240 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
Rate of groivth . — The average growth, under favorable circumstances, is about as 
follows: Oue year old, from to 1 ouuce; two years old, from 8 to 10 ouuces; three 
years old, from 1 to 2 pounds; four years old, from 2 to 3 pounds. They grow until 
they are 8 or 10 years old, but the rate of growth diminishes with age. Some will 
grow much faster than others under any circumstances, but it may be truly said that 
the rate of growth is a question of food and tenqierature of water. In water at 00° 
and with plenty of food, fish one or two years old will double their size several times iu 
a single season ; while iu water at 40° and with food limited, the rate of growth would 
probably be less than 100 per cent iu the same time. 
Temperature of ivater. — Mr. Livingston Stone says of brook trout: 
Under tbis head it may he suggested that the (|uautity and force of current and vigor of the 
water have much to do with the degree of temperature at which trout will live. For instance, when 
water does not possess much vigor, is deficient iu cprantity, and sluggisli, it will not support trout iu 
so high a temperature as when it is vigorous, plentiful, and rapid. I think it is safe to say that 
sluggish Hat water at 70^ is dangerous, if not fatal, to trout, while they will live iu vigorous, rapid 
water which occasionally runs to 80'^. I have found 85° to he fatal to them iu all kinds of water. 
(Domesticated Trout, pages 13 and 14.) 
The above will apply, iu the main, to rainbow trout also; rainbow trout will live, 
however, m warmer water than brook trout; they will thrive in ‘‘vigorous’’ water at 
85°, especially where there is some shade; in pouds I would consider that temperature 
dangerous, even with shade and a fairly good current. 
Edible qualities . — The trouts are generally recognized as being the best of all 
lian fish; but, as regards their relative value iu this respect, there is diSereuce of 
opinion. Iu comparing the rainbow trout with the brook trout (SalveUmts fonthialis), 
I find that confiicting reports come from all sections; even iu the same locality I 
find much difference of opinion, so it may be said that it is all a matter of individual 
taste. Some regard the brook trout as having the finer flavor; others think that 
the rainbows are deserving of that distinction, while still others think there is no 
difference iu the flavor of the two species. 
(rrwHnes.^.— The rainbows are ((uite game; they are active biters, and make a 
strong fight for their liberty. 
Spaioning ponds. — The construction of the spawning-ponds, with reference to their 
shape and size, is of vast importance to the trout-culturist. I regard the best size 
for these ponds about 15 by 50 feet, and from 3 to 3| feet deep, constructed entirely of 
wood and shaped as shown in plate 80. A pond shaped in this 'way gives the best pos- 
sible water circulation iu all its parts, and there are no corners for the excrement and 
other foul matter to lodge iu. The bottom of the pond should be built with a gradual 
elevation toward the upper end of about 2 inches in the length of the pond. This 
makes the i)ond practically self-cleaning; nearly all the foul matter will Avork through, 
and Avhat is left iu it can be easily gotten rid of by di'awing the Avater down low, and 
letting the fish work it out. This saA^es handling the fish, AAdiich is very important, 
especially when it is near their spawning time. 
Guard racl'. — This should be put in on an incline of about 45 degrees and made of 
thin narrow slats, as shown at C (plate 80). If the Avater is to be used over again in pouds 
beloAv, a receiver should be built underneath the bottom of the pond at the lower end, 
between the foot of the guard-rack and the dam-boards. The floor of the pond 
immediately over this receiver is to be cut away and a grating set in. This will allow 
matter to lall through into the receiA^er and from there be Avashed out through the 
