THE ROLE OF ORAL INCUBATION IN THE EMBRYONIC SURVIVAL OF THE CICHLID FISH, TILAPIA MACROCEPHALA (BLEEKER)

149 Pages·4.028 MB·English

by  SHAW, EVELYN S

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LD3907 1 3 - i l V I 8 s
£o?2 aliaw, Evelyn &•, 19^7- *
- "The ro le of o ral incubation in tl»
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eirbryonic survival o f the C ichlid
fish , T ilap ia m acrocephala (Bleekei}
6Cp. illu s ., diagrs*, tables*
Ihesis ’rh*D*) - K.Y.U., Graduate
v.chool, 1952*
B ibliography: p ,78-88*
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Xerox University Microfilms, Ann Arbor, Michigan 48106
THIS DISSERTATION HAS BEEN MICROFILMED EXACTLY AS RECEIVED.
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UNIVERSITY H’ElUWW'
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THE ROLE OF ORAL SiGORkTICM IN THE EMBRXCNIC SURVIVAL
OF THE CICHLID FISH, THAPIA MSCRflCRPmiLA (BLEEKER)
Evelyn S. Shav
A dissertation in the Department of Biology submitted to the
faculty of the Graduate School of Arts and Science of Nev Xork
University in the partial fulfillment of the requirements for
the degree of Doctor of Philosophy,
1 9 5 2
T A B L E OF C O N T E N T S
Page
INTRODUCTION AND ACKN CWIEDGMBNTS.............................................................. 1
REVIEW OF THE LITERATURE .......................................................................... 6
MATERIALS AND METHODS.............................................................................. 11
Maintenance of adult fish . . . . . . . . . . . . . . . H
Method of obtaining embryos ......................... 12
Embryological studies ................. . . . . . . . . . . . . 12
Experimental s tu d ie s.............................................. 12
Experimental organization . . . . . . . . ......................... 13
RESULTS ............................................................................................................. 15
Embryology • • • ...................................... . . . . . . . . . . 15
Description of gametes ...................................................................... 15
F e rtilisa tio n ................................................................... . . . 16
Stages of embryonic development . . . . .......................... 16
Experimental studies 33
Survival in the adult's oral cavity 33
Extra-oral embryonic survival in aquarium water . . . 34-
Survival in sea water d ilu tio n s................................................. 34
Investigation of ionic factors........................................................ 36
Investigation of osmotic factors . . . . . . . . . . . 42
Investigation of bacteriacidal and fungicidal factors 43
Page
Investigation of mechanical facto rs................................. 57
Investigation of the oral cavity . . . . . . . . . . 63
DISCUSSION................................................................................................. 71
SUMMARY AND CONCLUSIONS.................................................. 77
BIBLIOGRAPHY............................................................................................. 78
I N T R O D U C T I O N
"This same fish ^Geophagug7 has a most extraordinary
mode of reproduction. The eggs pass, I know not how, into
the mouthy the bottom of which is lined by them, between
the inner appendages of the branchial arches, and espec­
ially into a pouchy formed by the upper pharyngials, which
they completely fill. There they are hatched and the
little ones y freed from the egg case y are developed until
they are in a condition to provide for their own existence."
Thus wrote Louis Agassiz in 1868 to his colleague, Professor Milne
Edwards t of the Jardin des Plantes. Since the time of Agassiz y mouth-
breeding has been a subject of particular Interest to a querists and
biologists. This unusual mode of parental behavior has been discovered
in several unrelated teleost families. Among these is the family
Cichlidae in which many species of several genera have developed var­
ious modifications of oral incubation. Several detailed studies have
appeared an various aspects of oral incubation in cichlld fishes. In
thesey as well as in the plethora of popular aquarists* literature,
there is a tacit assumption that the mouthbreeding habit is primarily
an adaptation for protection of the embryos and young fry from predators.
No one f as far as could be ascertainedy has ever looked into the possi­
bility that mouthbreeding may be otherwise necessary to the survival
of the embryos.
2
Daring the coarse of extensive studies on reproduction in the
cichlid mouthbreeding fish, mscrocephala (Aronson, 1949; Aronson
and Holz-Tucker, 1950), it was found that when the embryos were removed
from the mouth and placed into aquarium water taken from the tank in
which the spawning had occurred, they did not survive for more than two
or three days. These observations strongly suggested that the mouth
serves an additional function, possibly a physiological one, necessary
for the survival of the embryos. Casual observations were made by
Baerends and Baerends-Van Roon (1950) who reported that when the eggs of
Tn »T>i» natalensis and Baplochromls wwitieninr were removed from the
female's mouth within a week after spawning, they died and soon became
moldy. The failure of eggs to develop outside the mouth of
strigieena was also noted by Seitz (1940).
Tn*nia macrocephala was considered appropriate for this study
of survival factors in oral incubation because it has proven to be a
surprisingly hardy laboratory animal, able to withstand the rigorous
conditions of aquarium life. The adults breed readily in captivity,
reproduce frequently during the entire year and are not markedly affected
by seasonal variations. The embryos, which are incubated mainly by the
male are readily removed from the mouth, are large and are easy to handle.
It was apparent, early in this study, that for an adequate
investigation of the survival value of oral incubation, a knowledge of
the early embryology of the species was necessary. The most useful method
of describing emibryological development*, when needed as a basis for experi­
mental research, is by the designation of stages which show gross morpho­
3
logical changes. Oppenheimer (1937) emphasized the value of this
technique as being superior to the older methods where the number of
somites or the time after fertilization are used as criteria for de­
scribing the degree of development. As Oppenheiaer observes} "The
chronological age of a teleostean embryo* expressed in hours or days,
does not represent its actual age* which varies according to conditions
of temperaturte, oxygen supply, etc. The precise state of development
of older embryos cannot be expressed In samite numbers, since this
varies, when compared with the differentiation of other organ systems,
In embryos salntained under different conditions and probably In
embryos differing In genetic constitution*" Recently, a great number
of experimental studies have been based on stages and there are now
available among the more widely used experimental animals reference
stages for the k illiflsh , Fondulus heteroclitus (Oppenheiaer 1937),
Platvpoecilus maculatus (TaVolga, 1949), the leopard fTog, Rana nlpiena
(Shomuay, 1940), the salamander, punctatum (Harrison, published
by Rugh, 1948) and the chick, Gallus domesticus (Hamburger and Hamilton
1951).
Cichlid fishes are fresh-water forms found in South America,
Central America, north through Mexico, In Africa and In southern Asia.
Several of the species are known to have a rather high salt tolerance.
For this reason, Norman (1931) and ltyers (1938) classify the cichlids as
members of the secondary division of fresh-water fishes which means that
they may behave like true fresh-water fishes, but are less sharply
restricted to fresh water. Otae species, Ttiewi* pllotlca. is known to
live In the estuaries of the Dead Sea (Stetaitz, 1951) and In other
places of high salt concentration. T-n«rH» aacrocephala is found in
Vest Africa from the Gold Coast to Nigeria. It is often taken in the
river estuaries and coastal lagoons (Boulanger, 1915; F.O. Otoabo,
personal communication) In which the salinity, at tines, approaches
that of sea water (Irvine, 1947).
Practically nothing is known about the reproductive habits
of aacrocephala in their natural habitat, but much inforaatian
is available concerning reproduction in this species in the confines of
laboratory aquaria (Aronson, 1949)* Aronson describes a rather involved
and lengthy courtship procedure during which an excavation or nest is
built in the substratum. The fenale deposits her eggs in this nest and
they are fertilised as the male slowly rubs his genital papilla over the
eggs. Within a minute, the eggs are drawn into the male's mouth (fig. 1).
Here they are incubated from 6 to 22 days—mean 13.8 days—during which
time they are almost continuously churned by the respiratory movements
of the adult. Hatching occurs in the mouth on the fifth or sixth day of
development. When the brood is released at the end of incubation, the
young are fully formed fish.
Ota the basis of the considerations discussed in this section,
a series of experiments were planned to investigate the role of oral
incubation in embryonic survival. The approach chosen was to raise the
embryos extra-orally and to relate the factors of extra-oral survival
with factors in the aillen of the oral cavity. To expedite this experi-
- 5 -
mental study, a brief description of embryology from fertilization to
hatching was projected.
A C K N O WL B D G ME N T S
The writer is indebted to Dr. Lester R. Aronson, Chairman of
the Department of Animal Behavior, of The American Museum of Natural
History, and of New York University for his encouragement and sponsor­
ship of this work and for his reading and criticism of the paper. Thanks
are extended to Dr. Charles M. Breder, of The American Museum of Natural
History, to Dr. Ross N igrelli of the New York Zoological Society and
of New York University, to Dr. Milan J. Kopac of New York University,
to Dr. Helen Simpson Vishniac of Queens College and Haskins Laboratories
and to Dr. Villiam N. Tavolga of the City College of New York, for their
helpful suggestions. I also wish to thank Miss Madeline Levy for her
assistance in some of the histological preparations, Mr. John Polo for
maintaining the large stocks of fish, Mr. Thane L. Bierwert, Chief of
the Division of Photography of The American Museum of Natural History,
for photographing the emhryological stages and Miss A. Schaefer and Mrs.
H.C. Englert for typing the manuscript.
This study was supported in part by a grant to Dr. Lester R.
Aronson from the Committee for Research in Problems of Sex, National
Research Council.