Effect of Microcystis aeruginosa blooming on the production of Nile tilapia (Oreochromis niloticus) in fish ponds

Reasons for low fish farm production at Eltel El-kabeer area, Ismailia Governorate were unknown.  At the concerned area, fish survival rates have been dropped to reach less than 10% for several consecutive years.  Some of the conducted studies, concerning the high mortality rates in the concerned area, claimed that that phenomenon was initially referred to cyanobacterium blooming (Microcystis aeruginosa) thought to be ingested by fish during feeding, or assimilated through gills during breathing.  Twelve earthen ponds (each of 2000 m2 area, 100-120 cm water depth, fertilized by 125 kg chicken manure / pond / week for a period of 16 weeks, and stocked with 5000 Nile tilapia fry with a weight ranged 5-7 gm) were used in the study and were divided equally into two studied groups.  The first pond group was full of   Microcystis aeruginosa bloom, while the second pond group was free of Microcystis aeruginosa bloom.  Fish were stocked in the two previously mentioned studied pond groups, fed on feeding rate at 3 % of live body weight.  Commercial floating fish diet with 25% protein content was used in fish feeding.  Physicochemical parameters, plankton population, fish survival, fish production, and toxicity test for different fish size (5, 20, 50, 150 grams).  In addition, Artemia also were studied.   There was a significant difference between the two studied pond groups concerning all physical and chemical water characteristics investigated.  Those investigated water characteristics were:  dissolved oxygen, visibility, salinity, total suspended solid (TSS), alkalinity, total phosphorus and Ammonium (NH4).  On the other hand, there was no significant difference between the two studied pond groups concerning each of temperature, pH, electric conductivity (EC), Hardness, nitrate (NO3) ammonium (NH3) and chlorophyll ―a‖.  In general, all investigated values were within the suitable range for tilapia growth.   The abundance of phytoplankton in number was highly significant in the first research pond group concerning each of Cyanophyta, Euglenophyta, and Microcystis aeruginosa in blooming, and was not significant in Baciloarophyta and Chlorophyta.  In addition, Zooplankton was significant in numbers concerning Cladocera, Rotifers and Copepoda and was not significant in total zooplankton number.  Fish and Artemia exposed to pond with Microcystis blooming died within 24 hours.   The research drew the attention towards conducting more future research studies in this concern as a way to control the toxic algae of Microcystis aeruginosa in fish ponds.