Abstract:
A study was conducted monthly, for a year along a transect in seven sampling sites. The objective
of the study was to assess the distribution, abundance and diversity of plankton and fish along a
salinity gradient in the Lakes Naivasha and Oloiden. Physical-chemical parameters such as lake
depth were measured in situ and Water samples for nutrients and others were collected for
laboratory analysis. Fish were caught using gill nets and Oreochromis niloticus gut sample was
taken immediately for later laboratory analysis. The Lake Oloiden had a depth and secchi depth of
6.5 ± 0.2 m and 49.3 ± 1.53 cm while the Lake Naivasha’s were 7.73 ± 0.35 m and 61.2 ± 1.3 cm
respectively. Temperature, dissolved oxygen, conductivity, salinity and pH for the Lake Oloiden
were as follows: 21.54 ± 2.19 oC, 9.58 ± 1.75 mg/L , 0.58 ± 0.1 µS/m, 310 ± 65 ppm and 8.51 ±
0.3, while Lake Naivasha’s were; 21.12 ± 1.91 oC, 6.19 ± 0.94 mg/L, 0.18 ± 0.14 µS/m, 96 ± 20
ppm and 7.58 ± 0.26 respectively. Thirty-two phytoplankton, seventeen zooplankton and 9 fish
species were identified. The Shannon-Wiener index, evenness and Margalef’s index were: 0.72 ±
0.1, 0.73 ± 0.06, 3.72 ± 0.77 for the phytoplankton while zooplankton's were; 0.47 ± 0.09, 0.81 ±
0.13, 4.41 ± 0.8 while fishes' were; 0.33 ± 0.3, 0.52 ± 0.44 and 1.52 ± 0.71 respectively.
Oreochromis niloticus fed on algae (61.63 ± 17.35 %), detritus (23.11 ± 14.4 %), other plant
material (16.64 ± 12.35 %), fish parts (14 ± 5.16 %) and zooplankton (12.92 ± 5.8 %). The
diversity index and evenness index were low while richness index was high for the
phytoplankton, zooplankton and fish respectively. Salinity and conductivity were lower compared
to previous finding. Research should be done on the chlorophyll-a, nutrients and plankton at
various depth.
