Effects of two subtropical piscivorous fish species on sediment disturbance and water quality: Implication for restoration by stocking piscivores

Subtropical lakes are often dominated by benthi-omnivorous fish (e.g., crucian carp) that may substantially disturb sediments and thereby increase water turbidity and nutrient concentrations. Piscivores stocking is sometimes used to control these benthi-omnivores in the expectation that they will reduce their adverse effects on the water quality. However, in shallow subtropical lakes the benthic foraging activities of piscivorous fish may also disturb sediments, a topic that has not yet been well elucidated. Here, we conducted a 6-day mesocosm experiment to explore the bioturbation effects of two native subtropical piscivorous fish (i.e., snakehead, Channa argus and mandarin fish, Siniperca chuatsi) in prey fish (crucian carp, Carassius carassius) present and absent scenarios. Our results showed that in mesocosms without prey, both snakehead and mandarin fish greatly increased the concentrations of suspended solids. However, the concentrations of total, organic and inorganic suspended solids were significantly higher in the mesocosms with snakehead than in those with mandarin fish, suggesting that snakehead has higher bioturbation effects than mandarin fish. When crucian carp were present, we found that both snakehead and mandarin fish significantly reduced prey abundance, whereas piscivore stocking did not significantly decrease the suspended solids and nutrient concentrations. Our study revealed differential effects of two subtropical piscivorous fish species on sediment disturbance and water quality, and we suggest that for lake restoration with piscivores stocking, mandarin fish are a better option than snakehead fish as their predation effect was equal but the strength of sediment disturbance by mandarin fish was lower than that of snakehead.