Kabaka's Lake as the name implies, is a lake that belongs to the Buganda Kingdom which is under the Kabaka of Buganda (King of Buganda) and is located in the central portion of Kampala city. At the launching of "Food for all in Buganda" campaign during November 1999 at Nfuufu in Mukono District -Uganda, National Agricultural Research Organisation (NARO) was requested to find means of reactivating the fishery potential of the lake. The lake had been stocked with the Nile perch (Lates niloticus & T. zilli) during 1950s and the fishery was not being efficiently exploited. After restocking, no monitoring was done and therefore it was not known whether the introduced species established themselves. Restocking was mainly aimed at enabling this lake provide a source of food and recreation. The major objective of the study therefore was to establish the present status of the fishery by determining the fish species composition, distribution, relative abundance, population structure of the major fish species, catch rates in the gill net fishery and the biology and ecology of the dominant fish species. The study was conducted during 200

Kamanyi, J.R.

Mbabazi, D.

English

Aquatic Commons

The Status of the Fish
 
Stocks, the Environment
 
and socio-economics of
 
Kabaka's Lake 
The Fisheries Research Component
 
Lake Victoria Environmental Management Project
 
P.O. Box 343, Jinja 
March 2001 
~ - ----~ ------- --~----~- ---~ -- -­
The fish Stocks of Kabaka's Lake 
By J. R. Kamanyi & D. Mbabazi 
Introduction 
Kabaka's Lake as the name implies, is a lake that belongs to the Buganda Kingdom 
which is under the Kabaka of Buganda (King of Buganda) and is located in the central 
portion of Kampala city. At the launching of "Food for all in Buganda" campaign during 
November 1999 at Nfuufu in Mukono District - Uganda, National Agricultural Research 
Organisation (NARO) was requested to find means of reactivating the fishery potential 
of the lake. The lake had been stocked with the Nile perch (Lates niloticus & T. zillil) 
during 1950s and the fishery was not being efficiently exploited. After restocking, no 
monitoring was done and therefore it was not known whether the introduced species 
established themselves. Restocking was mainly aimed at enabling this lake provide a 
source of food and recreation. The major objective of the study therefore was to 
establish the present status of the fishery by determining the fish species composition, 
distribution, relative abundance, population structure of the major fish species, catch 
rates in the gill net fishery and the biology and ecology of the dominant fish species. 
The study was conducted during 2000. 
Materials and methods 
Experimental fish sampling was carried out using graded gill net mesh size nets ranging 
from 25.4mm (1 ") to 203.2mm (8"). The 25.4mm to 152.4mm (6") nets increased by 
12.7mm (0.5") intervals while the rest increased by 25.4mm (1 "). The three gill net 
fleets used were set in various locations so as to cover the different lake habitats 
including bareshoreline, vegetated shoreline, and open waters. The nets were set 
overnight and retrieved the following morning. The fish from different mesh sizes of 
nets and locations were sorted into their taxonomic groups (species) the number and 
weight of species were recorded. For each of the species, biometric data that included 
total length, standard length, weight of individual fish (g), sex, maturity state, stomach 
fullness based on scale when 1=full stomach through %, Y. Y:. to O=empty. Where 
possible the food contents were identified in the field while others especially the 
tilapiines (Ngege) stomachs were preserved in 10% formalin for subsequent laboratory 
analysis under the microscopes. The relative importance of different food items were 
located points according to Hynes, 1950. Where eggs were mature as in C/arias 
gariepinus these were preserved in 50% alcohol and egg count carried out in the 
laboratory using an egg counter. 
Results 
Fish species composition 
Four fish species namely L. niloticus (Mputa) - Nile perch, Tilapia zillii (Kajjansi) ­
Tilapia, Oreochromis leucostictus (Ngege) - Tilapia, Clarias gariepinnus (Male) ­
2 
Catfish were recorded in Kabaka's lake during 2000 experimental gill net fishing. T. zillii 
was the dominant species by number contributing 61.1 % followed by L. niloticus 
(19.8%), O. leucostictus (17.6%) and C. gariepinus (1.5%) - (Fig. 1a). Based on 
species composition by weight, the dominant species in order of importance were L. 
niloticus (65.2%), C. gariepinus (20.4%), T. zillii (11.3%) and O. leucostictus (3.1 %) ­
Fig.1b. 
Fish species distribution and relative abundance 
Of the four major fish species on Kabaka's lake 57% by weight of the overall fish 
species caught were in the open waters followed by 22.8% in the bare shoreline and 
19.6% in the vegetated shoreline Table 1. C. gariepinus and L. niloticus were mainly 
dominant in the open waters, while O. leucostictus and T. zillii were concentrated in the 
vegetated shoreline (Table 1 & 2). 
Based on percentage by number, 45.3% of the overall number of fish was located in the 
vegetation habitats (Table 2) contributed by mainly the tilapiines especially T. zillii 
followed by open waters (32.7%) and bare vegetation (22.1%). 
Size at first maturity 
The size at first maturity i.e the size at which 50% of the fish in a population are mature 
was 17cm for T. zillii and 18cm for O. leucostictus. All the L. niloticus and C. gariepinus 
caught in experimental gill net catches were mature. 
Sex ratio (Males: Females) 
The sex ratios were 1.4:1, 4.6:1, 1.2:1 and 1:1 for L. niloticus, O. leucostictus, T. zillii 
and C. gariepinus respectively. 
Mean catch rates 
The highest mean catch rates (g/netlnight) were recorded in the 127.0 mm, 177.8mm, 
152.4mm mesh size nets as 4160g, 3931g, 3215g respectively (Table 3) and the 
catches were of L. niloticus and a few but large C. gariepinus. In the smaller mesh size 
nets below (88.9mm) the highest mean catch rates 704g recorded in the 76.2mm mesh 
size nets were contributed by T. zillii and a few O. leucostictus. The overall mean catch 
rate (g/netlnight) was 1408g. 
Size structure of the major fish species 
The length frequency distribution of three major fish species on Kabaka's lake is shown 
in Figures 2 and 3. The size ranges of O. leucostictus and T. zillii were 8-28cm TL and 
7-30 cm TL with model classes at 15cm TL and 11 cm TL for O. leucostictus and T. zillii 
respectively (Fig. 2). The length frequency distribution of L. niloticus had a range of 38­
78cm TL with a mode of 52cm TL (Fig. 3). There were no juvenile L. niloticus. All the 
3 
fish both males and females of (38-78cm TL) were mature. As with L. niloticus, there 
were no juveniles of C. gariepinus encounted during the experimental fishing. The 5 
fish caught had a size range of 81-104cm TL and all the fish were mature. The absence 
of juveniles L. niloticus and C. gariepinus indicates that there is no reproduction. 
Fecundity: 47,068 eggs were counted in C. gariepinus of 94.0 TL. 
Food and feeding 
The percentage contribution of different foods based on point method (Hynes, 1950) for 
the different food items encountered as shown in Fig 4. 55 specimens of T. zillii 
stomachs (size range 9.5 - 26.5cm TL) were examined for food. 70.9% of the 
stomachs had food. 21 specimens of O. leucostictus (size range 13.8 - 24.9cm TL) 
were examined and 33.3% of the stomachs had food. 
The two tilapiines (T. zillii and O. leucostictus) in order of importance fed mainly on blue 
green algae, green algae and higher plants. Higher plant material dominated followed 
by detritus material, blue green algae in T. zillii while the dominant food items in O. 
leucostictus were blue green algae followed by detritus material, green algae and higher 
plant material. In addition, sand grains, chironomid larvae and pupae, chaoborus pupae 
and insect remains were found in the stomach contents of T. zillii. 50 stomach 
specimen of L. niloticus (size range 37.0 - 76.2cm TL) were examined. 36% of the 
stomachs had fish food mainly fish remains. The fish that could be identified included T. 
zillii, Clarias spp and Aplochyleicthys. The 4 specimens of C. gariepinus examined 
(size range 81-98cm TL) had empty stomachs. 
Fecundity: the egg count of the only one female C. gariepinus of 94cm TL was 
47,060eggs 
Discussion 
In terms of weight, Kabaka's lake was dominated by the introduced L. niloticus. L. 
niloticus in this lake lacked juveniles, which implies that there is no recruitment. This 
observation may not enable sustainability of the fishery if exploitation started on the 
lake. The excessive environmental degradation and pollution through several human 
activities like the lake being used as a dumping ground, washing bay for cars and 
clothes has led to low invertebrate diversity (Ndawula, 2000 unpublished report) thus 
reducing food availability to fish. Water quality management is known to be one of the 
most factors in ensuring a healthy fish population and affects the health and 
reproduction of fishes while heavy particulate matter bury the eggs and larvae of benthic 
organisms upon settling at the bottom of the lake thus affecting the aquatic life 
(Natividad, 1984). Excessive pollution can also lead to low dissolved oxygen. Nile 
perch requires above 5mg/L of dissolved oxygen for proper growth and reproduction. 
Pollution could be the major cause of restricted recruitment of the major fish species. 
Most fish require a minimum ideal oxygen concentration of 5mg/L (Natividad, 1984). 
4 
Conclusion 
Kabaka's lake though with some fish cannot support a viable fishery at the moment due 
to excessive pollution and eutrophication and absence of recruitment especially in the 
major fishery - the Nile perch. 
Recommendations 
•	 The lake should be drained and the bottom cleared in preparation for fresh clean 
water after which the lake can be restocked with appropriate fry. 
•	 The lake should be fenced off to avoid further contamination 
•	 There is need to investigate whether the present fish in this lake is fit for human 
consumption 
References 
Hynes, H.B.N, 1950. The food of freshwater sticklebacks (Gastostens aculeatus and 
Pygostens pungitins) with a review of methods used in studies of the food of fishes. J. 
Anim. Ecol. 19:36-58. 
Cher vinski, 1984. On water temperature (In Phillipina (BFAR) Freshwater aquaulture 
extension training mannual Vol. III. 
Natividad J.M. 1984. Water quality management. In Philippine (BFAR) Freshwater 
Aquaculture Extension Training Manual volume III Pg. 53-60. Technology Bureau of 
Fisheries and Aquatic Resources United States Agency for International Development. 
Table 1. Fish species distribution and relative abundance by weight in different habitats on 
Kabaka's lake (2000) 
Habitat % Clarias % Lales % Oreochromis % Ti/apia zi/Iii % Overall 
gariepinus ni/oticus leucostictus 
Bare shoreline 17.4 24.2 27.3 23.1 22.8 
open water 82.6 56.9 32.8 23.6 57.6 
Vegetated shoreline 0.0 18.9 39.8 53.3 19.6 
Table 2. Fish species distribution and relative abundance by numbers in different habitats on 
Kabaka's lake (2000) 
Habitat % Clarias % Lates % Oreochromis % Tilapia zi/lii % Overall 
gariepinus niloticus Jeucostictus 
Bare shoreline 20.0 23.9 25.4 20.5 22.1 
open water 80.0 56.7 37.3 228 32.7 
Vegetated shoreline 0.0 19.4 37.3 56.6 45.3 
5 
(a) 
17.6% -1~~~~19.8% 
61.1% 
~ Lares niloricus 
(b) ~ Tilapia zillii 
3.1 % 
• Clarias gariepinus 
o Oreochromis leucosricrus 
Fig. 1 Percentage composition by number (a) and by weight g (b) of the different fish 
species caught by gill net mesh sizes of25.4-203 mm in Kabaka' slake (2000). 
16 Oreochromis leucostictus 
N=49 
14 
Size at 50 % maturity 
12 
10 
~ 
1 
= 8 
6 
4 
2 
O+-~-
16 
Tilapia zitlii 
14 N=98 
_ Size at 50 % maturity 
12 
10 
....
... 
1:1 
'" = 8 
'" '" ~ 
6 
4 
2 
o 
6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 
Total length (em) 
Fig.2 Length frequency distribution of Oreochromis leucostictus and Tilapia zillii
 
caught by gill nets of 25.4-203.2 rnm mesh size in Kabaka's lake.
 
16 (N=67) 
24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78
 
Total length (em)
 
Fig.3 Length frequency distribution of Lares niloricus caught by gill nets of 25.4-203.2
 
mrn mesh size in Kabaka's lake.
 
---
40 Tilapia zillii 
35 N=33 
30 
25 
20 
15 
10 
5 
0 
45, Oreochromis leucostictus 
0 40..
..." N=17 
..
..c= 35 
..
... 30 
0 "
'" 
25 
OJ) 
S '" 20 
5 15 
~ 10 ~ 
5
 
0
 
Lates niloticus 
80 ~ 70 N=28
 
60
 
50
 
40
 
30
 
20
 
10
 
0 
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.E '"bll " .S ~ '"1:; 0. " 0. ::::: '">. .S 
0. 
t:: <;j ~ '" ~ B '" '<a" '-'- -5 ..,'" 
'" bll'" 
..!S " 0. 5- S '-N .>l s'" Cl"
"0 S'" "0 "0 ~ .S .Sl " ~ .~" 
~ 
" 
·s '" 2 >. " §- ..c::
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"
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's
0 
.0 
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.s" 2 "~ '" 0.~ 
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Food items 
Fig 4 Percentage contribution of the different food items found in the stomachs of Tilapia 
zillii, Oreochromis leucostietus and Lates niloticus caught using gillnets in Kabaka's lake. 
Table 3. Mean catch rates (grams per net per night) on Kabaka's lake (2000) 
Gear size (mm) g/netlnight 
25.4 75.9 
38.1 243.5 
50.8 619.7 
63.5 251.7 
76.2 703.5 
88.9 513.0 
101.6 841.5 
114.3 1383.5 
127.0 4160.0 
139.7 1690.0 
152.4 3215.0 
177.8 3931.0 
203.2 675.0 
Major physio-chemical and biological properties of Kabaka's Lake 
Naluwayiro J. & Magezi G. 
Introduction 
Kabaka's lake lies within the densely populated Kampala City. The lake is important as 
a reservoir of clean water for recreational and other use is being threatened by water 
degradation due to intense anthropogenic activities, including car-washing, around the 
lake. Devegatation of the shorelines and damping garbage into the lake are already 
contributing to undesirable water quality effects such as objectionable colour and high 
oxygen demand in bottom waters. 
Materials and Method 
Sampling for major physico-chemical parameters and phytoplankton was conducted in 
year 2000 and in conjunction with invertebrate and fish survey undertaken by 
researcher at FIRRI. Methods of analysis for nutrients followed standard procedures as 
described in Stainton et al. 1977 and Lab manual, FIRRI, 1996. 
Results 
High dissolved oxygen concentrations (> 8 mg/L) were often measured in surface 
waters « 1 m), while corresponding bottom waters (> 1 m) remained hypoxic to anoxic 
throughout the day (Figure 1). The high dissolved oxygen concentrations in surface 
waters were a result of high photosynthetic activity as indicated by elevated rates of 
areal algal productivity, in the range 4470-6910 mg.m-2.h-1 (mean 5690 mg.m-2 .h-1). 
6 
Daily phytoplankton primary productivity was in the range of 42 to 66 g 02.m-2.d-1 and 
indicative that Kabaka's lake was one of the most productive water bodies in the world 
and has the potential to support a highly productive pelagic fishery. However, 
photosynthesis occurs within a shallow euphotic zone of < 1.0 m due to rapid light 
attenuation indicated by the high light extinction coefficients (4.3 -6.7 m-1)(Table 1). 
There is no doubt that the high algal biomass (41.7-240.8 mg.m-3) contributes to the 
rapid light absorption in the surfaces of the lake. Besides, light absorption by a huge 
chloropyll-a biomass and other particulate matter can result in diurnal heating and 
elevated surface temperatures as observed in Kabaka's lake. 
The high algal biomass and productivity in Kabaka's lake are a result of high nutrient 
concentrations recorded in the water column (Table 2.). There are low algal species 
diversity of algae in this lake and blue green algae were the most dominate group. Total 
phosphorus and dissolved inorganic P concentrations of Kabaka' lake were among the 
highest in the world. Total P varied 12-fold within the lake (Table 2) and its average 
value was 12 times higher compared to the average total P value of Lake Victoria. 
The high total P concentrations in the lake allows proportionate use of nitrogen by the 
algae resulting in high total N concentrations in the lake. However, the hardly 
measurable dissolved oxygen concentrations in mid to bottom waters threats nitrogen 
return to the productive euphotic zone and may have consequences for algal species 
composition, which in turn will affect the structure and composition of higher trophic 
levels. Preliminary data of sestonic ratios indicate that Kabaka's lake has one of the 
lowest recorded TN: TP ratios « 2.0) for a shallow water body. Persistence of low TN: 
TP ratios will likely result in dominance of blue-green algae that are poor quality food for 
fish. (Tailing et.a/1996) 
Conclusion 
High nutrient concentrations are the initial force driving high algal biomass and 
productivity in Kabaka's lake. Increased nutrient input to the lake will enhance 
proliferation of the blue green algae, which in turn undermine the water quality of the 
lake. However, low TN: TP indicate excess P that creates N -demand, which in turn will 
force the lake to get the required N loading from the atmospheric N source. 
Consequently blue-green algae will dominate the lake and will further undermine the 
use of Kabaka's lake as source of safe water. 
Recomendation 
Malpractice that lead to increased nutrient inputs into the lake should be minimized so 
as to improve and maintain an acceptable water quality for human and animal use. 
7 
Table. 1.Physical parameter of Kabaka's lake 2000. N= number of samples 
Cond(us/cm) Do (mg/l) Temp eC) PH Secchi(m) 
Min 138 0.0 23.0 6.4 0.4 
Max 219 14.4 29.6 9.3 0.8 
Mean 192.0 5.5 25.5 7.9 0.5 
Std 13.6 3.4 1.3 0.6 0.2 
N 184 189 106 105 12 
Ext. coef. 4.3-6.7m 
Table. 2. Average nutrient and chlorohyll-a concentrations of Kabakas during 2000. 
N = number of samples 
TN (uM) TP (uM) SRP(uM) SRSI(uM) Chir-a(ug/l) 
Min 9.0 8.9 1.6 19.2 41.7 
Max 242.9 109.7 35.0 27.4 240.8 
Mean 36.6 24.1 7.8 22.2 132.5 
Std 58.6 25.4 10.5 26 52.0 
N 16 16 16 16 16 I 
8 
Table 3. Algal speceis diversity in Kabaka's lake 
cynobacteria 
Merimopedia elagans p 
Merismopedia tenussima p 
Merimopedia spp p 
Microsystis aeruginosa p 
M.incerta p 
M.ftosaque p 
M. wasarbagi p 
Coelespherum p 
p.circumerenta p 
Oscillatoria limnetica p 
Anabeanopsis p 
Anabeana circinalis p 
planktoiyngbya p 
Chrococcus p 
Chlorophyta 
Oosytis p 
Anks.falactus p 
Scenedesmas p 
Stuarastrum p 
Tetreadron trigonum p 
pediastrum simplex p 
Cosmarium p 
Scenedesmas quadricauda p 
Scenedesmas Arcuatus p 
Scenedesmas Castato p 
Monorophidium p 
Bacillariophyceae 
Cyclotella p 
Nitzchia p 
Euglenophyta 
Trachelomonas armatus p 
phacus p 
Eugiena Acus p 
pyrrophyta 
Glenodinum p 
Ceratium hirudinella p 
protozoa 
Ciliate p 
Vorticeila p 
Total 34.00 
Reference: 
Stanton,M.P,M.J Capel and F.A JAmstrong,1997. The chemical analysis of fresh water.Fish.Mar.Serv.
 
Msc Spec. Pub!. 25:16p.
 
FIRR,1996 .Laboratory manual. 
9 
- - -- --------------v 
E E ::; E E ::; E E E ::; ::; 
0. 0. 0. 0. 0.<: 0- <: <: ?ia a aa a a '" a '" a aa a a a a a a a a a a 0 0 8<ci ai <ci ai M <ci ai M <ci
" " " 
~~ 
Time (Hrs) 
--+- Edge1 -----.- Mid Edge 2 
Fig.1 Disslved oxygen at 1m depth at various times in Kabaka's lake. 
10 


The fish stocks of Kabaka's Lake

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The fish stocks of Kabaka's Lake

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