid filth thus formed. Ponds 

 cannot be kept too clean, and no more weed should 



