Canadian Killifish Association
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Jim Robinson Canadian Killifish Association |
For the last 4 years since I first obtained Simpsonichthys flavicaudatus Hellner 2, I have had severe difficulties with biased sex ratios. It has been so skewed in favour of females that I have nearly lost them 3 times. The ratio I was getting was approximately 1:25, male to female. Fortunately, I had found a single male out of a spawn to continue the line. Consequently, I have been unable to distribute this magnificent animal into the hobby. However, because of the huge amount of females, the males did not last long. They literally spawned themselves to death and wasted away. I guess they died happy, though.
About 2 years ago there was a discussion on one of the killie mailing lists about this exact problem in Nothobranchius only there was an overabundance of males. One respondent stated that he had placed 2 fry of a species into individual tanks and grew them in this manner. He stated that he ended up with a higher percentage of females than he was previously getting. He had no empirical proof, but it seemed that way to him
I decided to try the same thing in the hopes of a more balanced sex ratio with the Simpsonichthys flavicaudatus Hellner 2. The biggest problem for me, though, was to get enough eggs in order to get fair test results. Finally, in the winter of 1998 I ended up with 5 groups consisting of 1 male and 25 females. I felt that this would be sufficient to do my experiment.
The theory behind all this, I'm assuming, is that the males, as they are developing, produce hormones which prevent more males from developing. Hence, when an entire spawn is grown together, the first male to develop produces a hormone causing the other fish in the spawn to become females. This can only happen because the sex of a newly hatched egg laying fry is not determined for up to a month. After this time the sex has been established and all the fry can be put back together. In this experiment, I gave the fry 6 weeks in isolation just to be sure.
A similar situation to this can be found with guppies. Although the sex of a guppy is determinate at birth, guppy breeders still attempt to separate males and females as soon as possible. Apparently, the males give off a hormone which stunts the growth of the females so the separation is necessary. I still remember trying to separate guppies at 1 day old using a magnifying glass and a flashlight. This is one of the reasons I am now working with killies and not guppies!
Other experiments have been performed concerning sex ratios of fish. B.E. Kynard noted that with the Atlantic silverside (Menida menida) sex determination of the fry was determined under the control of both genotype and temperature during a specific period of larval development. Uwe Romer, in his experiments with Apistogramma spp. found that higher temperatures usually resulted in a higher percentage of males and that higher pH values resulted in more females.
Both of these experiments dealt with the variable of temperature. Romer's experiment also dealt with pH. In the following experiment these variables have been controlled, along with all other foreseeable variables so that only the number of fry per container varied. Thus, hopefully, only this single variable would be tested.
The experiment itself was conducted from March 15 to May 1, 1999. Eggs from the 5 numbered groups, which were all collected at the same time, were all hatched at the same time using the same water. Fry from each group were separated into 500 l. and 1500 ml. containers.
Five fry were placed in each of the 750 ml. containers and 10 fry were placed in each of the 1500 ml. containers. In addition, half of the fry from each spawn were placed together in a 20 l. tank with the same water.
Any fry from each spawn not included in the experiment were also placed together in a 20 l. tank. These were also included at the end of the experiment as a mixed control group.
The temperature in all containers was kept at a constant 24 C. (75 F). Exactly half the water was changed every other day using the same water at the same temperature.
Every effort was made to keep all of the variables controlled. These variables included:
| #1 | same collection date |
|---|---|
| #2 | same hatch date |
| #3 | exact fry numbers |
| #4 | same water |
| #5 | same amounts of water |
| #6 | same water temperature |
| #7 | same amount of water in each change |
| #8 | same amounts of food |
| #9 | the spawning adults were all kept in the same sized tanks at constant temperature in a system that automatically changed water. |
To simplify:
| Contents | |
|---|---|
| Group 1 | a) -4 (750 ml) containers with 5 fry each |
| b) -2 (1500 ml) containers with 10 fry each | |
| c) -1 (20 l) aquarium with 40 fry in each | |
| Group 2 | a) -2 (750 ml) containers with 5 fry each |
| b) -1 (1500 ml) containers with 10 fry each | |
| c) -1 (20 l) aquarium with 20 fry in each | |
| Group 3 | a) -2 (750 ml) containers with 5 fry each |
| b) -1 (1500 ml) containers with 10 fry each | |
| c) -1 (20 l) aquarium with 20 fry in each | |
| Group 4 | a) -6 (750 ml) containers with 5 fry each |
| b) - 3(1500 ml) containers with 10 fry each | |
| c) -1 (20 l) aquarium with 60 fry in each | |
| Group 5 | a) -4 (750 ml) containers with 5 fry each |
| b) -2 (1500 ml) containers with 10 fry each | |
| c) -1 (20 l) aquarium with 40 fry in each | |
| All others | -1 (20 l) aquarium with 52 fry |
On May 2, all of the fry in the 750 ml containers from each of the numbered groups were placed into a 20 l tank to complete their growth. The fry in the 1500 ml tanks were also placed in 20 l tanks. The fry already in 20 l tanks were also moved to other 20 l tanks. To maintain identical conditions all tanks were placed on a central system which does automatic water changes and is held at an exact temperature of 25 C. (77 F).
The results were fascinating! With all of the extra attention these 'wee beasties' received, not even 1 single fry was lost. Absolutely zero mortality!
The results can be summarized thus:
| Numbers | Ratio | ||||
|---|---|---|---|---|---|
| Fry | Males | Females | |||
| Group 1 | a) | 20 | 7 | 13 | ~ 1:2 |
| b) | 20 | 5 | 15 | 1:3 | |
| c) | 40 | 5 | 35 | 1:7 | |
| Group 2 | a) | 10 | 4 | 6 | 2:3 |
| b) | 10 | 3 | 7 | ~ 1:2 | |
| c) | 20 | 1 | 19 | 1:19 | |
| Group 3 | a) | 20 | 6 | 14 | ~ 1:2 |
| b) | 20 | 5 | 15 | 1:3 | |
| c) | 40 | 3 | 37 | ~ 1:12 | |
| Group 4 | a) | 30 | 12 | 18 | 2:3 |
| b) | 30 | 8 | 22 | ~ 1:3 | |
| c) | 60 | 4 | 56 | ~ 1:14 | |
| Group 5 | a) | 20 | 8 | 12 | 2:3 |
| b) | 20 | 6 | 12 | 1:2 | |
| c) | 40 | 6 | 34 | ~ 1:6 | |
| Others | 52 | 4 | 48 | 1:12 | |
The average for all 5 groups kept in containers with 5 fry: a) 37 males, 62 females, Ratio: 1:2
The average for all 5 groups kept in containers with 10 fry: b) 27 males, 73 females, Ratio: 3:8
The average for all 5 groups kept in containers with half the fry c) 19 males, 181 females, Ratio: 1:9
The average of all others: 4 males, 48 females, Ratio: 1:12
As a point of interest, I repeated this same experiment with eggs from the same numbered groups from May1 to June 15. The only difference was the age of the original spawning groups of fish. It was important to do this second experiment simply because there are some species of fish that produce more of a certain sex when they are young and reverse this trend as they get older. The results were almost identical!
| Numbers | Ratio | ||||
|---|---|---|---|---|---|
| Fry | Males | Females | |||
| Numbers | Ratio | ||||
| Fry | Males | Females | |||
| Group 1 | a) | 20 | 7 | 13 | ~ 1:2 |
| b) | 20 | 5 | 15 | 1:3 | |
| c) | 40 | 4 | 36 | 1:8 | |
| Group 2 | a) | 10 | 4 | 6 | 2:3 |
| b) | 10 | 3 | 7 | ~ 1:2 | |
| c) | 20 | 2 | 18 | 1:9 | |
| Group 3 | a) | 20 | 6 | 14 | ~ 1:2 |
| b) | 20 | 5 | 15 | 1:3 | |
| c) | 40 | 3 | 37 | ~ 1:12 | |
| Group 4 | a) | 30 | 12 | 18 | 2:3 |
| b) | 30 | 10 | 20 | 1:2 | |
| c) | 60 | 6 | 54 | ~ 1:9 | |
| Group 5 | a) | 20 | 7 | 13 | 1:2 |
| b) | 20 | 5 | 15 | 1:3 | |
| c) | 40 | 4 | 36 | ~ 1:9 | |
| Others | 23 | 1 | 22 | 1:22 | |
The average for all 5 groups kept in containers with 5 fry: a) 36 males, 63 females, Ratio: ~ 3:5
The average for all 5 groups kept in containers with 10 fry: b) 29 males, 71 females, Ratio: ~ 3:7
The average for all 5 groups kept in containers with half the fry c) 19 males, 181 females, Ratio: ~ 1:9
The average of all others: 1 male, 22 females, Ratio: 1:22
It seems rather obvious from these results that, indeed, one can improve a terrible sex ratio by limiting the number of fry placed together for the first month of the fishes' life at least with this species. It does require a great deal of work and a large number of tanks and containers. However, for some fish, which have a history of skewed sex ratios, it may be the only way to ensure the survival of that species. It actually appears from this experiment that, the fewer the number of fry held in each container, the closer to equal the sex ratio. To generalize that this will work for all species is extremely dangerous. This experiment has proven only that sex ratios in this single species can be altered. We may, by the fact that this is a South American annual species of the genus Simpsonichthys, predict similar results for other Simpsonichthys species and possibly for other South American annuals, but even this is somewhat risky. However, based on these results, it would not be risky to say that this method may just work in balancing sex ratios and that, at the very least, it is a good starting point to try with other fish.
Obviously, the next step is to attempt this same experiment with Maratocoara lacortei and Campellolebias dorsimaculatus. Both of these fish have also given me considerable difficulty with skewed sex ratios. The difference being, I get far more males than females. I wonder if this experiment will work in reverse so that I get a larger number of females. Let's hope so, eh!
<soapbox mode on>. Remember, the more fish we can breed in captivity, the less fish we need to remove from their natural habitat. Also, at the rate 'civilization' is destroying the natural habitats, it is incumbent on each and every one of us to attempt to breed and distribute to ensure the survival of all species. A friend told me recently of a newly found species, Simpsonichthys marginatus, which is not even listed in 'A World of Killies' by Wildekamp or in 'Pearl Fishes' by Costa. Its natural habitat is gone. No more can be found. The original habitat is now an enormous rice plantation and the species is, at the very least, extirpated, if not extinct altogether. Collectors still can not find any new locations for this amazing fish. "Now you see it.now you don't!" <soapbox mode off>
It appears that there truly is 'nothing new in the world.' After publishing this article in the AKA's JAKA, I was speaking to my friend and famed fish keeper Rosario LaCorte (Maratecoara lacortei etc, etc, ...). He told me that he had discovered this little trick back in the 50's or 60's. Not only that, apparently a Russian gentleman had done the same thing in the late 60's or early 70's. Even though I felt somewhat 'crest fallen' over the fact that I was no longer either creative or original, I was still pleased to add my little bit to science. Dan Katz also made me feel better when he told me that it was the "first published hard data" that he had seen. Thanks Dan.
Although the author was able to duplicate his results with almost identical consequences, it would seem to be a much better result if others could use the same criteria / controls / parameters to confirm these findings. This has now been done by several other people.
A University of Toronto student named Smith was able to duplicate the author's results. He sent me a copy of his paper (for which he won some scientific award) and the results were nearly identical. The only apparent difference occurred with keeping the large groups together. His ratios expanded to 1 male to 43 females - 1: 43. I do not know if he published his findings.
Curt Smith, a fellow SAA aficionado, gentleman and close friend, has taken this experiment even farther than did I. He was having extreme difficulty getting any females at all from Leptolebias aureoguttatus. He took his final batch of newly hatched fry and placed 2 fry each in a series of half filled 1 gallon plastic containers. He changed only small quantities of water weekly (Leptolebias aureoguttatus do not like large water changes!!!) until they were sexable. His results ????? A perfect ratio of 1:1
Curt has continued his experimentation on other species as well. In speaking with Curt this morning (22/01/2003) he gave me a partial list of his successful experiments with his species with skewed sex ratios:
| Species | Results |
|---|---|
| Simpsonichthys picturatus | yielded a 1:2 ratio |
| Simpsonichthys similis | pairs |
| Simpsonichthys notatus | pairs |
| Austrolebias bellottii | pairs |
| ... and 'believe it or not' | |
| Aphyosemion australe | pairs |
| Aphyosemion elberti Foumbam | pairs |
I would be delighted to hear from any other SAA or Nothobranchius breeder who has tried this experiment and tracked the results. It is of little import to me whether your results verify or contradict my results. I will add them to the continuing list of experimental results. The only important thing here is the accumulation of hard data and knowledge.
TTFN, eh
Jim
© 2002-2003 Jim Robinson
Published with permission: South American Annuals study group