Fatty acid analyses
There were significant differences in DHA routing to various tissue/lipid types (F 3,114 = 239.6,R 2adj = 0.86,p  < 0.001), with brain PL receiving the highest percentage (post hoc : brain PL compared to each other type, allp  < 0.001) and muscle PL having a higher percentage than NL in either brain or muscle (post hoc : bothp  < 0.001) (Fig. 6A). For individual tissue/lipid types, however, there were differences in DHA content between diet groups (Pillai = 0.97, F 1,25 = 153.3,p  < 0.001) and habitats (Pillai = 0.38,F 1,25 = 3.34, p  = 0.027). Trout on the low n-3 LC-PUFA diet had lower DHA percentages than trout on the high n-3 LC-PUFA diet in muscle PL (F 1,25 = 10.0,p  = 0.004) and muscle NL (F 1,25 = 460.0,p  < 0.001), although there was no significant difference in brain lipids. Trout raised in complex habitats had higher DHA percentage in muscle NL (F 1,25 = 13.3,p  = 0.001), habitat had no significant effect on routing DHA to other tissue/lipid types (Fig. 6A).
Depletion of ∆δ 2HDHA indicated there was considerable biosynthesis amongst trout fed the low n-3 LC-PUFA diet (Pillai = 0.95, F 1,21 = 80.6,p  < 0.001), despite lower DHA content. The effect of diet on ∆δ 2HDHA depletion was highly significant (all p  < 0.001) for all tissue/lipid types (Fig. 6B). Neither habitat nor sex exerted a significant effect on ∆δ 2HDHA depletion.
Because content and depletion of ∆δ 2H in the n‑6 LC-PUFA, ARA 20:4n‑6, are related to n‑3 LC-PUFA biosynthetic activity, it is important to consider these when investigating effects on DHA (Sprecher, 2000). ARA content across tissue/lipid types was affected by diet (Pillai = 0.73, F 1,23 = 13.52,p  < 0.001), but not habitat or sex. Trout raised on the low n-3 LC-PUFA diet had significantly higher percentages of ARA than the trout raised on high n-3 LC-PUFA in each tissue/lipid type (from brain NL, F 1,23 = 6.06, p  = 0.023 to brain PL, F 1,23 = 36.08, p  < 0.001) (Fig. 6C). This was reflected in greater biosynthesis among the low n-3 LC-PUFA-fed trout than the high n-3 LC-PUFA-fed trout, seen in the greater depletion of Δδ 2HARA in brain PL (F 1,18 = 5.49, p  = 0.031) and muscle NL (F 1,25 = 23.45,p  < 0.001). Trout from simple habitats also showed greater biosynthesis of ARA than trout from complex habitats in muscle NL (F 1,25 = 6.02, p  = 0.021) (Fig. 6D).