|
SPAWNING
Seasons
Wild Rainbow generally spawn in the spring, usually February through June, but there are exceptions. Some strains of domesticated Rainbow in hatcheries have been bred to spawn in the fall, so that their offspring will be larger at planting time.
Location
The place of spawning for Rainbow is in streams, usually the smaller, swifter streams of clear, cool, unpolluted water. The male and female meet at some point in the stream where the size and depth of the gravel are satisfactory. The gradient of the stream bed and the depth and velocity of the water must meet certain requirements, for it is necessary that the flow of water through the gravel be sufficient to keep the eggs well oxygenated and free of smothering silt.
Once the pair of spawners has found the gravel bed which fulfills all of their requirements, the female proceeds to dig a pocket, into which she will deposit her eggs. With strong flips of her tail, she throws aside the gravel until a depression has been formed. A large steelhead Rainbow weighing 10 pounds may dig a pocket measuring two feet long, a foot wide, and 10 inches deep, while small “resident” Rainbow of the mountain brooks will dig much smaller pockets corresponding to their size.
Egg Laying & Fertilization
Once the pocket has been completed, the female, with rapid, vibratory contractions of her body muscles, expels a part of her ripe eggs and as they spurt forth the male ejects a stream of white milt into the gravel pocket with the eggs. Even though the water flows swiftly over the depression, the back eddy formed within the pocket holds the eggs and the sperm together until the female can cover them with loose gravel. In the meantime, the soft eggs are absorbing water and soon become perfectly round. Within the first few seconds after spawning, one of the many thousands of spermatozoa released by the male fish has entered the egg through a minute opening called the micropyle and fertilization is completed.
Into the first gravel pocket the female and the male have put only a part of their eggs and milt. She must dig more such pockets into which more eggs are laid and fertilized. Normally, these pockets are dug one upstream from the other, so that in forming the second depression the gravel is washed down and helps cover the first pocket formed. The completed series of covered pockets is called a redd.
The size and number of trout eggs vary in more or less direct relation to the size of the female. A six-inch trout of a small tributary stream will lay 200 or 300 small, amber-colored eggs, while a large steelhead may produce 6,000 or more.
The egg
After trout eggs have been deposited and fertilized, they are usually covered with gravel. Any developing egg must have oxygen and it is essential, therefore, that trout eggs be kept free of silt and be continually bathed by fresh, well aerated water. Most types of pollution are harmful and sometimes lethal to developing trout eggs.
|
 |
The length of time required for a trout egg to hatch largely depends upon the water temperature. Rainbow eggs will hatch in 80 days when the water averages 40 degrees Fahrenheit. If the temperature were 55 degrees, they would hatch in 24 days. Those eggs which are laid in the fall, when the water is cold, nearly always remain in the gravel all winter and hatch in the spring or early summer when temperatures increase.
At hatching time the egg shell breaks open and the little fish emerges carrying its sac of yolk and for several weeks that is all the food it has to live on. When the yolk has been absorbed, the fry work their way up through the gravel and start to look about for tiny aquatic animals to eat.
The Fingerling
Now that the young trout is on its own and can no longer depend upon yolk for food, it becomes known as a “fingerling” and this is the name applied until it is a year old when, quite naturally, it is called a yearling.
Trout, both small and large, eat a great variety of foods. Now and then, bits of plant material can be found in their stomachs, but ordinarily they are carnivorous. Insects of one kind or another are the preferred foods after the fish are large enough to eat them. It is quite correct to say that trout will eat almost anything, including other fingerlings, but insects are the “bread and butter” of their diet.
As the young trout eats, it grows; but the speed of its growth may vary from three inches or less to over a foot a year. It is difficult to tell how old a trout is by its size, because there are many factors which influence the rate of growth.
The amount a trout eats can vary widely and depends largely upon the amount of food available, the temperature of the water, and the size of the body of water it is living in. As an example, a “resident” Rainbow which spends all its life in a small pool in a cold, mountain brook will not eat as much food in an entire year as its Steelhead cousin may eat in a week. Naturally, its growth will be very slow. It may be 3 inches long by the end of its first year and perhaps only five inches long by the time it is two years old. Its cousin, who has gone to the ocean at about the end of its first year, may grow to be 16 inches long and reach a weight of 1 pound in the time it has taken the stream Rainbow to grow to five inches.
There are a few large lakes in the world in which Rainbow reach a weight of 16 pounds in four years. In many cases where growth is very rapid we find the trout eating smaller fish almost exclusively and the water temperature remaining somewhere in the neighborhood of 60 to 65 degrees Fahrenheit. In colder water the appetite of trout diminishes.
The Adult
Fish, unlike birds and mammals, never entirely stop growing.
Most trout die from one cause or another long before they reach their maximum life span and only the exceptional fish will attain a large size.
Certainly only “one in a million” trout will reach the maximum age for any particular species and it is difficult to say how old trout might live to be if a violent death or some disease did not intervene.
PREVIOUS - THE TROUT FAMILY
Sources for our info on Trout:
Article on Ranbows and Steelhead at www.bcadventure.com
Article on Kamloops Trout at www.bc adventure.com
California Department of Fish and Game
U.S. Dept. of the Interior, USGS
|
