Abstract
The presence of omnivorous fish is known to affect aquatic ecosystems, including water quality. The effect, however, depends on the species in question, and our knowledge is limited on the effect of omnivorous crucian carp (Carassius auratus), a common and often the most numerous fish species in eutrophic shallow lakes in China. We conducted a 70-day outdoor experiment in mesocosms with and without crucian carp to examine whether this species adversely affects water quality by increasing the levels of total nitrogen (TN) and total phosphorus (TP), thereby stimulating the biomass of phytoplankton and increasing water turbidity. Compared with carp-free controls, the presence of crucian carp resulted in higher TN and TP in the water column, greater phytoplankton biomass and lower periphyton biomass, measured as chlorophyll a. Total suspended solids (TSS) also increased in the presence of fish. We conclude that crucian carp can increase TN and TP, enhance phytoplankton biomass, and increase water turbidity, thereby contributing significantly to the deterioration of the water quality. In addition to controlling external nutrient loading, the removal of crucian carp may help to improve water quality in warm shallow eutrophic lakes.
Highlights
Fish are major consumers in many aquatic ecosystems and can have large effects on aquatic ecosystems, including effects on community structure and trophic state [1,2]
total nitrogen (TN) and total phosphorus (TP) were higher in the crucian carp treatments than in the controls on every sampling occasion except day 56 and day 70
We found an increase in Total suspended solids (TSS) and a reduction in the light intensity on the sediment surface linked with the presence of crucian carp
Summary
Fish are major consumers in many aquatic ecosystems and can have large effects on aquatic ecosystems, including effects on community structure and trophic state [1,2]. A significant body of research has demonstrated a variety of ways in which omnivorous fish influence shallow lake systems by modifying nutrient levels and turbidity, boosting the growth of phytoplankton and suppressing zooplankton. The disturbance of sediments associated with benthic feeding of omnivorous fish may increase the turbidity of water [8,9] and facilitate the release of nutrients in shallow lakes [10,11,12]. Excretion by omnivorous fish can increase nutrient concentrations and stimulate phytoplankton growth [3,9], which leads to reduced light intensity at the sediment surface [14,15,16]. Omnivorous fish can influence the community structure of zooplankton [19,20] that play a key role in the environmental state of lakes by grazing on phytoplankton [21]
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