Effect of dietary fatty acids and ration size on alewife growth and condition score

Accurately forecasting alewife condition and growth remains a high priority in Great Lakes fisheries management.  In this study we examined how source of dietary fatty acids and daily ration influenced alewife growth and condition.  Alewives received isocaloric diets with either flax-olive oil mix (low EPA-DHA fatty acids) or fish oil (high EPA- DHA) containing diets. Alewives were fed either 1% or 3% of their wet body weight per day.  After eight weeks, alewives fed 3% fish oil diet (25.0 ± 0.53 g) were larger (P<0.05) than those maintained on 3% flax-olive oil diet (22.6 ± 0.52 g).  Condition (Fulton’s K) was higher in fish fed 3% fish oil (0.89 ± 0.006) compared to alewives fed 1% plant oil (0.71 ± 0.010). The current Wisconsin alewife bioenergetics model could not account for these differences in growth.  Our results suggest that food web changes in fatty acids may reduce alewife growth rates, and these results are similar to a previous study using corn oil. Incorporating food quality into alewife growth models is warranted to improve the accuracy of their predictions.