MASON: FEATURES OF EMERGING COHO SALMON FRY 



Table l. — Average lengths of sibling coho fry emerging from four simulated redds, stratified as to night 

 and day timing and direction of movement. Values in parentheses are percentages. 



redd 4, P<0.01). This is the outcome of the ten- 

 dencies for both increased emergence during 

 the day and increased size at emergence as time 

 progressed. 



Of the 584 fry that emerged from the simulated 

 redds, 14 rather small fry emerged 5 or more days 

 prior to the onset of general emergence. Twelve of 

 these fry emerged at night and went downstream. 

 They, and seven additional fry which also moved 

 downstream and were designated as cripples due 

 to truncated vertebral columns, were deleted from 

 the analyses. 



Most fry emerged when their yolk reserve was 

 reduced to less than 10% of total dry weight (Fig- 

 ure 5), average reserve being 5-7% of total dry 

 weight. The three rather high points (days 9-10) 

 for fry moving downstream represent small sam- 

 ples whose means were inflated by premature fry. 

 Yolk reserve in these samples was either less 

 than 8% or ranged between 26 and 60% for indi- 

 vidual fry. The large standard errors shown in 

 Figure 5 are all associated with mean values 

 inflated by premature fry. Yolk reserve did not 

 diminish with time, indicating that the majority 

 of fry were in a similar nutritional state at 

 emergence. Although there were no significant 

 differences in length and weight between fry 

 moving up or downstream, fry moving down- 

 stream had more yolk reserve (9.2%) than did fry 

 moving upstream (7.4%), this difference being 

 significant at the 1% level. Similarly, in 13 of 16 

 possible pairs of samples from the four redds, the 

 downstream fry contained more yolk reserve. 



To discover if fry were feeding within a short 

 time of emergence, the digestive tracts of 75 fry 

 emerging from redds 1 and 2 were examined. 

 These fry were representative with regard to 

 night or day emergence and upstream or down- 

 stream movement following emergence, through- 

 out the period of emergence. No dietary differ- 



ences were found in the 74 fry that had fed 

 shortly before their capture. As both stomach and 

 intestine contained food particles, fry emerging 

 at night probably fed that night or during the 

 preceding hours of daylight while in the redd. 

 Chironomids constituted nearly 65% of their diet 

 (Table 2), mites and Collembola made up 17%, 

 and together these three items were consumed by 

 83% of the fry. 



At time of capture in the upstream and down- 

 stream compartments, no fry had yet reached 

 neutral buoyancy although some had partially 

 filled air bladders. 



T3 



O 

 O 



50 



45 



40 • 



25 



o 20 



15 



> 



^ in 



o 



>- 



4 6 8 10 12 14 16 IB 



DAY OF EMERGENCE 



Figure 5. — Yolk reserve of coho salmon fry at emergence. 

 Solid symbols indicate downstream movement following 

 emergence; open symbols indicate upstream movement. Ver- 

 tical bars indicate ±2 SE. For the remaining points, the range 

 in SE was 0.1-1.0, and 90% ranged from 0.1 to 0.6. 



171 



