Control of bloom in a tropical lake: grazing efficiency of some herbivorous fishes.
Field and laboratory experiments were conducted during 1995 to examine the grazing efficiency of silver carp (Hypophthalmichthys molitrix), bighead (Aristichthys nobilis) and tilapia (Oreochromis niloticus) for controlling Microcystis bloom in a eutrophic shallow lake in West Bengal, India. Results indicated that the introduction of twelve 3-month-old specimens of any of the species into a limnocorral (500 litres) led within 3-7 days to a dramatic reduction (60-93%) of the Microcystis population from an initial density of 18.4-19.3×105/litre2. A 6-180% nutrient enrichment of the system was attributed to defaecation and indicated the potential for ichthyoeutrophication. For clearance of bloom, efficiency was in the order: silver carp > bighead > tilapia, while the ichthyoeutrophic potential was in the reverse order.