Browsing by Author "Outa, Nicholas"

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  • Publication
    Publication
    Some aspects of the biology of Nile perch, Lates niloticus, in the open waters of Lake Victoria, Kenya
    (Wiley, 2017-09-14) Yongo, Edwine; Outa, Nicholas; Kito, Keiko; Matsushita, Yoshiki
    Samples (6404) of Nile perch were collected monthly from commercial catches between June 2014 and June 2015. The total length (cm), weight (g) and sex of fish were all determined in the field, with 3771 (59%) being male and 2059 (32%) being female fish, for an overall sex ratio of 1.83:1.00 (male: female). The average length and weight for all fish were 55.38 ± 0.14 cm TL and 2355.10 ± 22.30 g, respectively. The size of male fish ranged from 15.5 to 128.5 cm TL and weighed between 190 and 25 000 g, whereas that of female ranged from 21.0 to 130.0 cm TL and weighed between 124 and 25 800 g. The value of the regression slope b of the length–weight relationship was equal to 3.04. The mean (±SD) condition factor for all fish was 1.23 ± 0.13. The condition factor was different in the length groups, with the highest (1.32 ± 0.13) and lowest (1.12 ± 0.20) values recorded in length groups 100–110 and <30 cm TL, respectively. The highest and lowest condition factors were recorded between January and March, respectively. The length–weight relationship and condition of Nile perch in Lake Victoria have deteriorated greatly, this finding being linked to the reduction of its prey species in the lake.
  • Publication
    Publication
    Spatial distribution and abundance of zooplankton communities in Lake Victoria, Kenya
    (International journal of fisheries and aquatic research, 2017-04-22) Yongo, Edwine; Outa, Nicholas
    The study was conducted between January and March 2015 in the Kenyan waters of Lake Victoria. Duplicate composite vertical samples of zooplankton were collected from the water column using 50μm plankton net of 30 cm diameter and preserved with 5% formalin prior to identification in the laboratory. Water quality parameters were also measured in-situ. Cyclopoid copepods (64.7%) dominated the zooplankton community while Rotifers (1.7%) were the least abundant in the lake. A total of 20 zooplankton species were identified under the taxa 9 Rotifer, 6 Cladoceran, 4 Cyclopoid and 1 Calanoid. Multiple comparisons by Tukey test showed no significant difference in zooplankton density among the stations (p>0.05). The highest values of water quality parameters recorded were turbidity 70.52 mgL-1 , conductivity 158.72 μS/cm, temperature 27.38 o C, Dissolved Oxygen 5.25 mgL-1 and pH 8.06, with corresponding lowest values of 11.09 mgL-1 , 93.26 μS/cm, 25.74 o C, 4.35 mgL-1 and 7.41. The observations from the study could be linked to the habitat degradation and pollution causing changes in the zooplankton community in Lake Victoria.