The Effect of pH on the Fry Sex Ratio

The Effect of pH on the Fry Sex Ratio

Written by George J. Reclos Friday, 07 December 2001 01:00

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It has always been a rather controversial issue. It is generally accepted that water parameters do not influence the sex of the fry of African cichlids from Lake Malawi or (at best) they influence it only in some particular species. Lately, in TFH (November 2000 issue) I read a response by Mr. Boruchowitz (a man with much experience in keeping, breeding and raising African Rift Lake cichlids) who said exactly that. "Temperature" he said "does not influence the sex ratio" while "water parameters (pH in particular) has been reported to affect the sex ratio in dwarf cichlids although this is very species - specific". 

This may well not be so. I have been raising fry just for the fun of it and I have been lucky enough to have spawned many species till now. While still a newbie I didn't care that much about water parameters and I merely tested my water regularly to see if there were any fluctuations that might harm my fish. My fish, happily enough, went on spawning regularly and I was raising the fry. The water parameters were pH=7.6, GH=8 and KH=10. Temperature did vary in the summer months, sometimes exceeding 30 degrees C, NH3, NO2 and NO3 not detectable (keeping my Africans in a heavily planted tank, I never had a problem with nitrates), see Table below. When my haps and mbuna started to show their semi-adult colours I was surprised to see that I got very few males. I attributed this finding to the fact that all my fish were relatively young and kept on the same water parameters. This went on for several months the sex ratios being very much female biased. At best, I would get 15% males. I made sure that I didn't have any submissive males in my tanks by removing the males which had already coloured but the figure was always the same. Not more than 15% males with a massive 85+% of my fry being females. This posed two problems to me. The first had to do with selling the fish. While with mbuna or haps that had "coloured" females there was no problem, with species like Sciaenochromis fryeri and Cynotilapia mbamba this was definitely a problem. Secondly, I wanted to have a good number of males to select the ones I would to keep as successors to the ones I had.

I then read an article about Discus (Symphysodon discus) explaining why the discus can't have fry in alkaline hard water. The reason was that the salts didn't allow the sperm to penetrate the eggs which were too hard for them. This was an evidence that water parameters had something to do with fertilization. I also knew that in humans, the "Y" sperm (which will give males) lives a shorter life but is much faster in its moves so it will reach the egg first. Combining these two observations I concluded that the water parameters I had could possibly allow the "female" sperm to penetrate and fertilize the eggs easier than the "male" one. I was sure that temperature should not play a role on it, let alone the fact that I could do nothing about it (buying a chiller was financially out of the question). I decided to change the water parameters by adding a salt mixture that would a) raise the pH to the 8+ region (8.3-8.4 regarded as the optimum) b) make sure that this mixture would have a great buffering capacity so the environment would be pretty stable and c) make sure that the elements to be added in my tanks were as close to the chemistry of their natural habitat as possible. Lake Malawi is reported to have a very high percent of silicates for which I could do nothing. I just added tons of sand in my tank (silicon dioxide) so, if any dissolution would ever occur it would be beneficial. I also added Magnesium, Calcium, Potassium (while keeping sodium concentration much lower than before), Chlorine (as chloride ions of course), Iodine (trace quantities), sulfates and of course, generous amounts of carbonates. The pH was at 8.3-8.4 all the time (with regular 25% weekly water changes), the GH was constantly 12 and the KH rose to 15. 

Well, after a while all the fish started spawning. I mean ALL the fish ! In order to have some measure of comparison, I selected to save and raise broods from the pairs I had already raised broods previously. One of my biggest problems was with Sciaenochromis fryeri whose females are colourless while the males have the most striking blue amongst freshwater fish. Six months after the fry was released by their mother I knew I was right. Although only faintly colored I could count six males out of 24 fishes. In the end I did have 15 males (an astounding performance when compared to a mere 4% with the previous parameters), see Table below. The same pair spawned twice since then (even in the summer - so definitely temperature doesn't influence the sex ratio; only the carrying period is considerably shortened) and the average males were 57% of the brood. The same was true with Melanochromis chipokae (same pair) and Labidochromis caeruleus (I am not sure if it was the same pair - the female was the same). Cyrtocara moorii broods were also male biased to a great extent (more than 80%) but I didn't keep that species with the old parameters so I don't know if the sex ratio was really altered. My Italian friend, Francesco, sent me a trio of F3 Haplochromis (Pundamilia) nyererei. I introduced them in my tanks with the new water parameters and soon they spawned. You can imagine my pleasure when I saw that less than 15% of the total brood were females. Watching these bright red top guys swimming in my tanks made me a really proud fish keeper. Of course later nature taught me a lesson, the tough way.. These guys are not meant to be crowded. They just kill each other and you have to keep them as few as possible per tank. Which raises the question: is it normal or even ethical to bias the sex ratio?

Firstly, I do not know if actually this is a rock solid finding. If it is, then the answer is that probably we need to search the conditions at which a 50-50 sex ratio would be obtained. Perhaps in nature more males or females are needed because of the ecosystem which allows more fish from one sex to reach maturity so the sex ratio is biased towards the weaker one.

Secondly, I don't know if it is the pH alone or its combination with the specific salts I used. Third, and most important, these values are very close to the concentration of the same ions found in their natural habitat so I don't feel like playing God. A question may be posed on this particular Lake Victoria cichlid which probably needs less males / brood.

Fish keeping is a rather expensive hobby, especially if you try to do it the correct way - without compromises. Raising fry that will allow you to get some money - which will eventually be reinvested in your hobby - is not trading, not to me. With haps, it is a rule that the males sell, while the females are just a necessary bi-product. If this technique allows the serious and conscious hobbyist to make his life (and his fish lives) better then I hope this article will help. 

This article has first appeared in FAMA, April 2001.