If your fish are sexually mature, as they will need to be to identify the sexes - and may not be if you have just acquired them - in addition to the methods suggested, you can also easily identify the sexes by their body shape, especially easily when viewed from above. This is also reasonably easily visible from the side (as can also be seen from the photographs in the previous post), but if you can't see the difference from the side, try from the top if you need. If necessary, if you can't see easily when they are awake, do it when they are asleep, using a torch (flashlight). Males are narrower in the body, females wider, especially, but not only, when they are in spawning condition.
If you do decide to try to spawn them, you might like to consider my method. They are really not a difficult fish to breed, provided that, as with all fish, they are in good spawning condition - females good and plump, males robust and well-colored. I generally use a 60 x 30 x 30 cm (24 x 12 x 12 inch) tank divided into two sections, but you certainly don't need to divide your tank - that just gives an idea of the volume of water they will be prepared to spawn in. You can use a 24 /12 /12 tank as is, or similar. They are very accepting of (and their eggs will hatch in) a broad range of water hardness, though their preference would be on the softer side. pH around 6.5 to 7.5 will be fine, though they will spawn out of these limits. (Best to age the water a few days if you are using tap water. If the water is very hard you could use half rainwater, or whatever is needed to soften it. (Soap lathers easily in soft water, as a guide.) They would spawn in pure rainwater, but you'd be better off adding add some mineral-rich water before rearing the young - just easier. I normally fill the tank to about 3/4 full. I prefer somewhat subdued light for all egg-scatterers, which is what they are, but this is by no means critical. Aeration very gentle. 24 to 27 degrees C (75 to 81 F) will be fine, or roughly the same as the tank they're in, within this range.
I use a single large green acrylic wool mop with each pair/group, or well-washed coconut fibre as the spawning medium, for them to lay their eggs on. (Best to boil new coconut fibre first to remove tannins.) You can use fine-leaved live plants as well, but this is often less convenient! Leave some swimming space around the medium. I tease it open to allow them to move through it when spawning. If you introduce a pair at around midday they will usually spawn the following morning. (I don't introduce them too early in the day prior to their spawning as males will sometimes damage females which are unwilling to spawn at this time. Males are not so fussy about times of day!) You should not need to separate the sexes prior to spawning unless they consistently spawn in your community tank - which I presume is where they live. This is unlikely, but I guess not impossible. If the female/s is/are plump, they'll be fine. The move to fresh water is normally sufficient to induce spawning. If you can set-up more than one pair, this will improve your chances of success! I usually set up one male to two females in each tank but in your situation I would use one to one, unless you have more males than females. (I use trios to get more eggs per tank as both females often spawn and fertility is fine with one male. If you have more females than males you could do this too.)
If the breeders are in good spawning condition and happy with the environment, they should spawn on the morning following introduction, occasionally on the following day, very rarely later than this. Watch the female for damage by the male if there is no spawning, though this is not a big problem with them - but it happens. Eggs will be spread through the medium, many also on the bottom as they are only slightly adhesive - easy to see with a torch (flashlight). Best to remove breeders when spawning activity ceases (chasing, with male following the female through the spawning medium). Be careful not to catch out eggs with a fine net by mistake - happens easily, use a coarse mesh size if you can, otherwise just be careful. You can lift the spawning medium out of the water while you catch the breeders - much easier (!) and this will not bother the eggs provided you are reasonably quick. The spawning medium can be returned and left with the eggs, and removed once they hatch by shaking it quite vigorously under water then lifting it out - the fry will not be bothered by the shaking! Tiger barbs are not bad spawn robbers, but will eat some eggs - common problem with egg-scatterers. (A protective screen can be used, but you don't need to bother with this.) Pairs are not always spawning-compatible, and spawns can range fro 50 to a few hundred from a large female, but lots of things influence this. Fertility can also vary substantially.
Eggs will hatch the following day some time, depending on temperature. Larvae will hang on the sides or lie on the bottom for around 4 days (again temperature-dependent) until becoming free-swimming and ready for a feed. This is not as easy to recognize in tiger barbs as in most other species, but look very carefully for slightly jerky forward movements of the larvae. (You'll have to look closely!) Some will move up the glass, especially in corners or darker areas.
They easily swallow newly hatched brine shrimp as a first food, though you could use (good) infusoria for the first few days. You will have far less or no success with dry diets, even very fine ones, though a few may come through, so it would be better than not trying at all! Good luck with them!
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