Venting Jack Dempseys

There are always going to be times when determining the gender of your cichlids is particularly difficult. If your fish are roughly the same age, the males will generally grow faster and become bigger much more quickly than the females. If you want a pair from your local fish store, a good method is to choose the biggest and the smallest few of the bunch and you will likely walk home with at least a couple of each sex, if not an even split. However, if you have fish obtained from different sources or of different ages, things are not quite that simple.

In this post, I’ll use the Jack Dempsey as an example, but the information extends to many other cichlids as well. Besides having a specific interest in sexing them, the choice of the Jack Dempsey for this explanation is because JDs have very obvious visual distinctions between genders, but at the same time exceptions, where these differences are more subtle. (My post titled EBJDs – Electric Blue Jack Dempseys! gives these differences if you are unfamiliar with them.) In addition to standard Jack Dempseys sometimes being hard to sex when the males are super-blue or the females are super-black, electric blue JDs are impossible to sex with the blue cheek spangling method because their cheeks don’t have the underlying black colour to provide contrast to the blue – their cheeks are all blue! Alternatively, a battered fish of any colour, with severely mauled fins, makes the comparative fin size, length & pointedness method impossible as well. In these cases, the most reliable method of telling the gender of your fish will be to vent. Venting is the process of netting your fish, removing it from water and examining its ventral region, that is, the underside of between the ventral fins and the anal fin where the fish’s bits and pieces are kept. This can be a bit of a scary process, and make no mistake, it’s stressful to your fish, but it is sometimes the only option.

The following photo helps to illustrate the exact position of some more common body parts of a fish…

If looking down on a fish that is upside-down, from head to tail you will see the following anatomy in this order:

  1. head
  2. pectoral fins (side of body)
  3. ventral fins (bottom of body)
  4. anal pore
  5. genital papilla
  6. anal fin
  7. caudal fin (tail)

So, how exactly do you tell the difference you ask? Well, it still takes a bit of practice to be sure, but generally speaking male fish will have genital papillae that are equal in size or smaller that their anal pores, where female fish will have genital papillae that are significantly larger than their anal pores, often looking like a large bubble rather than a small dot. The vent of a male is thin and oval-shaped, while the vent of a female is fat and triangular-shaped. It is much easier to vent if your fish are ready to mate, as fish in spawning condition will drop their bits and pieces in preparation. When viewed from the side, males’ will look like a small forward-pointing hook-like projection and females’ will be much larger, much more obvious in the form of a rear-pointing ovipositor or egg-laying tube. It can also be observed while venting that the two openings on a male will be spread slightly farther apart and will be distinct, while on a female, the openings are closer and tend to touch. There are a couple of fantastic articles with some great photo examples listed in the references below.

By way of my own example, I have photographed the ventral regions of my five Jack Dempsey specimens, two blue and three regular. All of these fish are of differing ages and sizes, so some differences are definitely apparent due to this fact, however, I have can say with some certainty that the three regular JDs are all female (by way of the cheek spangling method, which is quite pronounced on all three), while the smaller of the EBJDs is likely a male (by way of the comparative fin method in relation to his in-store tankmates at time of purchase). I was told the “rescue” EBJD was a male by the fellow who sold him to me, however, I cannot say for sure as the fins are badly mangled and so sexing by this method is inconclusive. The photos are all arranged so the head is on top and the tail on bottom, meaning the top dot is the anal pore and the bottom dot is the genital papilla in all cases. Let’s examine…

Fish #1 – immature JD female, 6-12 months old

Fish #2 – mature JD female, 1-2 years old

Fish #3 – mature JD female, 1-2 years old (and fat with eggs)

Fish #4 – young EBJD male?, 1-2 years old

Fish #5 – full-grown EBJD male?, ancient

So, you can see the bubble in the top three photos (female) and the smaller, less pronounced opening in the bottom two photos, which leads me to believe that the two EBJDs are indeed male. This was the intention, so hopefully this is correct!

Of one last note, it is necessary to mention that there are some species of cichlid, angelfish in particular, that are right near impossible to sex by either venting or comparing fins/colours. In this last case, the remaining option is what I like to call the “bulge method”. Though not foolproof, males will usually develop a (sometimes subtle) bulge near their crown known as a nuchal hump, while females will develop a bulge in their belly as they mature and become loaded with eggs. Of course overfed males will have a bulging belly and young males will have no hump on their heads, so this method is limited in its use. This is especially so since by the time you’ve been able to observe bulging foreheads and bellies, your pair is likely either about to or has already formed, spawned and is guarding eggs, at which point the distinction becomes obvious as mom guards the eggs while dad patrols and fights off intruders!


Revised: 2012-02-12
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