| dc.description.abstract | Aquaculture offers the opportunity for safeguarding local and global food security in
the face of declining capture fisheries. However, the form of aquaculture that is
commonly practised in Kenya is characterized by the use of agrochemicals such as
fertilizers that negatively impact biodiversity especially when effluents from fish ponds
drain into water bodies. This study aimed to determine differences in growth rate of
Clarias gariepinus, an important aquaculture fish in Kenya, to assess plankton
diversity, and to identify phytoplankton species associated with pollution under organic
and inorganic fertilization regimens using chicken manure, Diammonium phosphate
and urea, respectively. Average growth rate calculated per day was higher in the
organically-fertilized ponds at 0.06 cm/day, followed by inorganically-fertilized ponds
at 0.05cm/day and then, the control at 0.04 cm/day. Average weight gain was higher in
organically-fertilized ponds at 0.08 g/day followed by ponds fertilized with inorganic
fertilizer at 0.07 g/day and the control, at 0.06g/day. There were significant differences
in growth rate across fertilization regimens (length: F2, 264 = 24.06, p = 0.0399; weight:
F2, 264 = 20.89, p = 0. 0457). Specifically, although differences in growth rate of fish in
organically and inorganically fertilized ponds were not significant, fish in fertilized
ponds were on average, longer and weighed more than those in the control pond.
Jaccard’s similarity index for phytoplankton was highest (0.38) between organicallyfertilized ponds and control but lowest (0.25) between inorganically-fertilized ponds
and control. Use of chicken manure produced the highest diversity of zooplankton
(Shannon-Weiner’s H in organically-fertilized pond = 1.886; inorganic = 1.044, and
control = 0.935). The use of DAP and urea produced the highest proportion of
phytoplankton species associated with pollution. These results do not support the
commonly reported notion that ponds fertilized using inorganic fertilizers are more
productive. Findings suggest that the use of inorganic fertilizers may threaten
biodiversity in aquatic ecosystems through the production of toxic algae. | en_US |
