Kalish- Otolith microchemJstry to distinguish salmonid progeny 



661 



stock progeny (unpaired one-tailed t-test, /= 12.69, 

 P<0.0001). One-way analysis of variance showed that 

 there were no significant differences in mean otoHth 

 primordia Sr/Ca ratios among individuals from either 

 seawater (F=0.88, P = 0.476) or freshwater brood- 

 stock (F = 1.29, P = 0.279). Differences in otolith pri- 

 mordia composition between sea-farmed progeny and 

 freshwater progeny were not significant for Na/Ca (un- 

 paired two-tailed f -tests, t = 1.82, P = 0.076) and S/Ca 

 (^ = 0.58, P = 0.568), but were significant for K/Ca 

 ratios (/ = 3.88, P = 0.0004). Similar results were ob- 

 tained for measurements made in lapilli primordia from 

 five freshwater and five marine progeny. Table 2 also 

 presents the results of comparisons between the com- 

 position of the nucleus and post-yolk absorption regions 

 of the otoliths. 



A histogram of the frequency distribution of Sr/Ca 

 ratios determined for five primordia in the sagittae of 

 20 progeny of sea-farmed rainbow trout and 20 prog- 

 eny of freshwater rainbow trout shows that there is 

 little overlap between individual measurements from 

 the two groups (Fig. 2). Only 5% of the measurements 

 from the sea-farmed progeny overlap with 13% of the 

 freshwater progeny measurements. A frequency histo- 

 gram of the mean Sr/Ca ratios obtained from each 

 sagitta nucleus shows that the sea-farmed and fresh- 

 water progeny are clearly separated on the basis of 

 otolith primordia Sr/Ca ratios (Fig. 2). 



S Sea-farm progeny 

  Freshwater progeny 



JL 



DD 



. n , o i 



JX- 



(12 0,7 1 : 17 : ; ; ? ; ; 17 4.2 4.7 5.; 

 Otolilh Sr/Ca X 10 ' 



Figure 2 



(Aliove) F'requency distribution of i)idividual otolith Sr/Ca measure- 

 ments made in the primordia of 20 sagittae from Ovrorhi/vcliita 

 iiiykiss fry of sea-farmed Ijroodstoek and 20 sagittae from fry of 

 freshwater broodstock {N = 200), and (below) frequency distribution 

 of mean otolith Sr/Ca ratios from the same 40 sagittae. 



