Growth, encephalisation and brain morphology
Across all trout in the study (n  = 180), habitat and sex had small, but significant, effects on fork length: trout raised in simple habitats were larger than those raised in complex habitats (F 1,175 = 6.71, p  = 0.01), and males were larger than females (F 1,175 = 5.06,p  = 0.026). However, there were no significant diet or diet:habitat interaction effects (Table 3).
Among those subjects whose brains had been preserved for morphological analyses (n  = 78), neither sex nor rearing habitat had a significant effect on relative brain mass, but those trout raised on the high n-3 LC-PUFA diet had larger brains than those raised on the low n-3 LC-PUFA diet (F 1,77 = 9.62, p = 0.003) (Table 4; Fig. 4). Although sex had no significant effect on the relative volume of any brain region, an interaction between diet and habitat did affect olfactory bulb size (F 1,77 = 5.96, p = 0.017): in simple habitats, trout raised on low n-3 LC-PUFA had larger olfactory bulbs, while in complex habitats, it was those raised on high n-3 LC-PUFA that had the larger olfactory bulbs. No other brain region was specifically affected by diet or habitat.
Table 3. Effects of diet, habitat and sex on fork length (FL) of 180 experimental brown trout, tested with ANOVA.