A Definitive Key to Identify African Tiger Fish (Hydrocynus)

[fugupuff]

May I throw a few odd balls in there to be identified?

and the 2nd to last forskahlii picture I think is vittatus, just my opinion this is what I consider as forskhalii over the years, a smaller specie, slender body, and short jaw. but then also sometimes I wonder if there is sexual dimorphism in this specie as well. As I've seen goliaths with much longer face and soem with just shorter face.

 

[fugupuff]

I just realized that I have a lot of tigerfish photos obtained here and there...

what about these 2? I still have tons more...

 

[fugupuff]

tanzaniae or brevis? Next will the be juvenile pictures of this fish, this fish was raised by a good friend of mine from a young fish. This one is exciting....

 

[Chicxulub]

May I throw a few odd balls in there to be identified?

and the 2nd to last forskahlii picture I think is vittatus, just my opinion this is what I consider as forskhalii over the years, a smaller specie, slender body, and short jaw. but then also sometimes I wonder if there is sexual dimorphism in this specie as well. As I've seen goliaths with much longer face and soem with just shorter face.

View attachment 844492

Without knowing its collection point, I would call that fish vittatus. I acknowledge its possible that Hydrocynus cf. "forskahlii population E" could potentially have a colored upper lobe, but I have seen no evidence to indicate this.

This is why type localities are important, and why I posted the body dimension measurements. A very thin vittatus could very well be skinnier than a girthy forskahlii. The second to last forskahlii picture (we're talking about the one of the one caught fishing, right?) was caught in the Nile. It's a very large, thick individual but I still feel its a forskahlii. The people who caught it identified it as forskahlii, as well. There's not supposed to be vittatus in the Nile per the literature I've read, only fatf and batf.

There is also a considerable amount of variety among vittatus and forskahlii because there are four distinct genetic populations of vatf and two of fatf. These populations await descriptions as subspecies and until they are described, we can only call them vittatus or forskahlii without having any way to more closely attribute which population they are.

We must also allow for variation between individuals and among populations. Allopatric conspecifics can display wild local variation while still fitting species diagnostics.

I also would not be surprised if forskahlii, or even all of Hydrocynus, displayed sexual dimorphism. As I mentioned above, populations of H. vittatus in the Zambezi were found to in fact display sexual dimorphism.

View attachment 844493View attachment 844494I just realized that I have a lot of tigerfish photos obtained here and there...

what about these 2? I still have tons more...

The dead fish, honestly I can't tell from the picture. The second one I would call a member of the vittatus complex if not vatf sensu stricto.

tanzaniae or brevis? Next will the be juvenile pictures of this fish, this fish was raised by a good friend of mine from a young fish. This one is exciting....

View attachment 844495View attachment 844496

Very deep body; short, stout, deep head; very large adipose fin, 'dirty' color, very dark red lower lobe, poorly formed striping. It has a body depth ratio of 23.7%. Based on this evidence, I would call that fish H. brevis.

edit- Just realized I can make that picture much larger. I counted 48-49 LL scales, again, right in the range for brevis but too many for tanzaniae.

I'm very much looking forward to juvi pics of that fish.

 

[Chicxulub]

A note about the relationship of vittatus and tanzaniae:

It has been found that tanzaniae and the vittatus complex to be very closely aligned. It was found that "...gene phylogeny confirms the established morphological diversity of Hydrocynus and reveals the existence of five previously unknown lineages, with Hydrocynus tanzaniae sister to a clade comprising three previously unknown lineages (Groups B, C and D) and H. vittatus" (Goodier et al., 2011).

This would account for the similarities in both body structure and patterning that is found between tanzaniae and cf. vittatus. This is why I feel that so many fish that are called vatf and which appear to be 'washed out', grey, green white and blue 'vittatus' are in fact often tanzaniae.

 

[fugupuff]

now with all that said, how do we know they do not infact hybridize in the wild, also accounting for some variations.

A note about the relationship of vittatus and tanzaniae:

It has been found that tanzaniae and the vittatus complex to be very closely aligned. It was found that "...gene phylogeny confirms the established morphological diversity of Hydrocynus and reveals the existence of five previously unknown lineages, with Hydrocynus tanzaniae sister to a clade comprising three previously unknown lineages (Groups B, C and D) and H. vittatus" (Goodier et al., 2011).

This would account for the similarities in both body structure and patterning that is found between tanzaniae and cf. vittatus. This is why I feel that so many fish that are called vatf and which appear to be 'washed out', grey, green white and blue 'vittatus' are in fact often tanzaniae.

 

[Chicxulub]

now with all that said, how do we know they do not infact hybridize in the wild, also accounting for some variations.

Excellent point, Wes!

I don't suppose at this point its possible to know whether or not they hybridize in the wild or not. We will have to wait for further studies to clarify this. I would be inclined, however, to believe that it would be hard for members of the vittatus complex and tanzaniae to hybridize though because they are not sympatric. The vittatus complex is mainly found in central and southern Africa in the Congo and Zambezi river basins, where as the tanzaniae exclusively in the Ruvu and Rufiji-Ruaha river basins in eastern Tanzania. I would consider the tanzaniae to be a separate population of the 'vittatus-like' clade that is located to the northeast of the rest of the population, as their genetics supports the idea that tatf is descended from a population of the vittatus complex that separated via allopatric speciation. I suppose that if they were to somehow come in contact with one another, they would be able to hybridize.

 

[Chicxulub]

Nicely done man, looks like a lot of time, a lot of reading, and a lot of passion to put something like this together.... i appreciate the info very much, and i thank you
i would very much like to go on a hunt to gather every ATF species and have a tank with all of them, its just that my Goliaths have so much size now that i'd need to grow out the new guys for so long so they could be kept together, not to mention putting 1 new ATF in my tank could be the match that ignites everyone into fighting, so i will stay with what i have. Maybe in a few years i'll try it
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Dunno how I missed this.

Thank you for your kind words. These fish are something I have become quite passionate about and I guess it shows. I've been working on this for a couple months now. When I eventually get to that point in my college career, I intend to do my dissertation on Hydrocynus.

I too want to collect all five species of ATF. I must say, I share your concerns about growing them out. My goliath is also growing at a very high rate, he's about eight inches now. My tanzaniae is only about 3.5 inches. I've lowered the temp in the main tank to 78-80 degrees and slowed down feeding as well. The little guy is growing but I suspect it'll be a while before he catches up. Do your guys take pellets yet? I observed a dramatic drop in aggression from my goliath when he stopped using fish as his primary food source. I certainly understand why you'd be concerned about adding fish to your delicately balanced system however.

I've said it before and I'll say it again, I think you have one of the nicest collection of predators out there.

 

[fugupuff]

I thank you for your time in doing some research on the distribution of these different species. From my experience, over the past 12 years, since they were made available again, I can chronologically list how the different shipments from different areas consistantly produced "different" batches, and I'll attempt to do that a little.

1999-2000
before 1999, there was an absent of tiger fish from the hobby for at least 5 years, almost none were exported. in 1999, while internet searches were at its infancy, I heard rumors of tiger fish in Michigan, it was 500 dollars, the this store called lurking in the weeds, near detroit. I flew out there to see it, but couldn't afford it at that time. I have pictures of that fish, it was taken on 1mp digital camera that I bought at the local target and then later returned. that is the fish that I called hydrocynus forskahlii, misnomer or not, it was a slender fish with a relatively small head and even shorter mouth. if you measure the entire lenght of head compared to the body, its the shortest among the groups, also like the one I have pictured above with the guy holding, the slender one

 

[fugupuff]

that fish was sold to some hobbyist in washinton state, and he kept it for over 2-3 years, and it barely grew, and remained slender, I actually should have a video of it feeding...