Fish biology and Ecology in the Uganda Portion of Lake Victoria

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Fish biology and Ecology in the Uganda Portion of
Lake Victoria

• Authors Namulemo G, Wandera S.B, Nkalubo W.
  Aanyu, M., Muhumuza E., Nsega M., Mpaata E.,
  Amiina B.

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Table of Contents

• Introduction
• Objectives
• Sampled areas
• Data collection
• Fish species composition and distribution
• Food and feeding
• Condition factor
• Sex ratios and Maturity
• Conclusions and recommendations

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Introduction

• The number of species in the lake has reduced and
  some are believed to be extinct
• 2/3 of the Nkejje species have been lost
• Decrease in number of species is due to species
  introductions, over-fishing, environmental
  degradation, pollution, etc
• The surviving native species are confined to
  rocky and vegetated habitats
• Size of maturity, sex ratios, and the health of
  Nile perch have changed

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Objectives

• To monitor changes in fish species diversity
• To monitor changes in the biology and ecology of
  Nile perch and Nile tilapia
• Provide information for the sustainable
  management of the fisheries resources

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Sampling area

• Zone 1 Kasensero
• Ddimo, Lambu
• Zone 2 Bunjako, Sanga, Kiyindi
• Zone 3 Buluba, Bugoto, Majanji

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Data collection

• Gill nets were used in the shallow sheltered bays
• A Bottom trawl net was used in the deeper (more
  than 4m) open waters

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Fish species composition and distribution

• Species composition
• 22 species were recorded from the shallow
  sheltered bays and 10 from the open water
• Nile perch was the most dominant.
• 98.2 of Nile perch in the shallow sheltered bays
  were below 50cm Total Length (TL).
• Increase in the proportion of Nkejje in the
  catches was noticed.

• Species distribution
• More species were recorded from Zone 3 (20) than
  in Zone 1 (18) and zone 2 (12).
• More species were recorded from riverine habitats
  (20) than Vegetated (17) and rocky (14) habitats
• Semutundu, Kasulu, Nzeere,Ningu and some Nkejje
  species were confined to rocky and riverine
  habitats

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Food and feeding

• Food of Nile perch
• Fish and Caridina were the main food items in
  open water
• In sheltered bays, Nile perch also fed on insects
  and snails
• Bigger Nile perch (gt50cm TL) fed mainly on fish
• The fish eaten include Nkejje, Mukene and young
  Nile perch

• Food of Nile tilapia
• In zone 1 Nile tilapia fed mostly n insects
• In Zone 2 and 3 algae and fish (Mukene) were the
  dominant foods
• Other food items include water weeds, detritus,
  snails and copepods

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Condition factor (health)

• Nile perch
• It has improved from 1.24 recorded in 1992 to
  1.39 calculated from the recent surveys

• Nile tilapia
• It was calculated at 1.75

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Sex ratios and maturity

• Nile perch
• The proportion of female Nile perch has increased
  from 63 to 72 for 100 males
• Most Nile perch were found to mature at 54cm TL
  but the female mature at 66cm TL
• The smallest mature male was 35cm while the
  smallest mature female was 50cm TL

• Nile tilapia
• The Nile tilapia population is also male
  dominated at a ratio FM of 11.8
• Most Nile tilapia was found to mature at 27cm TL
  for both male and female

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Conclusions and recommendations

• Conclusions
• Shallow sheltered bays are fish diversity
  hotspots and nursery grounds for Nile perch
• The proportion of female Nile perch has increased
  and the fish mature at a smaller size to counter
  over-fishing
• The health of Nile perch has improved due to
  availability of abundant suitable fish food, the
  Nkejje
• Mukene and Caridina are food for many fishes
  especially Nile perch

• Recommendations
• Fishing in shallow sheltered bays should be
  prohibited to protect the young of Nile perch and
  endangered native fish species
• Further stunting of Nile perch should be avoided
  through reduction in fishing effort
• Commercial harvesting of Mukene, Nkejje and
  Caridina should be controlled in order to sustain
  the Nile perch fishery

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Thank you for Listening