Biological control of Volvox sp. bloom in fish rearing ponds

Document Type : Original Article

Authors

1 International Sturgeon Research Institute

2 Associate professor-International sturgeon research institute

3 Guilan Fisheries,Anzali,Iran

4 ShahidDr.Beheshti Sturgeon Restoration and Genetic Coservation Center

Abstract

Among algae groups, green algae are the most important group to create bloom in fish rearing ponds. In this study, in this study rice straw powder was used to control the bloom of a green algae (Volvox sp.) in sturgeon rearing ponds. To evaluate the quantity and quality of water in the rearing ponds, the factors such as temperature, oxygen, pH, nitrate, phosphate, ammonium, type and amount of phytoplanktonic and zooplanktonic cells were measured weekly throughout the study period. To control the algae bloom 90 kg/ha rice straw powder was used. The objectives of addition of rice straw powder was preventing phytoplankton cell growth and developing competition for nutrient and improvement of zooplankton biomass in the ponds.
A total of 15 genera of 4 phyla of Cladocera, Copepoda, Protozoa and Rotifera from zooplankton and 11 genera from 3 phyla of Bacillariophyta, Chlorophyta and Cyanophyta from phytoplactones were identified. Cladocera and Chlorophyta showed the highest percentages zooplankton and phytoplankton in all rearing ponds respectively.The pH and dissolved oxygen content of the treatment ponds were significantly different with the control ponds (P <0.05). The amount of ammonium did not vary significantly among treatment and control ponds. The abundance of Daphnia spp. and zooplankton was significantly different in treatment and control ponds (P <0.05). The abundance of Volvox sp. colonies in treatment ponds dropped down to zero in a few days which confirmed the positive effect of rice straw powder addition in reducing the population of Volvox sp. Since the fish harvested from the treatment and control ponds showed significant differences in their mean weight, it is concluded that control of algal bloom resulted in appropriate feeding and enhanced weight gain, however the treatment and control ponds did not vary significantly in terns of number of harvested fish.

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