Feminist Trends in Achebe's Postcolonial Novels

82 Pages·2014·0.28 MB·English

ADDIS ABABA UNIVERSTY
SCHOOL OF GRADUATE STUDIES
FACULTY OF SCIENCE
DEPARTMENT OF BIOLOGY
THE EFFECTS OF STOCKING DENSITY AND FEED ON THE GROWTH
PERFORMANCE OF Oreochromis niloticus IN SUSPENDED CAGE IN
LAKE BABOGAYA, ETHIOPIA
BY
KEMAL MOHAMMED
June, 2008
THE EFFECTS OF STOCKING DENSITY AND FEED ON THE GROWTH
PERFORMANCE OF Oreochromis niloticus IN SUSPENDED CAGE IN
LAKE BABOGAYA, ETHIOPIA
A THESIS PRESENTED TO THE SCHOOL OF GRADUATE STUDIES
ADDIS ABABA UNIVERSITY
IN PARTIAL FULFILLMENT OF THE REQUIREMENT FOR THE
DEGREE OF
MASTER OF SCIENCE IN BIOLOGY
By
Kemal Mohammed
June, 2008
Acknowledgement
I am very grateful to Dr. Abebe Getahun, my advisor, for his keen interest in my work and
for the financial and technical support that enabled me start the research in time. I appreciate
and thank him for the prominent suggestion and critical reading of the manuscript and
consistent support while writing the paper. I gratefully thank Dr. Seyoum Mengistu for his
support inthe selectionofthe culturesiteand providingboat.
I am grateful to Dr. Zenebe Tadesse in his consultancy starting from project design to the end
of the project. I also thank Redeat H/Selassie for his technical support, and as a whole,
Sebeta Fish and Other Aquatic Life Research Center in providing cage construction materials
and enthusiastic technical support in the construction of cages, and IRLI (Debre-Zeyit) in
providing access to the culture site, guarding service and other cooperation in the whole
experimental period.
I wish to thank my colleagues, Getachew Tadesse, Afework Kara, Denbere Belay and Moges
Beletew for their cooperation and moral support. Moreover, my great thanks should go to my
beloved friends Ato Solomon G/Tsadik and Ato Fasil Dawit for their unreserved help and
support. Especially, my family Munir Nesredin and Haji Nesredin Yesuf and my beloved
wifeRadya Workuarethanked for theassistance inallnecessities.
Finally, my thank go to Addis Ababa University, Department of Biology and the
Development Innovative Fund (DIF) through the Zoological Natural History Museum, for
thefinancial assistance and forbothfield andlaboratory facilities.
Praise be to Allah, Most Gracious, Most Merciful
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Table of Contents
Acknowledgement................................................................................................................i
List of Tables......................................................................................................................iv
List of Figures......................................................................................................................v
ABSTRACT......................................................................................................................vii
1.INTRODUCTION...........................................................................................................1
2.LITRATURE REVIEW...................................................................................................9
3.OBJECTIVE..................................................................................................................14
3.1. General objective.................................................................................................14
3.2. Specificobjectives...............................................................................................14
4.DESCRIPTION OFTHE STUDYLAKE....................................................................15
4.1. Lake Babogaya (Bishoftu-Guda).........................................................................15
4.2. Meteorological data.............................................................................................17
5.MATERIALS AND METHODS..................................................................................19
5.1. Jettyconstructionandplacement.........................................................................19
5.2. Structural designand constructionofcages........................................................19
5.3. Sourceof Juveniles..............................................................................................20
5.4. Stocking...............................................................................................................20
5.5. Feedand feedingrate...........................................................................................20
5.6. Physicochemical parameters................................................................................22
5.7. Identificationand estimationofphytoplanktonand zooplanktonspecies...........22
5.7.1.Estimatingthebiomass ofphytoplankton....................................................22
5.7.2.Estimatingthebiomass ofzooplankton.......................................................23
5.8. Gut analysis.........................................................................................................23
5.9. Durationof theexperiment..................................................................................24
5.10. Data collectionandanalysis................................................................................25
6.RESULT........................................................................................................................27
6.1. Physico- chemical parameters.............................................................................27
6.2. Majornatural feed at theculture site...................................................................28
6.3. Gut contents.........................................................................................................29
6.4. Growth performance............................................................................................30
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6.5. Meanweight........................................................................................................30
6.6. Dailygrowthrate.................................................................................................32
6.7. Specificgrowth rate.............................................................................................33
6.8. Feedconversionratio...........................................................................................35
6.9. Production............................................................................................................36
6.10. Lengthofdifferent stocking densities duringthesamplingtime........................36
6.11. Fultonconditionfactor........................................................................................37
6.12. Length-weigh relationship.................................................................................38
7.Discussion......................................................................................................................39
8.CONCLUSIONAND RECOMMENDATION............................................................49
REFERENCES:.................................................................................................................51
APPENDICES...................................................................................................................67
iii
List of Tables
Table1: Somemorphological,physical andchemical characteristics ofLake Bishoftu-Guda
(Babogaya).....................................................................................................................................17
Table2: Stockingdensity, initial mean weight andlengthofthe stock........................................20
Table3: Percentage ofcarbohydrate, fat andproteinfoundineachfeeditem............................21
Table4: Compositionoffeed(%).................................................................................................21
Table5: Physical parameters result at theculture siteofLake Bishoftu-Guda.............................27
Table6: Identified zooplanktons oftheculture siteofLake Bishoftu-Guda................................29
Table7: The T–test values andstatistical relations of Feedand ControlStocks........................31
Table8: Five-monthsummarydataof different stockingdensities..............................................34
Table9: Summarydata ofthestocks after five months................................................................35
Table10: Average length values ofdifferent stockingdensities ofsamplingperiod..................37
Table11: Lengthweight relationshipofthestocked fishes after fivemonths..............................38
Table12: Percentage ofstockedand wildfishes (obtained from eachstockat harvestingtime).38
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List of Figures
Figure 1: LocationofBishoftu-Guda (Babogaya),inrelationtoother Bishoftucrater lakes after
Lamb(2001) 16
Figure 2: Annual monthlyair temperature in°C,oftheculture site(Source: EIAR,2007). 18
Figure 3: Annual monthlyaverage rainfall inmmofthe culturesite(Source: EAIR,2007). 18
Figure 4: Annual monthlyaverage windspeed m/s ofthe culturesite(Source: EIAR,2007). 18
Figure 5: Pictureshowingthejettyconstructionand cageanchoringsite 19
Figure 6: Surface water temperature result ofculture site 27
Figure 7: Proportionof majornatural feed(from water analysis oftheculture site). 28
Figure 8: Volumetricproportionof majornatural feed(in thegut part). 29
Figure 9: Growthpattern ofdifferent stockingdensities andcontrol stock 31
Figure 10: DGR change pattern of different monthsof stocks inrelationtocontrol 32
Figure 11: Themonthlypercentage DGR ofdifferent stocks 33
Figure 12: MonthlySGRof different stocks inrelationtocontrol 33
Figure 13: Fultonconditionfactor ofthefour feed treatments 37
Figure 14: Fultonconditionfactors oftheST/50feed andST/50non-feed treatments 38
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List of Appendices
Appendix 1:Correlations: ComparisonofDGR,MWT,FCR, SGR,TIMEand G
Appendix2: Volumetricandrelative number proportionsof majornatural feed of
gut analysis.
Appendix3: Percentage proportionofnumber ofmajornatural feed
(wateranalysis of culturesite)
Appendix4: T-Test comparisonrelationship ofFCR tostockingdensity
Appendix 5:T-Test comparisonoflengthrelationshipof thestocks
Appendix 6: Productionof O.niloticus incages andpens, withoutsupplementary feeding*,
inCardona, Laguna deBay, Philippines,1982–83.Cages are 3–5m deep.
Appendix7: Meanweight ofthestocks indifferent samplingmonths
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ABSTRACT
The effects of stocking density and supplementary feeding on growth performance of Nile tilapia, O.
niloticus in cage culture in Lake Babogaya were investigated for five months from February 2007 to
July 2007.Juvenile of O. niloticus havinga mean bodyweight of 30 gm andmean length of 12.5 cm
were stocked in duplicates of five cages, with stocking densities of 50 (with and with out feed), 75,
100 and 125 per meter cube. The feed treatments were providing supplementary feeds with a
composition of 60% sweeping meal, 20% crushed seedcotton and 20% pea flour, witha feeding rate
of 2% of the body weight. The feed was divided equally into two and was fed twice a day. Growth
changeandfeedconversionratioofthestockedfishwerestudiedforthesamplingperiods.
The survival rates of the stocks were high in all treatments and were not affected by difference in
stocking density. The results of this experiment indicated that significantly higher mean weight
(MWT) and daily growth rate (DGR) were obtained from the lower stocking densities with feed (50
fish/m³),thanthosefromthehigherstockingdensities(125fish/m³)andthecontrolstock(50fish/m³)
(P < 0.05).This resultrevealedthat growthperformance was negativelyaffectedbystocking density.
Moreover; feed had a strong positive effect on growth performance. The gut analysis result indicates
the importance rank of natural feed (phytoplankton: Microcystis aeruginosa, Bacileariacaea and
dinoflagellates)were1st,2ndandthe3rdrespectively.ThebiodynamicoftheLakechangedafterApril;
dinoflagellates became more dominant and Microcystis aeruginosa became more decreased, but the
importance rank remain the same throughout the sampling periods, which indicated O. niloticus is
selectivefeeder andMicrocystis aeruginosa,andBacileariacaeaarethepreferrednaturalfeedinLake
Babogaya.
The least growth performance coincided with the decline of primary production, the change in
biodynamic of the Lake and the vertical shifting of the natural feed to metalimnetic region. The
negative growth of the control stock in May andJune indicates that extensive cage culture practice is
impossible while the primary production is decreasing and the natural feeds (phytoplankton and
zooplankton) are shifted tothe lower depth (metalimnetic region) from April to September unless the
size of the cage is big enough to reach to the feed richer site of lower depth, but this has to take the
DOconcentrationintoconsideration.
A nematode parasite worm Contracaecum sp. with length of 2.6 to 4.5 cm and 5 to 7 in number per
fish were identified in the gill cavity of the stocked fishes with size of 60 –100 g; however, frequent
longer sized worms were not common in natural wild fishes of comparable size. But these parasites
rarely occurred in bigger sized wild fish. The competition for feed of the wild fishes was very high
which bring stress and competes for feed and space; during sampling and harvesting times between
17– 89% extra wildfishes were identified. Relativelyimproved growth was observed inthose cages
that were fixed toward shore side and in shallow water than the front linedcages that were hanged in
deeperpositionwhichindicatesthepositionofthecageshaseffectongrowthperformance.
Keywords/phrases:Cageculture,LakeBabogaya,stockingdensity
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1.INTRODUCTION
The world population is on the rise, as is the demand for aquatic feed products, but
production from capture fisheries at the global level is leveling off and most of the main
fishing areas have reached their maximum potential. Meeting basic human needs for protein
feeds in the future will be a difficult challenge. Approximately 1.3 billion people live on less
than a dollar a day and half of the world's population lives on less than 2 dollars a day
(Watson, 1999). For this, aquaculture not only addresses the challenge efficiently but also
gives analternativemeans ingiving jobopportunityand reducingpoverty.
Aquaculture production is highly dominated by Asian countries, China accounted over 90%
of world production, but aquaculture activities are not well developed in Africa. According to
Aguilar-Manjarrez and Nath (1998) Africa has big potential for fish farming with 37 percent
of its surface area suitable for artisanal fisheries and 43 percent suitable for commercial fish
production. Africa has suitable bio-physical resources for aquaculture activities, i.e. the warm
tropics with elevated temperatures and abundant rainfall, unutilized or under utilized land
and low-cost labor as well as high demand for fishery products (Aguilar-Manjarrez and Nath,
1998). Between temperate (23°–67°) and tropical (23°N–23°S) zones, there is a considerable
increase in the range of production values and thus tropical water bodies offer better
opportunities for extensive and semi-intensive cage and pen culture (Le Cren and Lowe-
McConnell,1980).
Despite the favorable conditions in most parts of the continent, the contribution of Africa to
global aquaculture products is low and the contribution of sub Saharan African (sSA)
counties are very low. The contribution of Africa to global aquaculture products is less than
1% and the contribution of sSA in 2003 was a mere 13.6 percent to the African total or 0.13
percent of the world total (FAO, 2006; FISHSTAT Plus, 2005). However, in Africa
aquaculture production has increasing as increasing world aquaculture production. Although
Africa contributed less than 1 percent to global aquaculture production (251 000 t in 1999)
the production has been expanding since 1984 at a rate equal to or greater than the global rate,
albeit from a muchsmallerbase (FAO,1997).
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