This morning we got an e-mail from Dr. Chung of Hong Kong asking if we knew anything about a rumoured Pomacanthus hybrid that was collected in East Africa. Before we could even hit the reply button, we received another e-mail from Red Heart King showing pictures of the said fish from Africa. Indeed it looks to be a hybrid, and if we are right, it is one involving P. imperator and P. semicirculatus. The fish is now with Dr. Chung of Hong Kong, making this the second Pomacanthus hybrid in his collection, both of which came from East Africa.
Identifying Pomcanthus in their juvenile stage can be a little bit tricky. Identifying hybrids in the juvenile stage is a whole different ball game. This particular hybrid looks to be of one between P. imperator and P. semicirculatus. In the juvenile form of the latter, the tails are entirely opaque by the time the fish reaches this size. Juveniles also do not have the bubble chain like markings on the anal fin, which is found extensively in P. imperator. The semi translucent tail, coupled with the evenly spaced bars, anal fin patterns and the hint of brown on the dorsal fin points toward P. imperator x P. semicirculatus as being a likely option.
To date we have seen photos of three different examples of these hybrids, all in their adult stage. In the juvenile stage, this is our first. There are definitely more examples floating around that we are not aware of for sure. What’s interesting is that these hybrids are so far almost entirely collected from East Africa, despite the two species being sympatric over a vast geographical range.
In East Africa, five known Pomacanthus hybrids are known to occur involving four main parent species. In the photo above, a breakdown of the individual hybrids can be seen. They are
– P. semicirculatus x P. chrysurus,
– P. semicirculatus x P. maculosus,
– P. maculosus x P. chrsurus,
– P. chrysurus x P. imperator and
– P. imperator x P. semicirculatus.
P. semicirculatus is the most promiscuous species and in East Africa, forms hybrids with three species. In at least one of them, namely P. semicirculatus x P. maculosus, hybrids are not rare and are regularly seen in the wild and in the trade. In basic combinatorics, the formula nCr can be used where “n” represents the four parent species and “r” for any two of the four. As it takes two species to hybridise, then 4C2=6 will result in six different hybrid permutations. That is assuming all species are compatible to begin with. So far we have seen five, and the only hybrid yet to be seen is P. maculosus x P. imperator.
*Note that these six permutations are of standard one way crosses. Offspring can appear differently if the male and females were to be switched between species. For example, a male P. semicirculatus crossing with a female P. maculosus may look very different from a female P. semicirculatus crossing with a male P. maculosus. However in both ways the offspring is still considered a hybrid of two species and so we take that as one out of six permutations from four species.
There is a likelihood that the last pairing between P. imperator and P. maculosus isn’t viable, but based on what we can see above, its existence is entirely plausible. Considering hybrids have been documented from all four species, even in the extremely rare P. imperator x P. chrysurus, there is a chance we might see one in the future. Perhaps if it were to exist it would be a result of an accidental fertilisation where sperm and eggs were to mix unintentionally.
As mentioned before, it is very curious why much of the hybridisation is documented in the East African coast despite the four species being sympatric over many other areas. P. semicirculatus and P. imperator for example, overlap in a huge range covering much of the Indo-pacific, including Japan and Australia as well as parts of the Indian Ocean including the Red Sea. P. maculosus and P. semicirculatus overlap in the Red Sea as well, but only in East Africa are the hybrids collected very regularly. Perhaps the geographic history between Indo-pacific and the Western Indian Ocean have something to do with this.
Lastly, such hybrids are extremely variable and can be very difficult to tell especially in the juvenile stage. Some change at a younger age, allowing for easy identification, while others hold on to juvenile coloration at sizes upwards of six inches. In hybrids of P. maculosus x P. semicirculatus, they often show up in a wide range of variations and at different sizes. These are the commonest and appear in at least half of all African imports in Asia.
Only time will tell if Dr. Chung’s suspected hybrid is indeed P. imperator x P. semicirculatus. It could very well not be a hybrid at all and just a funky patterned juvenile. Knowing him, we will surely be seeing more of the fish as it grows into adult hood.