Can round goby (Neogobius melanostomus) caught by rod and line be used for diet analysis?

Sample structure and diet of round gobies (Neogobius melanostomus) captured by angling (ANG) and electrofishing (EF) at adjacent sites in their native distribution range (Bulgarian Danube) were compared to determine whether ANG fish could be used for diet analysis. In total, 100 round gobies were captured, 52 through angling and 48 by electrofishing. EF fish were significantly smaller than ANG fish, though modal size was comparable. There was no significant difference in condition between EF and ANG. Sex ratios did not differ significantly from 1:1 in either sample. ANG fish had significantly more empty stomachs than EF fish (56% and 4%, respectively). Thirteen food items were recorded, with no significant difference in diversity between ANG and EF. Crustaceans dominated in ANG fish diet and molluscs in EF diet, though this may be an artefact of degree of stomach fullness. We suggest that angling alone is unsuitable for sampling fish for diet analysis, as it is highly selective for both fish size and degree of stomach fullness. (C) 2012 International Association for Great Lakes Research. Published by Elsevier B.V. All rights reserved.