Effects of dreissenid mussels, chironomids, fishes, and zooplankton on growth of round goby in experimental aquaria

There is a widely accepted paradigm supported by early field and laboratory observations that the adult round goby (Neogobius melanostomus) is highly adapted to, and primarily survives on, dreissenid mussels. However, more recent stable isotope and diet analyses indicate that the round goby may not rely on dreissenid prey to the extent that was previously believed. We conducted a feeding experiment where round gobies were provided with an excess of one of four naturally occurring diets for 25 days - dreissenid mussels, juvenile fish, chironomids, or zooplankton. Round gobies fed dreissenids had significantly lower growth (0.04 g day ^-1) than individuals fed fish and chironomids (0.13 g day ^-1) and displayed the same weight loss as round gobies fed only zooplankton. Although dreissenids are often consumed by round gobies, this likely happens only when more profitable prey such as fish and non-dreissenid invertebrates are lacking or difficult to capture. Additionally, field observations of round goby diets that have supported the paradigm may overestimate the importance of dreissenid prey due to the longer retention time of shells in round goby guts compared to other soft-bodied prey. Our results provide direct evidence supporting recent findings that dreissenid mussels may not be as essential to round goby survival as previously considered.