84 



THE GROWTH AND VARIATION OF FISH. 



How can yoit tell the age of a fish? 

 This question is often asked and just so 

 often is the answer unsatisfactory. 



A fish is a cold-blooded animal ; that is, 

 his temperature is nearly the same as 

 that of the water in which he lives. His 

 circulation is sluggish and his appetite is 

 a variable quantity. He has the capacity 

 to take in large quantities of food at one 

 meal and properly assimilate it; on the 

 other hand he is able to fast for weeks at 

 a time. He has his own notions about 

 eating, and it is quite impossible to in- 

 duce him to change them, and all this has 

 considerable influence on his rate of 

 growth. It is out of the question to ex- 

 pect him to grow when he is fasting ; on 

 the other hand he must draw on the fat 

 he has stored up in his body to furnish 

 him energy for his muscular movements 

 and to carry on the ordinary functions of 

 nutrition. The fish here has an advant- 

 age over the warm-blooded animals, for 

 he does not need to generate heat to keep 

 his body at a constant temperature. The 

 amount of food often eaten at one time is 

 quite remarkable. I remember once of 

 taking nearly one pound of sunfish from 

 the stomach of a Large-mouthed Black 

 Bass. This does not indicate that a bass 

 must eat such meals three times each day, 

 it only shows his capacity to make use of 

 a large quantity of food when it is abund- 

 ant and his stomach feels the need of it. 

 A trout is a good feeder ; his stomach 

 and mouth are large, much in size like 

 that of the black bass. From experi- 

 ments conducted at Neosho, Missouri, by 

 Mr. Page, he found that a young trout 

 did best on a daily ration of solid food 

 equal to about seventy-five per cent 

 of its weight. On this amount the 

 trout would reach an average length 

 of six inches in one year. The av- 

 erage amount of solid food con- 

 sumed daily by a man is from one and 

 one-half to two per cent of his weight, or 

 more than twice that consumed by our 

 active, growing young trout. As men- 

 tioned before, the trout is relieved from 

 generating heat to keep his body at a con- 



stant temperature, and at one usually 

 much higher than the medium in which 

 he lives. 



As an example of the ability of fishes 

 to go for some time without eating, we 

 need only mention our Pacific salmon. 

 There are five species of these large fishes 

 on the Pacific coast. In the early spring 

 (April) many of the largest species, the 

 Chinook, start up the Columbia river for 

 the purpose of spawning. They reach 

 the headwaters of the Columbia in Idaho 

 early in September. During this journey 

 they eat nothing. We know they do not 

 eat, for of the thousands caught each 

 year for the canneries none are found 

 with food in their stomachs ; besides, this 

 organ has become much shrunken. If 

 they did eat on this journey there would 

 not, I believe, be enough animal and plant 

 life in the Columbia to furnish each sal- 

 mon with more than one meal. Now 

 many of them make the journey against a 

 strong current for more than one thou- 

 sand miles, and reach an elevation of 

 about eight thousand feet above the sea. 

 When they leave the ocean they are in ex- 

 cellent condition, by the time they have 

 reached their journey's end they are thin 

 and haggard, their vitality is so reduced 

 that soon after spawning they die — liter- 

 ally die of starvation. Their eggs hatch 

 during the winter. By the next winter 

 the young salmon are from four to five 

 inches in length, and by the following fall 

 or early winter they go to the sea, having 

 reached an average length of about ten 

 inches. After leaving the fresh water, 

 which only afforded them a scant subsist- 

 ence for nearly two years, the generous 

 ocean gives them plenty of sea room and 

 an abundance of food, which in a few 

 years prepares them to repeat the long 

 journey of their parents. We are, in case 

 of most fishes, ignorant of their life his- 

 tories, as we are of the salmon's. We 

 know the average rate of growth of the 

 salmon for the first two years, but we 

 know nothing more of them until they 

 return to fresh water to spawn. 



I mentioned that trout in the Neosho- 



