ARTIFICIAL PROPAGATION OF WHITEFISH, ETC. 13 



Clogging through an accumulation of eggshells and impurities 

 in the water may be prevented by an air jet, which can easily be 

 arranged for by installing an air pump and carrying the connect- 

 ing pipe along the side of each tank on the inside of the screen, 

 thence at right angles parallel to the screen and about an inch dis- 

 tant from it. This cross pipe should be perforated on one side with 

 holes one-thirty-second of an inch in diameter and 3 inches apart, 

 the perforations opening toward the screen and upward at an angle 

 of about 45°. When the air is turned on, an apparently solid mass 

 of bubbles will rise along the whole surface of the screen. 



With such an arrangement the screen will need no attention for 

 hours, or even days, at a time, whereas without the air jet one 

 or more men must be employed to keep the screens clear. Moreover, 

 many of the fry are unavoidably killed by being forced against 

 the screens and by the work of the men in keeping them free. The 

 thorough aeration of the water indirectly accomplished by use of 

 the air jet is very beneficial when large numbers of fry are passing 

 over, and twice as many can be safely handled in troughs thus 

 equipped. 



At Put in Bay, where the fry are planted as soon as hatched, 

 they are dipped from the fry tanks into kegs and transported to the 

 natural spawning grounds on the reefs. From 50,000 to 100,000 

 fry are carried per keg, according to the distance to be traveled, 

 and when they are to be carried any considerable distance fresh 

 water is added every hour. 



'V\Tiere facilities are available it is advisable to hold the fi*y in 

 tanks until they have absorbed the yolk sac before planting them, 

 as they are better able at that time to care for themselves than when 

 planted at a very early age. In the spring of 1896 about 1,000 

 whitefish fry were held in a station trough until late in April, with 

 no food supply except the Entomostraca and other minute life 

 coming into the troughs with the water pumped from the lake. 

 The fish attained a considerable growth and were remarkably active. 

 Cannibalism was of frequent, though not of general occurrence. 

 Toward the close of the period through which they were held num- 

 bers were observed to have seized another fry by the tail and swal- 

 lowed as much of the body as possible; this, of course, being very 

 little. In every instance noted a larger fish had attacked a smaller 

 one, the victim being dead and his destroyer swimming about 

 actively with the body trailing along his side. Had these fry been 

 regularly supplied with food it is probable that no cannibalism 

 whatever would have occurred. 



BEABING IN PONDS. 



Few attempts have been made to raise whitefish in ponds, but 

 the experiments conducted lead to the belief that under favorable 

 conditions the species can, to some extent, be reared in artificial 

 ponds, success along this line, of course, implying an abundance of 

 good cold water and suitable ground for the construction of deep 

 ponds. Such an undertaking would not be practical nor feasible 

 at any of the bureau's hatcheries where millions of fish are liberated. 



The outcome of an experiment undertaken in 1882 along this line 

 at the North ville (Mich.) station was successful. Three-year-old 



