REARING YOUNG SALMONOID FISHES. 223 



into some small ponds in which yearling and older fish are kept; but there is one 

 system of 52 troughs arranged in four series, which use in succession the same water. 

 From these we have learned that young salmon thrive quite as well in tlie fourth 

 series as in the first. Indeed, by an actual test, with fish of like origin and character 

 in each series, the fish reared in the fourth series were found to grow faster, to an 

 important degree, than those in the first. This phenomenon probably resulted from 

 a somewhat higher temperature which the water acquired in passing through the 

 several series. A like observation has been made on a few salmon maintained for a 

 few weeks in the warmer water of a neighboring brook. 



As already stated, the activity of the station has been mainly occupied with 

 Atlantic salmon, but there have been reared each year a few landlocked salmon and 

 brook trout, and occasional lots of other salmonoids, such as Loch Leven, Von Behr, 

 Swiss-lake, rainbow, and Scotch sea trout. All these have received the same treat- 

 ment. With the exception of the rainbow trout, they are all autumn-spawning fishes, 

 and their eggs hatch early in the spring. 



The embryos of salmon begin to burst the shell in the month of March, and the 1st 

 of April may be stated as the mean date of hatching. If the open-air troughs are in 

 order — and we aim to have them so — the eggs are counted out into lots of 2,000 or 

 4,000 each and placed before hatching in their summer quarters. The water is at that 

 time very cold, the development of the alevins is slow, and it is not until the latter 

 part of May that the yolk sack is fully absorbed. June 1 is, therefore, the date when 

 feeding is ordinarily begun. The growth of the fish is at first slow, the water being 

 still cool, but is accelerated as the summer passes away. In October and November, 

 beginning commonly about the middle of October, most of the fish are counted out and 

 liberated, but a small number, rarely more than 15,000, being carried through the 

 winter at the station. 



The reserved fish are sometimes left until midwinter in their summer quarters, 

 and with a careful covering of the conduits and banking of the troughs themselves 

 with coarse hay and evergreen boughs it is possible to keep them there the year 

 round; but for ordinary winter storage there is provided a system of sunken tanks 

 covered by a rough shed with a constant water supply. These tanks are molasses 

 hogsheads, securely hooped with iron, sunk nearly their entire depth into the ground, 

 each with an independent water supply and waste, the perforation for the latter being 

 near the surface. They have a capacity of from 100 gallons of water upward, and 

 will carry safely each 500 to 700 fish in their first winter, that is, just approaching the 

 age of one year. This arrangement has answered its purpose fairly well, and in a 

 very rigorous climate or where the water is very cold it is to be recommended ; but 

 since its construction it has been discovered that at Craig Brook it is not at all 

 difficult to protect the ordinary troughs in such a way as to insure their safety from 

 freezing, and their attendance through the winter is less troublesome than that of the 

 sunken tanks. 



A list of the articles employed for food at the station since its foundation, if 

 designed to include those used on an experimental as well as a practical scale, would 

 be a long one, and I will content myself with naming the following: On a practical 

 scale we have used butcher's offal, flesh of horses and other domestic animals by the 

 carcass, fresh fish, maggots; and on an experimental scale, pickled fish, fresh-water 

 mussels, mosquito larvte, miscellaneous aquatic animals of minute size. In the pro- 



