FISHERY BULLETIN: VOL, 69. NO. 3 



Adverse effects of low temperatures during- 

 certain stages of development were also ob- 

 served for other fishes. KinneandKinne (1962) 

 exposed embryos of the cyprinodont Cyprinodon 

 maculavis to different temperature-salinity-oxy- 

 gen combinations and found a period of "low 

 thermal stability," which we presume to mean 

 low resistance, in embryos exposed to critically 

 low tem])eratures during early development 

 (fertilization to gastrulation) . Stockard ( 1921 ) 

 conducted a number of experiments with eggs 

 of the cyprinodont Fundulus heteroclitus which 

 he placed in a refrigerator at 5°, 7°, and 9° C 

 for various lengths of time and at various stages 

 of development. Development was almost, if 

 not completely, stopped at 5° C and greatly 

 slowed at 9° C. Exposure to 5° C just after gas- 

 trulation commenced was not noticeably injur- 

 ious, but exposure to low temperatures during 

 earlier stages resulted in increased mortalities 

 and gross anomalies among survivors. 



Piavis (1961) incubated sea lamprey eggs at 

 various constant temperatures and learned that 

 viable burrowing larvae could be produced at 

 15.6° C but not at 12.8° C. McCauley (1963) 

 also explored the lethal temperature limits of 

 embryonic sea lamprey. He found that the nar- 

 row range of constant temperature, 15.0° to 

 25.0° C, necessary for successful hatching may 

 be extended to 12.2° to 25.6° C if gastrulation 

 is completed before the eggs encounter temper- 

 atui'e extremes. 



The work of Taning (1952) on the effects of 

 temperature on the development of Sahno trntta 

 trutta supports Stockard's conclusion that the 

 earlier the stage of development is arrested, the 

 moi'e severe will be the effect. 



The lowering of temperatures in Grace Creek 

 by the proposed hydroelectric plant would be 

 greatest just before and during gastrulation of 

 the pink salmon embryos (Figure 1). 



EXPERIMENTS IN LABORATORY ON 

 PINK SALMON 



We conducted an experiment in the laboratory 

 to determine if iiink salmon eggs could survive 

 and develop normally under the projected ther- 

 mal regime for Grace Creek. The eggs for the 



study came from two pink salmon collected Sep- 

 tember 7, 1966, from Grace Creek. The eggs 

 were thoroughly mixed and fertilized by sperm 

 from two males in the field. 



Embryonic development had begun before 

 the eggs were placed in the experimental array 

 because the temperature in the transporting 

 container ranged from 7° to 12° C (average, 

 10.8° C) during the 10-hr trip to the laboratory. 

 According to Soin (1954) the first cleavage di- 

 vision occurs in pink salmon eggs about 7 hr 

 after fertilization at 11° C. Knight (1963) 

 showed that about 2.5 hr elapse between suc- 

 cessive cleavage divisions in rainbow trout eggs 

 at 12.2° C. Therefore, we estimate, but did not 

 confirm, that the Grace Creek pink salmon eggs 

 completed two cleavage divisions before they 

 were transferred to the controlled temperatures 

 of the experiment. 



The eggs were incubated in 55- and 42.5-mm 

 diameter Buchner funnels with perforated 

 plates. Each of the large funnels was stocked 

 with 120 eggs and each of the small ones with 

 25 eggs. The water M'as introduced through the 

 stem of the funnel to produce an upwelling flow 

 through the plates that supported the eggs. The 

 water was not recirculated, and flow rates' were 

 set to deliver an apparent velocity of about 200 

 cm hr to the eggs. Dissolved oxygen content 

 of the water as it entered the funnels was above 

 8 ppm at all times. 



The experiment involved 16 treatments con- 

 sisting of four initial incubation temperatures 

 each with four exposure periods. The four tem- 

 peratures were ambient," 4.5°, 3.0°, and 2.0° C; 

 and the four exposure periods were 15, 27, 37, 

 and 103 days. All of the exposure periods be- 

 gan 10 hr after fertilization on September 7, 

 1966. When the experimental cold treatment 

 for each lot was completed, the eggs were trans- 

 ferred to ambient temperature to complete their 

 incubation. Temperatures were recorded con- 

 tinuously; the daily means (Figure 3) were 

 usually within ±0.5° C of the planned levels. In- 



' Apparent velocity was obtained by dividing the rate 

 of flow to the egg container in cubic centimeters per hour 

 by the cross-sectional area of the container in square 

 centimeters. 



° Ambient temperature is the unmodified temperature 

 of the laboratory water supply. See Figure 3. 



590 



