76 PISH FARMING : 



it, and of the right sort, is absolutely necessary to fish life ; 

 without it, fish-farming operations spell failure. And not only 

 do the fish require food, but that food itself requires food. 

 Hence it follows that a ewd larder must be kept, and grazing 

 ground provided for the filling of it. And this brings us to 

 the subject of aquatic plants. 



Aquatic plants have many uses on a fish farm. 'They not 

 cnly form natural preserves in which the food of trout can be 

 produced in enormous quantities, but they also provide shade 

 and shelter for the fish, and, in many cases, are invaluable in 

 connection with the maintenance of a plentiful supply of 

 oxygen in the water; for all aquatic plants, more or less, con- 

 sume carbon gas, which, if present in sufficient quantity in ^ny 

 water, spells death to all trout. Moreover, in the process of 

 consuming carbon they set free oxygen, and thus provide iish 

 life with an increased quantity of that life-giving element. 



Without hesitation I place the common watercress ^Nastur- 

 tium officinale) in the premier position of all aquatic plants 

 on fish-farms. The value of its presence in large quantifies 

 cannot be over-estimated. Useful everywhere, it is invaluable 

 in the stream that supplies the fishery with water; in the dis- 

 tributing ponds' at the head of the rearing ponds and redds ; on 

 the redds ; and at the shallow parts and edges of the ponds ; 

 in the fenced potions of river or stream, and in special ponds 

 alternating with rearing ponds or redds. Water benefits 

 immensely by passing through beds of watercress ; young fry 

 delight in the shelter it provides, and thrive on the large quan- 

 tities of food inevitably associated with its growth; and 

 mature fish profit by its presence in a proportionate manner. 

 So very useful is this plant that I recommend its introduction 

 wherever possible. On the banks of some big, deep rivers, 

 unsuitable in themselves for the promotion of its growth, 

 suitable ponds for its reception may be made, and a sufficiency 

 of water permitted to flow from the river, through the water- 

 cress bed, and into the river below, with marked beneficial 

 results. That the fish appreciate the presence of these beds of 

 cress is amply proved by the fact that they congregate at the 



