Effects of Herbivorous Fish on Competition and Growth of Canopy-Forming and Meadow-Forming Submerged Macrophytes: Implications for Lake Restoration

Submerged macrophytes play a pivotal role in the restoration of shallow lakes. Compared to meadow-forming Vallisneria, canopy-forming Myriophyllum spicatum exhibits characteristics that may render it the dominant species. However, M. spicatum may hamper recreational and commercial activities. Herbivorous fish may potentially regulate the biomass and interspecific competition between the two plant species. We conducted an enclosure experiment to elucidate the effects of grass carp (Ctenopharyngodon idella) and Wuchang bream (Megalobrama amblycephala) on the biomass ratio and morphological traits of M. spicatum and V. denseserrulata. Grass carp significantly reduced the biomass, density, and relative growth rate of both plant species, while Wuchang bream had no significant effect on any of these variables. Accordingly, the biomass ratio of M. spicatum to V. denseserrulata was significantly lower in the grass carp treatment than in both the fish-free controls and the Wuchang bream treatment. Wuchang bream significantly decreased the individual height of V. denseserrulata, whereas grass carp substantially reduced the height of both plant species. Our findings suggest that Wuchang bream may be more appropriate for maintaining meadow-forming species such as Vallisneria than grass carp, though it faces challenges in controlling both the biomass and height of canopy-forming species like M. spicatum.