Loaches Online Forum

In an effort to answer Azmeaiel's question about sexing Gastromyzon ctenocephalus, I decided to take some pictures to try and illustrate the differences between the sexes.

The fish were not exactly cooperative, but I managed to get these two overheads and composite them together so you can compare.



The fat bodied fish on the left is a female and the slimmer right hand one is the male. This is the first time I've done a side by side comparison. It's obvious from the specimens we've all seen that there appear to be two sub-species of this fish. Like Gold Nugget Plecostomus, there are small spot and large spot individuals, plus they have different fin colouring and markings.



So we bounced around ideas about regionally seperated species populations, etc. I've always kind of settled on that idea and not actively compared my fish. There's 5 or 6 mixed ones, so not a huge sample to compare. I looked at the overhead shot above. Although these fish both have large spots, the fins are of the two different types. I looked closer....the nose shape is different, plus the pectoral and pelvic fins are different shapes. The pelvics particularly are much larger in proportion to the pectorals in the right-hand fish.

So, in trying to illustrate sexual differences, I think I may have discovered that these might actually be different species. They both share the red nasal nares that we've always associated as a G. punctulatus trait. Recently, of course we've accepted that this fish is actually G. ctenocephalus.....but which one? Or are these two just sub-species where population isolation has led to different traits other than fin markings?

The thick plottens......

Martin.

Very interesting!
Well, here we go again!

cool stuff.
o boy o boy o boy!

Mike

the plot might thicken even farther

the individuals I bought over here in aus are identicle to both fish you have, I have large skinny individuals with bigger fins (I also took these to be males) and smaller more spotty fish with fatter bodies (possibly females) Strangley though I notice the big fish goes through a lot of colour changing, from light to dark. The tail markings, positioning of spots seemes to be roughly th same so I assumed they were the same fish. will try and get some photo's also.

Nice!!

I have 12 G. ctenocephalus, all of them have no color (transparent) at its dorsal fin's membran, big possibly its geographical/locality variations.

when I tried to take phootos I moved the fish to a small container, then put the continer in some direct sunlight for a few minutes while trying to take shots. One of the fish had a bright green irridescence while the others had a very weak coppery sheen. Unfortunatley it didnt appear at all on the photos.

Martin and company on a Saturday mornin',

Speciation, evoloution and biogeography right there in your fish-tank !

These are fast water spp likely from hilly/mountainous areas, yes?
You can get situations where each stream is essentially isolated from the next, so each will act as an island and you'll get genetic drift within the population, possibly in this case in the form of changing patterns and fin sizes.... or the conditions of the stream may be different enough to force adaptaion. Over time you get a new and distinct species.

Here (Jamaica) we've got these hummock limestone hills called Cockpits. Each Cockpit can act like an island and can have several distinct endemic snails on it. We've also got a similar thing with hillstream gobies. Slightly different in colour and fins in different watersheds around the island.

I suppose i'm just repeating what you'd already said, but i love the process so thought i'd put in my two cents.

It would be interesting if the industry could reference or name the fish by river/stream/drainage/watershed or province or GPS the collection sites. For those of you in the industry that may be a way to market to the serious collector.(?)

Andyroo

andyroo wrote:It would be interesting if the industry could reference or name the fish by river/stream/drainage/watershed or province or GPS the collection sites. For those of you in the industry that may be a way to market to the serious collector.(?)

THIS is a good idea for this type of fish. And 2 cents are worth more here than in some places

Isn't it pretty common for male and female fishes to have different coloration, different size and shaped fins? Sometimes males can have even different head and body shape.

Often fishes, even those from same section of streams, have varying color pattern. One easy case is that of Pangio myersi from eastern Thailand that comes in varying color and pattern: big bands, small bands, blotched [both yellow and tan of varying size], dark overall, yellow over most of the body, and albino.