50 



but continues into July in northern Minnesota. The 

 nesting season for any one locality usually lasts about 

 3 weeks. 



As soon as the chubs in the raceway are through 

 spawning (no activity on the beds for 2 or 3 consecutive 

 days with water temperature 55° P. or higher), they 

 should be removed from the stream and bas.e pool. If 

 no young fish ( fry ) have appeared, all structures in 

 the raceway can be removed; the adult fish in hiding 

 can be driven into the base pool, which in turn can be 

 drained, and the adults easily removed. However, if 

 fry are present, the breeders will have to be driven 

 from the stream and taken by seine in the base pool. 

 As soon as the brood stock is removed, fry screen 

 (60-gauge), if not installed earlier, should be placed 

 in the outlet. Within 10 days after the breeders have 

 been removed, more sluice boards can be placed in the 

 outlet to raise the water level to normal pond height 

 and innundate the entire spawning raceway. As soon as 

 the pond is filled, the incoming flow can be reduced to 

 a point just sufficient to maintain a constant level. 

 If the raceway is not constructed within the basin of 

 a pond, the incoming water supply should not be reduced 

 until all the eggs have hatched and the fry have moved 

 into the base pool, a process which normally would 

 require anestimated 20 days after cessation of spawning 

 activity. 



As soon as the fry concentrating in the base pool 

 become conspicuous and are grouped in schools along 

 the shore, they can be collected with a bobbinet seine 

 and transferred to rearing ponds. It is almost impos- 

 sible to make an accurate count of the number of fry 

 collected other than by hand-counting, which would be 

 an endless job. About the only method which could be 

 used for estimating numbers would be to concentrate a 

 stock of fry in a container, such as a tub, and remove 

 these with a quart dipper in which the estimated number 

 per dipper had already been determined. Naturally, 

 there would be a considerable error involved. 



STOCKING OP PONDS AND MINNOW PRODUCTION 



Information on the stocking of ponds with chub fry 

 is meager. In Michigan, a survival rate of more than 

 50 percent was recorded in ponds stocked with 20— day- 

 old fry. One pond, stocked at the rate of 39,000 fry 

 per acre, produced about 9,000 salable minnows in a 



