STUDIES ON REPORODUCTION OF RAINBOW TROUT, SALMO GAIRDNERI, WITH SPECIAL REFERENCE TO EGG TAKING-III
ACCELERATON OF SPAWNING BY CONTROL OF LIGHT
1962 Volume 28 Issue 11 Pages 1070-1076
Details
1962 Volume 28 Issue 11 Pages 1070-1076
An experiment was made to induce the earlier spawning of raindow trowt by the control of photoperiodicity artificially.
The light schedules and results obtained were as follows;
1) The Experiment No. 1 was conducted in a circular pond (diameter 5.3 m.) supplied with a constant flow of spring water at the rate of about 200 liters per minute and the temperature was constantly kept at nearly 10.6°C. The light schedule is shown in Fig. 1. It was controlled by 4 overhead 100 watt-lamps and a dark curtain covering over the pond. 30 females and 20 males were used.
The Experiment began on March 18, 1957. Egg taking operation was permitted to start on October 12, 1957, and 30, 164 eggs were collected from 13 females (43 % of fish used) by December 12 (Table 2). Only 5.6 percent of the control fish spawned by that time.
2) The light schedule of the Expetiment No. 2 is shown in Fig. 2. Use was made of the same pond and equipments as in the Experiment No. 1. 40 females and 20 males of 2-and 3-year-old rainbow trout were stripped on January 21, 1958, and transfered to the ex-perimental circular pond on the same date, but they reduced in number to 28 females and 15 males by the beginning of the experiment.
The experiment began on February 23, 1958, The first eggs were taken from a female on August 20, 1958, and by December 15, 21 females (75 %o of fish used) produced 41, 048 eggs (Table 3). Therefore, it was confirmed that these fish spawned two times (January and August to December) in 1958 by the experiment. Since the egg taking from 75 percent of the control fish lasted to January 18, 1959, it was apparent that the fish experimented spawned a month earlier than the control fish.
3) In Experiment No. 3, both rainbow trout (29 females, 15 males) and brook trout (12 females, 9 males) were used (Table 1). Experimental pond and equipments were same as in those of Experiment No. 2, except the use of 200 watt- instead of 100 watt-lamps. The fish recieved 6 hours of artificial light (lighting during 9 a. m. -3 p. m.) per day through the experiment from July 10 to December 29, 1961.
In brook trout, the first eggs were taken from a female fertilized by 4 males riped on October 2, 1961, and by November 11 nearly 36, 000 eggs were collected from all 12 females (Table 4). The control fish numbering only 38.9 percent spawned by that time.
In rainbow trout, egg taking operation was permitted to start on October 31, and about 55, 000 eggs were collected from 26 females (89.6 % of fish used) by December 29 (Table 4). Only 59.9 percent of the control fish spawned by that time (Fig. 3).
4) Number of eggs taken per female, weight of egg, and percentage of eyed eggs obtained both on control and experimented fishes are shown in Table 5. Egg size of tested fish was slightly smaller than that of the control, but the number of eggs taken per female being reversed.
It is worth noticing that the period of light control in Experiment No. 3 was over 100 days shorter than in the other two experiments, but it still has similar effect as in Experiments Nos. 1 and 2. Between the two species tested brook trout appear to be more readily adjusted to light control than rainbow.
