Mbuna capable of sex reversal, says study
Sex reversal in the shell-dwelling Lake Malawi cichlid Maylandia cf. livingstonii has been documented for the first time in a paper published in the most recent issue of the journal Copeia.Jay Stauffer and Renea Ruffing conducted a series of experiments to show that this species is capable of changing sex.
In the first set of experiments, the authors used tanks divided into two compartments by a sheet of clear Plexiglass, where they placed one male in one compartment and three females in another.
In the second set of experiments, the authors maintained six females in two tanks and seven females in another two tanks, all in the absence of any male fishes.
In the first set of experiments, one female developed male secondary characteristics usually seen only in dominant males, and then fertilized eggs produced by one of the remaining females in the experiment, resulting in three large broods of fry.
In the second set of experiments, one female each in the tanks that held six fish began to display male coloration and behaviour after two months. During the third month, a female in one of the tanks was observed to be holding eggs, releasing a brood of fry two weeks later.
The authors note that although their experiments showed sex reversal, further studies are needed to document whether sex reversal occurs in the wild.
For more information, see the paper: Stauffer, JR Jr and RA Ruffing (2008) Behaviorally induced sex reversal of Metriaclima cf. livingstoni (Cichlidae) from Lake Malawi. Copeia 2008, pp. 618–620.
Nomenclatural note: although the issue of whether the correct generic name to be used for this species should be Metriaclima or Maylandia remains contentious, strong evidence has been presented that the latter name is the correct one to use. We follow current databases (e.g. Catalog of Fishes) in using Maylandia.
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Heok Hee Ng: 25.9.2008Views: Read 2,029 times
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"From the paper:
“We initially identified the sex of all individuals by color and length of the pelvic fins; subsequently, we examined the urogenital openings to support our initial determination. We used the following observations of behavior to corroborate our use of secondary sexual characters. Fishes that we initially identified as males exhibited strong territorial behavior and were observed courting females. In some instances, spawning was directly observed, but in most cases, sex was determined by morphology, behavior, and mouth brooding. In no instances did we observe a fish that we identified as a male brooding eggs or fry. All females used in the experiments had been observed mouth brooding at least one batch of fry or eggs. Whenever a fish that we determined to be female was found to be holding eggs or fry, she was removed and placed in a separate tank until the fry were released. Each fish, which we identified as being a male, had exhibited territorial behavior and was the only fish identified as a male that was held in the same aquarium as a mouth-brooding female. Therefore, we concluded that all fish used were either functional males or females.”"
Date: Tuesday September 30th, 2008, 7:14 am
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 | Singapore-based ichthyologist Dr Heok Hee Ng is a leading expert on Asian catfishes and has described dozens of fish ranging from catfishes, to nandids and cyprinids. |
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"How was the sex of the fish confirmed prior to the experiment?"
Posted by: Graham Ramsay - 1 year, 1 month agoDate: Monday September 29th, 2008, 7:19 pm