Can filter‐feeding fishes improve water quality in lakes?

Abstract

1. In this paper we examine the potential of a cichlid fish species (Sarotherodon galilaeus) to both maintain positive growth rates through filter‐feeding on phytoplankton and improve water quality in Lake Kinneret through suppression of dinoflagellate (Peridinium gatunense) blooms. 2. Seasonal plankton consumption by S. galilaeus from Lake Kinneret was examined experimentally by monitoring changes in plankton assemblages during 24 h in 5‐m3 mesocosms containing varying densities of fish. Taxon‐specific grazing rates ranged from 0 to 17 mg gfish day–1, with mean total consumption of 1.6% fish body weight per day. During the spring bloom of P. gatunense, S. galilaeus consumed mostly (94%) netphytoplankton (≥20 μm). The remaining 6% consisted mostly of nanophytoplankton (<20 μm). During the summer and fall, net‐ and nanophytoplankton accounted for 54 and 42%, respectively, of the diet of S. galilaeus. Zooplankton and flagellated and ciliated protozoans made up the remaining 4%. 3. Simulations using a fish bioenergetics model indicated that consumption rates (C) were near maximum in spring (90%Cmax), while consumption was reduced in summer‐fall (59%Cmax). Sarotherodon galilaeus obtains sufficient energy through filter‐feeding year‐round, although most growth (≥60%) occurs during the spring P. gatunense bloom. 4. Despite efficient feeding on P. gatunense and nanophytoplankton by S. galilaeus, estimates of instantaneous plankton mortality caused by ingestion were two orders of magnitude lower than maximum potential plankton growth rates. Thus the potential for the S. galilaeus population in Lake Kinneret to positively affect water quality through algal suppression is low.

Effects of the Nile tilapia (Oreochromis niloticus L.) on the plankton community of a tropical reservoir during and after an algal bloom

“…Therefore, the strength of the negative effects of filter-feeding fish on their major (larger) planktonic resources was reduced when phytoplankton biomass was high during the algal bloom. This result supports the conjecture that filterfeeding fish such as adults of Nile tilapia may have less influence on zooplankton and phytoplankton dynamics in eutrophic than mesotrophic lakes and may not be able to control algal blooms (e.g., Hambright et al, 2002;Rondel et al, 2008). However, this pattern was not observed for the total zooplankton and phytoplankton biomass in our experiments, because smaller zooplankton (i.e., microzooplankton) and smaller algae (i.e., GALD \ 50 lm) were more strongly suppressed by fish during than after the algal bloom, counteracting the strength of the response of the larger zooplankton and algae.…”

“…Despite efficient feeding on phytoplankton by some tilapia species, their potential for suppressing algal blooms and improving water transparency has been considered low because estimates of instantaneous plankton mortality caused by fish ingestion is much lower than maximum potential plankton growth rates during blooms (Hambright et al, 2002). Moreover, the per capita ingestion rates of algal biomass by filterfeeding fish like Nile tilapia increases with algal biomass in a curvilinear way (i.e., type II functional response; Turker et al, 2003).…”

A Bioenergetic Analysis of Factors Limiting Brown Trout Growth in an Ozark Tailwater River

“…If the majority of prey is sub-optimal in size, poor growth rates often result (Bannon and Ringler 1986;McKinney and Speas 2001). The net energy gain realized from a prey item is most closely related to prey size and energy density (Elliott 1976;Ringler 1979;Hambright et al 2002). However, efficient use of prey energy should be considered in a specific 'environmental context'.…”

Cyanobacteria are controlled by omnivorous filter-feeding fish (Nile tilapia) in a tropical eutrophic reservoir

“…The functional response of the tilapia can be approximated to a linear function when cyanobacteria biomass is below 20 mg WW l -1 (wet weight) or 5 mg C l -1 (carbon content, assuming it is about 1/4 the wet weight) such as in our experiment (Turker et al, 2003c). Because the tilapia did not gain or lose weight during the experiment, we assumed that they had grazing rates ranging from 0.005 to 0.015 mg g fish -1 day -1 (Hambright et al, 2002), meaning that the total consumption ranged from 0.5 to 1.5% fish body weight per day. Thus, we assume that our 160 g tilapia had consumption rates ranging from 0.8 to 2.4 g per day during the experiment.…”