508 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [42] 



fisheries. Fish of prey, like pike, &c., need a still greater quantity of 

 water and consequently a still larger fish-pit. As not only the success 

 of the fisheries, but also the safety and well-being- of the fish during 

 winter, depends on the proper construction of the fish-pit, it should be 

 carefully constructed and kept scrui)ulously clean. 



5. THE OUTSIDE PIT. 



In order to catch those fish, which, in spite of all precautionary meas- 

 ures, such as grates, nets, &c., escape through the outlet pipes, a de- 

 pression corresponding to the fish-pit should be constructed on the 

 land side of the dam, where the water leaves the outlet pipes, so that the 

 fish may be gathered and caught in it. This depression is called the 

 outside pit. It should be closed against the outer outlet ditch by a 

 narrow grating. This will be all the more necessary if below the main 

 pond there are spawning or growing ponds which are fed from it, so as 

 to prevent fish of prey from entering them. The grating is not only 

 intended to prevent the food-fish from escai)ing, but also to retain small 

 fish which are used for feeding the fish of prey in the main ponds or 

 tanks. The outside pit should always have a depth of water sufiicient 

 to keep the pipes under water, as only thus will they last for centuries, 

 while, laid dry and exposed to the air, they will soon decay. The size 

 of the outside pit will be regulated by the size and location of the i)ond, 

 as well as by the quantity of fish it is expected to hold. With large 

 I)onds the outside pit is generally a square hole in the ground lined 

 with wood. 



(3. DITCHES FOR THE SUPERFLUOUS WATER. 



Whenever streams or brooks pass through a pond, it will be neces- 

 sary to place a weir with locks in these streams or brooks, so that the 

 necessary quantity of water nuiy at any time be let into the pond, while 

 the superfluous water must be carried away through ditches. This will 

 be necessary particularly in mountain streams, as during heavy rains 

 they will carry a great deal of gravel, small stones, and mud, which 

 would soon obstruct the pond. Such waters should be caught outside the 

 pond, or the weir, in the ditches which carry it round the pond, so as to 

 join the stream again below the pond. The ditches for the superfluous 

 water should be of sutficient breadth and depth to receive the quantity 

 of water which may be expected. They should be carefully constructed, 

 as irregular sides are much more exposed to the destructive force of the 

 water than smooth ones. For better protection it will be well to plant 

 the sides with willows. Wherever the tap system is employed, the out- 

 let pipes are, after the water in the pond has been raised to its normal 

 height, closed by a tap, which is not drawn till the fisheries commence, 

 unless special circumstances should require it. In small ponds, whose 

 supply of water is, as a general lule, small, and at times interrupted — 

 as is specially the case with sky ponds — it will be necessary, in order to 

 keep the water at its normal height, that a suitable means of escape 



