An investigation was undertaken to establish if Gammarus pulex and Asellus aquaticus preferred a diet of unconditioned, artificially or naturally conditioned alder leaves (Alnus glutinosa). Standardised, 24 hour ex situ feeding assays were undertaken with both species to determine their food preference. The results showed that A. aquaticus ate more leaf material compared to G. pulex (Z 23.909, P 0.001) when exposed to all three test variables. Also, both G. pulex and A. aquaticus demonstrated a preference for naturally conditioned leaves compared to the other two variables, with unconditioned leaves proving the least popular food option for both macroinvertebrates (Z 18.803, 𝑃<0.001). However, both species ate varying amounts of all the leaf treatments (Z 136.399, 𝑃<0.001). Subsequently, the author outlined a feeding methodology for natural alder leaf conditioning that could be used during a laboratory breeding programme.