NATURAL HISTORY OF THE QUINNAT SALMON. 
81 
growth. Clay or other dirt free from organic matter is often mixed in the water to 
destroy a growth of fungus on fry. 
While carrying on the experiments at Pacific Grove in January, 1899, when 
they were 38 days old the fry Avere attacked by a very serious growth of slime, some- 
times called gill-fungus by fish-culturists. This slime was composed mostly of a 
microscopic unicellular animal with a silicious shell, belonging to the order Flagel- 
lates. Some other microscopic animals and unicellular plants, such as diatoms, were 
present. The slime collected on the gills of the fish and killed about two-thirds of 
them. They Avere treated with a 25 per cent mixture of sea Avater, which Avas very 
effective. Those which had been removed to a mixture of sea water before the 
appearance of the slime were not affected at all. 
It must not be supposed from the statements given above that hatching troughs 
and baskets must never be touched during the critical period, nor that fungus is 
the only disease to which salmon ova and the alevins are liable. As has been 
stated above, I am not giving a general method of fish-culture, but an account of 
certain investigations. If the deposits of sediment on the eggs and troughs show 
traces of decaying organic matter, especially if there is a growth of slime on the 
Sides of the trough, everything must be cleaned immediately. There is no doubt 
that microscopic plants and animals, such as bacteria and those mentioned above 
as having injured the fry at Pacific Grove, are very injurious to the eggs, alevins, 
and fi*y and must be scrupulously guarded against. 
THE ALEVIN. 
UNDER NATURAL CONDITIONS. 
The eggs that are not destroyed in one way or another when deposited by the 
spaAvning fishes lie among the rocks, where they lodge and hatch in from 6 to 9 
Aveeks, the time depending on the temperature of the water. The alevins also 
remain among the rocks at the bottom for a few weeks, and their movements, slight 
though they are, expose them greatly to such fishes as the sculpin and trout. Dur- 
ing this time the yolk supplies them with what nourishment they need, but about 
four weeks after hatching the quantity of yolk has become so small that it is not 
absorbed rapidly enough by the blood to meet the needs of growth. At this time 
also the alevin is able to swim a little, and it frequently leaves the bottom to snap 
at some floating object. Its movements are necessarily awkward on account of the 
unabsorbed yolk, and it therefore attracts predaceous fishes. This is the most 
critical period in the life of the salmon after hatching. The yolk-sac disappears 
entirely at the age of 5 or (i Aveeks, when the young are known as fry. This is the 
age at which they begin feeding. 
OBSERVATIONS ON ALEVINS ARTIFICIALLY REARED. 
General account . — In December, 1896, 855,000 eyed eggs were shipped from 
Battle Creek hatchery to Bear Valley hatchery in Marin County. Here they AA r ere 
hatched early in February, 1897, under the care of Mr. Frank Shebley, of the Cali- 
fornia Fish Commission. After the yolk-sac Avas absorbed, which was about 35 
dgys later, they were fed for a feAv days on curds of milk, and then, in the second 
week of March, Avere turned into Paper-mill Creek and its tributaries, Nicasio, 
F. C. B. 1902—6 
