ASSESSMENT OF THE DISTRIBUTION, ABUNDANCE AND DIVERSITY OF PLANKTON AND FISHES ALONG A SALINITY GRADIENT IN THE LAKES NAIVASHA AND OLOIDEN, KENYA

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.