Effect of Freshwater Toxic and Non Toxic Cyanobacteria , ( Microcystis Aeruginosa ) Strains on Some Biochemical Parameters of Oreochromis Niloticus

Abstract Grazing of zooplankton on phytoplankton may contribute to a reduction of harmful cyanobacteria in eutrophic waters. However, the feeding capacity and interaction between zooplankton and toxic cyanobacteria vary among grazer species. In this study, laboratory feeding experiments were designed to measure the grazing rate of the copepod Cyclops vicinus on Microcystis aeruginosa and the potential microcystin (MC) accumulation in the grazer. Copepods were fed a mixed diet of the edible green alga Ankistrodesmus falcatus and toxic M. aeruginosa for 10 days. The results showed that C. vicinus efficiently ingested toxic Microcystis cells with high grazing rates, varying during the feeding period (68.9–606.3 Microcystis cells animal-1 d-1) along with Microcystis cell density. Microcystis cells exhibited a remarkable induction in MC production under grazing conditions with concentrations 1.67–12.5 times higher than those in control cultures. Furthermore, C. vicinus was found to accumulate MCs in its body with concentrations increasing during the experiment (0.05–3.21 μg MC animal-1). Further in situ studies are needed to investigate the ability of Cyclops and other copepods to assimilate and detoxify MCs at environmentally relevant concentrations before deciding on the biocontrol of Microcystis blooms by copepods.

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Demographic responses of selected rotifers (Rotifera) and cladocerans (Cladocera) fed toxic Microcystis aeruginosa (Cyanobacteria)

Fundamental and Applied Limnology / Archiv für Hydrobiologie ◽

10.1127/fal/2020/1285 ◽

2020 ◽

Vol 193 (3) ◽

pp. 261-274

Author(s):

Alfredo Pérez-Morales ◽

S.S.S. Sarma ◽

S. Nandini ◽

Cristian Alberto Espinosa-Rodríguez ◽

Ligia Rivera-De la Parra

Keyword(s):

Population Growth ◽

Life Table ◽

Microcystis Aeruginosa ◽

Green Algae ◽

Somatic Growth ◽

Phytoplankton Species ◽

Scenedesmus Acutus ◽

Cladoceran Species ◽

Toxic Cyanobacteria ◽

Demographic Responses

Tropical waterbodies contain several species of toxic cyanobacteria including Microcystis, which adversely affect the somatic growth, survival and fecundity of zooplankton. Scenedesmus, one of the most common green algae, is even found in Microcystis -dominated waterbodies. It is, therefore possible that in natural ponds, rotifers and cladocerans feed on mixed phytoplankton species containing algae and cyanobacteria. In this work, we quantified demographic responses of three rotifer species (Brachionus calyciflorus, B. rubens, and Plationus patulus), and three cladoceran species (Simocephalus mixtus, Daphnia cf. mendotae and Moina macrocopa) fed toxic Microcystis aeruginosa only or mixed with Scenedesmus acutus. The highest population growth for both rotifer and cladoceran species was observed when Scenedesmus was offered alone or at 75 % of the diet. Daphnia cf. mendotae and B. rubens were less affected by Microcystis while M. macrocopa and B. calyciflorus were more adversely influenced, which was also corroborated by life table demography. In competition bioassays, D. cf. mendotae was more efficient, alone or in competition, when fed with 50 or 25 % of Microcystis. This work explains the dynamics of the zooplanktonic community against gradual changes in phytoplankton due to the presence of cyanobacteria.

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