Woodhouse, C. W.

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THE FISH IN LAKE MAGADI
THE FISH IN LAKE MAGADI
By C. W. WOODHOUSE
95
In the shallowsodaspringswhichfeedLake Magadithere
are foundsomesmallfishwhichhavebeenidentifiedby Mr.
Boulengerof the British Museumas Tilapia m08sambwa.
They werediscov.eredby Mr. F. W. Grahamandwerestated
by Mr. Boulengerto be immature.
Thesefishwereobservedand studiedagainin the month
of December1911,by the presentwriter,and werefoundat
that time to be breeding,ova and fry in all stagesof
developmentbeingsecured.
Thehabitatof thesefishis interesting.
Lake Magadiis situatedin a depressionof the Rift Valley
at an altitudeof about 2,000ft. The surroundingcountry
is arid andwaterlessfor a longway on eachsideof the lake.
The nearestactualwateris the SouthernGuasoNyiro River
situatedon the westof the lake,somefifteenmilesfrom the
springson the eastsideof the lakewherethe fishoccur.
The springson the east side comeout from under the
cliffswhichsurroundthelakeandflowoverthesilicaandinto
the motherliquor of the sodaitself. This water is highly
chargedwith sodaandaveragesa depthof fromoneto three
inches. The fish appearto congregateas nearthe origin of
the wateras possible,althoughthey are not averseto going
somewaydowntowardsthesodaitself.
Thecompositionof thewateris asfollows:-
The solidsare principallysodiumcarbonatewith traces
of magnesiumcarbonate, sodium chloride and sodium
bicarbonate. Shadetemperature,9.30A.M., 92°F.
It is a physicalimpossibilityfor the first occurrenceof
thesefishto havebeenwater-borne,astheirsituationin regard
to the neighbouringcountry precludesthis,unlessthey are
survivors(whohavetakento shallowwater)of theperiodwhen
Lake MagadiwasnQtsolidor comparativelyso. Shouldthis
be the case,they will probablybefound to have developed
localvariations.
VOL.!I.-No.4. H
THE FISH IN LAKE MAGADI
The moreprobabletheory of their introduotionmay be
takenthatsomeovaadheredto thebillsor legsof someof the
pelicans,flamingoesor duck which frequentthe lake. And
fromthis start they haveincreasedandmultiplied.
Theirhabitsarebrieflyasfollows:-
The malesappearto be greatlyin excessof the females.
The malesmay be readilyrecognisedwhensexuallymature
by their brighter colouring,iridescence,the white of the
lower lip morepronounced,absenceof verticalbarring,and
usuallybytheirlargersize.
Thefemaleis dullerin colouring,barredvertically,andwhen
gravid considerablyswollen,usually fewer in number and
smallerin size.
A primitivenestis preparedfor the receptionof the ova
in the sandy mud. The work appearsto be done entirely
by the male,but the placespreparedappearedto beusedby
manydifferentindividuals.
A maleselectsa favourablespot,oftenneara largestone.
A spaceof somethreeinchesacrossis diligentlycleanedof
obstructions,suchas the greenalgre-likegrowth that coats
thebottomof thesprings,smallstones,&c. Thesearemoved
by the maletaking eacharticlein his mouthand depositing
it on the edgesof the depressionthus caused. Whenthis is
finished,oneor morefemalesdeposittheirovawhicharelater
fertilizedby the male.' The processappearsto be similarto
thatemployedby otherfish,theabdomenbeingpressedagainst
the bed of the nest,the fish propellingitself forwardat the
sametime. After the operation,otherfishappearto deposit
their ovaand milt. Variousmalesappearto keepa cursory
guardoverthenest,drivingawayotherfishin theneighbour-
hood,but longbeforethe fish arehatchedthe males'interest
in thenestappearsto evaporate. Theovaarespeeq.ilycovered
withthegreenvegetabledepositanddisappear. As soonasthe
fishstartto hatchthereis a rushof all the neighbouringfish,
andasmanyalevinsandovaascanbefoundaredevouredby
the adults. The greaterportionof the specimensof alevins
collectedwere from the stomachsof fish engagedin thus
robbingnests. Thosethatescapethecannibalisticpropensities
of theirrelativeshidethemselvesin the algre. On absorption
THE WATER-ELEPHANT 97
of theyolk-sacktheymoveinto theshallowestwaterpossible,
from oneto half an inch in depth.
After passingthroughthe fry stage,the slightly bigger
fish betakethemselvesto the reedsand grassgrowingin the
springsandwhennearlyadultcomeoutintotheopenandmove
aboutwith theshoals.
Theirfood,besidesovaandfry, appearsto consistof water
fleas(Cyclops)andvegetablema.tter. Therebeinga very large
numberoffishin eachspring,foodmaterialisapparentlysoarce.
This fact and the restrictedareaof their habitat appear
to accountfor the fact of their stuntedgrowth,three to
threeandahalfinchesbeinganexceptionallylargefish. Their
adaptabilityto the strength(in soda)andtemperatureof the
wateris alsoworthyof note.
In conclusion,everycredit is due to Mr. F. W. Graham
whofirstbroughttheoccurrenceof thesefishto notioe.
THE WATER-ELEPHANT
By R. J. CUNINGHAME
M. Le Petit, whois at presentin Nairobi,wasfor a period
of fiveyearstravellingin theFrenchCongo,and:hehaskindly
furnishedmewith a somewhatdetailedaccountof theWater-
Elephant.
The first timehe sawonewasthreeanda half yearsago
(about June 1907)whentravellingdown the River Comgo,
nearthejunctionof theRiver Kassaiwith theRiver Congo.
The secondoccasionwasin the swampycountrybetween
Lake Leopold II and Lake Tumbanearto wherethe M'fini
River findsits exit from Lake LeopoldII. This is in what
is knownas the LukenyeDistrict.
His first viewof a water-elephantwasthat of a headand
neckonly,at Someconsiderabledistance,appearingabovethe
surfaceof thewater; andhe,beinginaboatornative' dug-out
canoe,'thought it was a big tree-snag. The nativeswith
him told him it wasa.water-elephant,andshortlyafterwards
n2


Fish in lake Magadi

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Fish in lake Magadi

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