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I got a batch of Flash plecos in last year and thought I might try to sex them now. Most are around 2-2.5 inches SL. I have a couple obvious males, one 4+ incher that I didn't bother taking pictures of. The others are up in the air. Pretty sure I have mostly male but would love to find a female in the group somewhere. Some of the pics got cut off, I expected them to be thumbnails that you could click on to see a bigger pic.

To see the full size pics, can go HERE. Fish 1 and 2 inside are in an inside display tank. Fish 1 2 and 3 outside are in the fishroom and labeled fish 3, 4 and 5 below.

Fish 1:









Fish 2, only took 1 pic as it looks male to me:



Fish 3:









Fish 4:









Fish 5:

i'd say 1st male, and 2nd female

Lygen wrote:i'd say 1st male, and 2nd female

The 2nd is definitely a male. Females never get that hairy. Not sure about the rest.

panaque wrote:

Lygen wrote:i'd say 1st male, and 2nd female

The 2nd is definitely a male. Females never get that hairy. Not sure about the rest.

my bad.. in the hurry i thought there was only 2 fishes.. so that would be: 1st male 2nd male 3rd female 4th male 5th female for me

L204 are hard to sex when not fully grown. These all look to young.
But I can spot a lot of odonthodes on most of them so that would make them males.

When I tried to breed L204 I began with 12 specimens. Half were raised from young juveniles about 3 inches TL and half came in as adults. I began trying to select and remove what I considered to be excess males for a breeding group.
I used visual examination to see which were males with heavy odontode development.
I also use the touch test with an assumption that if all things were equal, non-obvious males would feel spiny compared to the females. I final had reduced the group to 6 but then some I had considered to be females turned out to be males. I finally ended up with what I thought were 1 male and 3 females or perhaps a couple pairs.
I also tried to use head shape differences but in the end, none of my choices seemed accurate or I may have had many more males than females from the beginning.
To me, this is a difficult species to sex at any size.
And an even more difficult species to breed. I tried for 4 years before I finally gave up and sold and gave them all away. All I can do is wish you much better luck than I had. I had some of mine for at least 6 years. I gave 2 local friends a couple each of my adults and each lost them within a month! I found them to be very hardy so I was very surprised the friends had lost them. They are not bad algae eaters in large enough tanks but I suspect my friends did not realize how much food they needed. Algae alone is not enough. Nor is wood. They need a lot of food, wood and warm, clean water. I fed mine about 50/50 earth worm sticks and Spirulina sticks. These were also supplemented with frozen blood worms and sometimes live Black worms.

Ive just got 3 hope there not immpossible to breed

Far from impossible but far from easy either.

I've got a total of 6 and I've had them all well over a year. I find them very slow growers, hardly having grown much in this year I've had them. Perhaps it's what Apistomaster posted, maybe I'm not feeding enough. I can say they will shed the wood quicker than any other genus I've kept. I have 4 in a 20L and 2 more in a 26 hex, and they are chainsaws. Gravel vaccuming while doing water changes is a must, filters get clogged easily they have so much wood debris in them.

I do however find them very hardy. I did a test to see if they'd grow better over the summer in a pond. I put 2 flash and 4 L205 in a 100g rubber maid tub outside for the summer last year, they were out there 6+ months (in KC, MO). I lost 2 of the L205 but the flash were fine. Comparing them to the others in the fishroom, I do see better growth on them, so maybe it did help.

So best case, which is what I feared, is I have one female in the group. I'd love to get my hands on some full adult females. If anyone knows of where I could get some, I'd pay top dollar for them plus shipping =) 2 would be fantastic...tough find tho! A guy can hope...

What do you mean with 20L. Would that be 20 liters?? If so (but I can't believe) that is way to small tank for these fish. They need big tanks and as much water as possible. They really need clean water. I have bought about 20 specimens over the past years. All but 1 were males. Now I have selected my breeding pair and have been together for 1,5 years now. They have been in a cave together but not yet spawned.
Lot's of space, lot's of wood, not a lot of meaty foods, lot's of fresh clean water and water flow is what these fish need. Good luck.

Here is a picture of my breeding pair. Fish are over 15cm TL. Just to let you see how a male and female look like.

jac wrote:L204 are hard to sex when not fully grown. These all look to young.
But I can spot a lot of odonthodes on most of them so that would make them males.

Exactly what I was thinking Jac.

I have bought about 20 specimens over the past years. All but 1 were males.

I have 3 to pick up on wed quite large hope there not all males as there so hard to source in the north east of england i was lucky that a LFS had good contacts to get me large ones ordered 6 got 3 delivered.

if i get all males would love to find females in the uk ..

It isn't rare to receive more males than females when you buy adults.
It may have something to do with the males are being removed from their chosen spawning caves where they are already cornered and the females my be more prone to roaming.
Just a hypothesis.

Odontode growth depends on status and when in the breeding cycle your fish are in. Dominant males can be very spiky and non-dominant males may be little different from the females.

jac wrote:What do you mean with 20L. Would that be 20 liters??

Sorry, not used to international forums. 20L = 20 Long, which would be 75 liters.

DaveW wrote:

jac wrote:What do you mean with 20L. Would that be 20 liters??

Sorry, not used to international forums. 20L = 20 Long, which would be 75 liters.

75 liters does not say very much either: the tank can be 50, 60 or 70 cm long

This wil have a huge influence on what can be kept. In europe the standard tank is shaped different from what you are used to - and therefor it would be best to mention the sizes

USA standard 20 US gal long is 70 liters and it's dimensions are 30 X 30 X 75 cm long. It has an excellent surface area to volume ratio for this small size of tank. It is my standard "small" aquarium.
My other standard size, "large" aquarium is the 40 US gal breeder tank.
About 151 liters. Dimension in inches: 36 inches long X 18 inches wide X 16 inches tall. In cm: 91.4 cm X 45.7 X 40.6 cm. This style has a very favorable surface area to volume ratio. Probably more similar to the European standard tanks?

In the USA, one of the most popular sizes of tanks sold is the 55 US gal show tank.
It is 48 inches long X ~13 inches wide X 20 inches high. It is about 208 liters.
121 cm long X 33 cm X 50.8 cm high. These have a very poor volume to surface area ratio.