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Cichlid Sex Determination Research
at the University of Michigan
By Ronald George Oldfield with photos by the author
University of Michigan Museum of Zoology, 1109 Geddes Ave.,Ann Arbor, MI 48109, [email protected]
When I was first notified that I had received the Guy Jordan Award, I was immediately excited about
an opportunity to write an article for the Buntbarsche Bulletin. In addition to describing the research
that I accomplished with the funds, I would also like to take the opportunity to describe how the cichlid hobby has affected both my professional and personal development.
My passion for fishes began when I won several goldfish in the ‘ping-pong ball toss’ game at the
Lenawee County Fair in Adrian, Michigan when I was 6 years old. I have kept fish as pets ever since
that time except for two intervals, each lasting a couple of years, where I kept reptiles and amphibians instead. By the time I was in my early teens I had become fascinated with cichlids, especially
Amphilophus citrinellus, Lake Nicaragua
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Central Americans. I didn’t buy many fish books, but I bought and memorized the available books by
David Sands (Sands 1983) and Ad Konings (Konings 1989). I even gave a presentation with a live
‘Cichlasoma’ trimaculatum for a public speaking course in high school. It was hard to get very deep
into the hobby, as there were no hobbyist clubs in the area where I grew up. However, I was always
heavily involved in keeping fish, and before I had finished high school I had secured a job in a pet shop,
Brentwood’s Pet Ranch, in Adrian, Michigan.
Soon after I graduated from high school I landed a job managing the aquarium room at another pet shop, the Aquarium Center, in Toledo, Ohio. Having this job and living in a larger city allowed
me to dive deeper into the hobby, but there were still no local clubs, and I had little idea what was
going on in the worlds of hard-core cichlid keeping or professional study. Dismayed by the financial
outlook of my retail position, I moved into other fields and spent the next six years working a number of diverse jobs. Although I enjoyed most of the positions I held, each one of them left me with an
empty feeling, as though something were missing. When I was 24 I took on student loans and enrolled
at the University of Toledo. This school had virtually no ichthyological component. However, it did
open doors for me to gain experience working with various aspects of aquatic biology of Lake Erie,
as well as experience at the Toledo Zoo aquarium and the Bowling Green State University Marine
Biology Lab. While I was in college I put forth serious effort and earned a
good grade point average. By this time I was attending conventions held
by the Ohio Cichlid Association and the American Cichlid Association.
My good GPA and GRE scores, combined with my enthusiasm, landed me a position in the Master’s program in Biology at the University of
Michigan. I knew that Dr. Robert Rush Miller had worked there and that
he had a history with Central American cichlids, and it was nearby. It
seemed fitting that I enroll there. The following year I transferred into the
Ph.D. program, and then was on a path to doing some real cichlid research.
When I had established my position in the Fish Division in the Museum of
Zoology I was in cichlid heaven! The resources were staggering. I dove
into the nearly complete collection of cichlid literature. I had access
to a specimen collection that included most species of Central American
cichlids. In addition, there was a huge aquarium room at my disposal.
Phylogenetics (the study of evolutionary relationships) is the central
focus of the Museum. I had always been intrigued by the diversity of Central
American cichlids, and although I had had little training in evolutionary
biology, I had pondered their possible histories. I considered going down this
road of study. I found it very interesting, but I liked live fishes! How do they
develop? How do they communicate? Why are they so aggressive in small
aquaria? These questions hounded me. I had read the article by Ron
Coleman in Cichlid News (1997) that described the finding by Francis and
Barlow (1993) that Midas cichlids, Amphilophus citrinellus, have sex
determined not by genetics but by behavioral interactions and I felt
compelled to know more about it.
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At this point my literature investigations began to take focus. I found other reports of sexual
lability in cichlids. Interestingly, some cichlids have sex determined genetically, some have sex determined by temperature and/or pH, and at least one is apparently capable of changing sex as an adult
(reviewed by Leibel 2002). To me, this co-occurrence of different expressions of sexual development
all in one family of fishes seemed to provide a hint as to how sexual lability might evolve.
Sequential hermaphroditism, which is adult transformation from a functional male or female to
the opposite sex, is not unusual in coral reef fishes and has been the subject of much research. Early
on it was noticed that even many non-hermaphroditic fishes actually undergo sex changes when
very young. In these species all individuals initially differentiate as females, then at an early stage of
development the ovaries of presumably genetic males begin to transform into testes. This is really
not as strange as it may seem. Something similar happens in humans. All humans begin differentiating as females. Male development begins later, hence the presence of nipples on men. These
observations suggested that a change in developmental timing – a delay of this sex change from
the larval stage to adulthood – might make sequential hermaphroditism possible (Atz 1964). In the
late 1980’s and early 1990’s investigations of development in sequential hermaphrodites provided
evidence that supported this hypothesis (Shapiro 1987, Francis 1992). The diversity of developmental patterns in cichlids is consistent with these findings. Cichlids are the only family of fishes
known to undergo sex determination at four distinct life stages: some undergo genetic sex determination and are not labile, some have sex determined by pH or temperature at the fry stage, the
Midas cichlid has sex determined by behavioral interactions at the juvenile stage, and Crenicara
punctulata undergoes behaviorally controlled sequential hermaphroditism. This continuum
indicates that sequential hermaphroditism, as well as the other forms of sexual lability, evolves by
a change in developmental timing. This interpretation led to a review paper that eventually
became my first scientific publication (Oldfield 2005).
I convinced the University of Michigan faculty that sex determination in cichlids was an
interesting topic, and that it may lead to a better understanding of the evolution of sexual lability in
other fishes, but there were still other hurdles to overcome. Since Dr. Miller retired, the condition of
the aquarium room had steadily declined, and a year after I took residence in the Museum it failed
to pass inspection and was decommissioned by the University Committee on Use and Care of
Animals. Unfortunately, although Dr. Miller was still alive when I came to the Museum, his health had
deteriorated to the point that he could no longer come in. Bob was in a nursing home and although
my advisor, Dr. Gerald Smith, expressed desire to introduce us, he wouldn’t do it in the condition Bob
was in. Bob passed away about a year later. He was the driving force behind the aquarium room, and
without his involvement it had slowly degenerated. When I got there it was in terrible shape. Now I
had another problem. In addition to getting money to cover the costs of field work in Nicaragua and
laboratory expenses, I also had to somehow find the money and time to renovate this room—a
daunting task.
I am not one that believes in fate, but I sure am lucky I study cichlids. The money provided by
the ACA allowed me to pay for the aquarium room renovation. If a graduate student in cell or molecular biology accepted a position in a lab and was told that he had to paint the floor before he could
begin research he would laugh in their faces and walk out. Well, that’s not the way it works in zoology.
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Dedicated hobbyists and the
well-organized state of the cichlid
hobby made it possible to obtain live
Amphilophus specimens of known localities. Top: A. citrinellus ‘red head’, Costa
Rica. Right: A. zaliosus, Lake Apoyo.
After two years of painting aquarium racks and the floor, updating
light fixtures, and throwing away
dozens of ancient metal-rimmed
and granite aquaria, Heetmaster
heaters, and other artifacts, I was
finally able to purchase new supplies and got the room re-commissioned. The result is a laboratory
ideal for maintaining fishes and other aquatic organisms. The room contains over 200 aquaria ranging in size from 1 to 250 gallons. Suspended from the ceiling and plumbed into the building’s water
supply there is a 500 gallon reservoir that is used to age tap water. Lines from the reservoir run above
the aquarium racks so there is easy access to freshwater for water changes, and several floor drains
throughout the room allow easy draining of aquaria. The room is on the top floor of the Museum,
and several skylights allow illumination with natural sunlight.
Surprisingly, the preliminary experiment that I ran in a smaller lab failed to corroborate the
results of Francis and Barlow (1993). Their experiments had concluded that individuals that are large
relative to their group-mates develop as males, and those smaller as females. My first experiment
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Four aisles, each two or three shelves deep with aquaria, hold over 200 small aquaria, most of which are
5, 10, 20, 29, or 50 gallons. Airlines and waterlines from the reservoir run above the aisles.
failed to find a strong association between size and sex in sub-adult fish. However, with the large space
newly available in the renovated aquarium room, I am now replicating the experiment while
manipulating factors like group size, which can profoundly influence social structure in juvenile Midas
cichlids (Oldfield, unpublished data), and locality of origin, which is especially important now that
Midas cichlids are thought to consist of up to 20 different species in the different crater lakes of
Nicaragua (McKaye et al. 2002).
In addition, the large space provided by the aquarium room has allowed for a detailed investigation of gonadal development in the Midas cichlid. In this experiment 105 aquaria were used to raise
fish under different social conditions. Juveniles were sampled once per week for three months. This
will provide a streaming picture of the changes that occur in the gonads as the fish mature. If the
experiments corroborate the findings of Francis and Barlow (1993), then the hypothesis proposed in
my review paper will be supported. If Midas cichlids turn out not to be sexually labile, then behavioral interactions may still influence timing of sexual development (this has been reported in other
cichlids). If this is the case, it may explain how processes in behavior and physiology can evolve to
control sex change in sequential hermaphrodites: they already exist! Behaviors likely control proportions of male and female gonadal tissue, even in non-sex-changing fishes. These processes may then
be co-opted to control sex change when a mutation results in an extended period of gonad lability.
It has been a privilege to work in the lab of such a famous ichthyologist as Bob Miller. His legacy
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There are also larger aquaria, up to 100, 110, and 250 gallons.
lives on in the Museum. The literature and specimen resources that he left behind continue to draw
cichlid biologists to the institution. In 2002 the Fish Division graduated Dr. John Sparks who combined
morphological and molecular characters to hypothesize a phylogenetic and geographic history of the
cichlid fishes, with a focus on Madagascar and Indian species (Sparks 2004). His evidence indicated
that these two groups are more closely related to each other than either was to other cichlid groups,
and that together they are sister to all of the other cichlids. The African and Neotropical species, also,
were each more similar to others from the same continent than they were to species from other continents. The relationships indicated that cichlids attained their current geographical distributions because
they originally existed on one ancient landmass, Gondwana, and were separated when it broke apart
into today’s continents, rather than by ‘island hopping,’ or swimming through the ocean, as had been
proposed previously. The following year Dr. Josh Trapani graduated. Josh studied body shape and the
development of pharyngeal teeth in an attempt to better understand the dimorphisms present in the
Cuatro Cinégas cichlid Herichthys minckleyi (Trapani 2003). He found that fish with papilliform teeth do
not differ significantly in size or shape from those with morariform teeth, but that they exhibit different
patterns of body-form variability. Within each dental morph, body shapes include ‘piscivores’ and
‘deeper-bodied dietary generalists.’ However, fish with papilliform teeth show a continuous distribution
between the two shapes, whereas molariform fish lack individuals with intermediate body shapes.
Last year we were privileged to host the president of the Mexican Ichythological Society, Dr.
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Above left: The lab houses a wide range of aquaria. Above right: A reservoir of approximately 500 gallons
suspended from the ceiling is used to age tap water.
Juan Schmitter-Soto, for a year-long sabbatical as he worked on a revision of the genus Archocentrus.
He identified many previously unrecognized strains of convicts and Jack Dempseys (Schmitter-Soto
2005). My fellow Ph.D. student and officemate, Prosanta Chakrabarty, has been taking an approach
similar to John Sparks to understand the evolutionary history and geography of the Antillean cichlids
of the genus Nandopsis. He also recently published results of a body shape analysis that found that
there is more variability in shape among Tanganyika cichlids than Malawi cichlids, more variability
among piscivorous cichlids than cichlids with other diets, and that disparity of the head region was
greater than that of the rest of the body (Chakrabarty 2005). Finally, Peter Esselman has developed a
proposal for a large-scale ecological model that will predict the consequences of future tilapia introductions on the cichlids and other fishes native to Belize, Honduras, and northeastern Mexico.
No setting could have been better for me and my cichlid fascination than the University of
Michigan Museum of Zoology, but I have also remained active in the hobby. The resources of the
University helped me to found the Aquarium Society of Ann Arbor, which has now been functioning
for two years. This organization provides a forum that facilitates interactions among people in different fields who are all interested in fish. Evolutionary biologists from the museum, fisheries biologists
from University of Michigan’s School of Natural Resources and government agencies, and public
aquarists and hobbyists all meet to discuss fish. The club has also hosted many high-profile speakers
in a setting that is accessible to the public as well as the University community.
The state of the cichlid hobby is ultimately responsible for facilitating the accomplishments that
I am currently making. In addition to the aid of the American Cichlid Association, the dedication and
organization of advanced cichlid hobbyists has enabled a more complete approach to my research.
I was presented with a particular problem when trying to obtain live Midas cichlids from diverse local-
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ities, a task that would entail an impractical amount of field collecting. Museums only maintain preserved specimens. Knowing that one of the stated primary goals of zoos and public aquaria is conservation, I contacted many that I knew maintained Amphilophus spp. To my dismay some didn’t even
respond to my inquiries. Those that did informed me that the specimens they maintained were either
hybrids or pond-raised fish from the pet trade. Not exactly what you would expect from institutions
dedicated to conservation and research. Luckily, because of my connections in the cichlid hobby, I
was able to obtain Amphilophus spp. from Jeff Rapps at “Tangled Up in Cichlids” that were offspring
of fish collected by hobbyists such as Willem Heijns and Bob Rawlings who had recorded the locations of their collections. Long live the cichlid hobby!
Literature Cited
Atz, J.A. (1964) Intersexuality in fishes. In: Intersexuality (eds. C.N. Armstrong and A.J. Marshall). Academic Press,
London, pp. 145-232.
Chakrabarty, P. (2005) Testing conjectures about morphological diversity in cichlids of Lakes Malawi and
Tanganyika. Copeia. 2005: 259-273.
Coleman, R. (1997) Cichlids and science: Sex determination. Cichlid News. 6: 20-21.
Francis, R.C. (1992) Sexual lability in teleosts: developmental factors. The Quarterly Review of Biology. 67: 1-18.
Francis, R.C. and Barlow, G.W. (1993) Social control of primary sex differentiation in the Midas cichlid. Proceedings
of the National Academy of Science USA. 90: 10673 – 10675.
Konings, A. (1989) Cichlids from Central America. TFH Publications. Neptune, NJ.
Leibel, W. (2002) Cichlidist’s library. Buntbarsche Bulletin. 4: 24-28.
McKaye, K.R., Stauffer, J.R. Jr., van den Berghe, E.P., Vivas, R., Lopez Perez, L.J., McCrary, J.K, Waid, R., Konings,
A., Lee, W., and Kocher, T.D. (2002) Behavioral, morphological, and genetic evidence of divergence of the Midas
cichlid species complex in two Nicaraguan crater lakes. Cuadernos de Investigacion de la U.C.A. 12: 19-47.
Oldfield, R.G. (2005) Genetic, abiotic and social influences on sex differentiation in
cichlid fishes and the evolution of sequential hermaphroditism. Fish and Fisheries. 6: 93-110.
Sands, D. (1987) Fishkeepers Guide to Central American Cichlids. Tetra Press. Blacksburg, VA.
Schmitter-Soto, J.J. (2005) A systematic revision of the genus Archocentrus (Teleostei: Cichlidae), with the description of two new genera and six new species. Zootaxa. In press.
Shapiro, D.Y. (1987) Differentiation and evolution of sex change in fishes. Bioscience. 37: 490-497.
Sparks, J.S. (2004) Molecular phylogeny and biogeography of the Malagasy and South Asian cichlids (Teleostei:
Perciformes: Cichlidae). Molecular Phylogenetics and Evolution. 30: 599-614.
Trapani, J. (2004) Geometric morphometric analysis of body-form variability in Cichlasoma minckleyi, the Cuatro
Ciénegas cichlid. Environmental Biology of Fishes. 68: 357-369.
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