On the diet of Nile tilapia in two eutrophic tropical lakes containing toxin producing cyanobacteria
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Date
2011
Journal Title
Journal ISSN
Volume Title
Publisher
Limnologica
Abstract
Due to the production of toxins, cyanobacteria may adversely affect economically important fish such as
Nile tilapia Oreochromis niloticus in tropical lakes. We studied the diet composition and factors affecting
the diet of Nile tilapia in two tropical lakes where cyanotoxins were present. Particle-bound microcystins
were present in all analysed water samples, ranging in concentration from 0.00012 to 1.11 and from
0.006 to 0.254 mg L1 in Murchison Bay in Lake Victoria and Lake Mburo, respectively. Detritus and
phytoplankton were the main dietary components of the Nile tilapia, with phytoplankton contributing to
over 30% by volume of stomach contents. The cyanobacteria Microcystis spp., which are also the most
likely source of microcystins in the lakes, accounted for more than 80% of ingested phytoplankton.
Microcystis spp. were also the most abundant cyanobacteria in both lakes (460%). We found no
significant relationship between the contribution of phytoplankton in Nile tilapia diet and the
concentration of microcystins in the water but we found a close association between water transparency
and the contribution of insects to Nile tilapia diets in Murchison Bay. Our results further show that none
of the other measured environmental variables was a good predictor of diet items in Nile tilapia. Adult
Nile tilapia in our study lakes, rely heavily on filter feeding, particularly under conditions of low water
transparency, trapping detritus and phytoplankton cells especially colonies. They can ingest more
mobile prey like insects and insect larvae when the water transparency and visibility increases.
Description
Keywords
Nile tilapia, Diet, Microcystins, Cyanobacteria, Tropics
Citation
Semyalo, R., Rohrlack, T., Kayiira, D., Kizito, Y. S., Byarujali, S., Nyakairu, G., & Larsson, P. (2011). On the diet of Nile tilapia in two eutrophic tropical lakes containing toxin producing cyanobacteria. Limnologica, 41(1), 30-36. doi:10.1016/j.limno.2010.04.002