One must be careful with common names, since they are not always commonly used. I suspect by "lambchop" you are referring to Trigonostigma espei, but in local stores I have frequently seen this name applied to a close relative, T. hengeli. I'll give you some data on these fish, and photos.
As a result of their study of some of the cyprinid fishes, Kottelat & Witte (1999) erected the new genus Trigonostigma for this and the three closely-related species [a fifth species is now described, more below]. This name is from the Greek trigonon (=a triangle or hatchet) and stigma (=a spot or brand). T. heteromorpha is the type species for the genus. This separation was made on the basis not only of the striking similarity in colour and pattern, but more on the spawning method that differs from all other rasbora; in these species, the female attaches the eggs to leaves, usually on the underside, and the male comes along to fertilize them. Other species of rasbora are egg scatterers. Subsequent studies (Liao et.al. 2010, and others) have confirmed this division on the basis of phylogenetics. No one has disputed that this genus is monophyletic, i.e., the species are all descended from a common ancestor.
T. heteromorpha is the largest species of the five, usually just under two inches/five cm, and well known in the hobby as the Harlequin Rasbora. T. espei and T. hengeli are very similar, but the shining copper spot on the latter is indeed stunning in a dimly lit aquarium. Both attain 1.6 inches/4 cm. A fourth species in the genus, T. somphongsi, has a dark broad stripe [rather than a triangular mark] that runs laterally below an iridescent stripe; this species occurs in the basin and floodplain of the Menam River in Thailand and is very rare. A fifth species, T. truncata, was described by H.H. Tan in 2020 and in appearance is more like T. heteromorpha than the other species in the genus. Photos of the five below.
All these fish must have a good cover of floating plants to subdue the light and make them shine. They will tend to remain mid-level, and in a group. A group of more than 10 is advisable, closer to 12-15, especially important for T. espei and T. hengeli. Very peaceful, not known to fin nip and thus work well with sedate fish like many of the gourami.
Really interesting, you are so knowledgeable! You are correct, I did mean
Trigonostigma espei.
I was just checking out my tank to see how the floating plants were doing and a couple of them had gone brown and mushy over night. Removed those, and since I've temporarily moved all of the frogbit (Limnobium laevigatum) into a little plastic 2.5 litre tank. (Not heated or filtered). I have been trying to figure out what the problem was and from what I've read online it seems like surface movement or temperature could be the problem. Previously I did remove a few of the loose leaves that had turned yellow/brown but they had transitioned from yellow to brown whereas the ones that had died over night were green yesterday and mushy brown today. Not sure what went wrong, so I thought moving them into the plastic tank would remove two of the potential causes (heat/movement) and I could see if they would perk up again.
In videos of people's tanks with floating plants like frogbit or duckweed, it seemed like their tanks had none or very little surface movement. I don't
think my tank is high flow, but there aren't any spots on the surface that are completely still either. So I'm thinking maybe the amount of surface movement might mean that my tank isn't really suited for floating plants like the frogbit. I trimmed the tops of some of the hornwort (ceratophyllum demersum), and those seem to be doing the best out of all my plants. The trimmings could grow out at the water's surface and act like floating plants but I don't know if that would be good enough for the rasboras mentioned in your reply. They could also just clump into a corner and be of no use to fish who need surface cover.
Maybe I should look into fish that don't need surface cover and like a fair bit of surface movement? I'm not sure.
The issues with the floating plants could be something else entirely. Maybe the levels of ammonia, nitrites and nitrates leeching from the aqua soil. I could also consider removing some or all of the air stones, maybe switch to a sponge filter. But I've heard that flow and oxygenation are important also.
The reason I was looking at the
Trigonostigma espei is because I would really enjoy a school of small/nano/micro fish with tight schooling behaviour. From what I've read and seen on Youtube so far, rummy nose tetras and harlequin/lambchop rasboras seem to have the best schooling behaviour.
My ideal school of fish would be 2 cm or under (the individual fish, and the smaller the better) and would swim around together in a school. I don't want a shoal of fish that would just inhabit the same tank/general area. Before I was considering ember tetras but from what you've said before, they can be quite shy and need good surface coverage from floating plants. This is probably wishful thinking, and I doubt there are any fish of that size and behaviour that my tank could suit. I do like the colouring and size of the chilli rasbora, but I can't quite tell if these fish properly school or whether they shoal.
My reason for wanting a school of fish that are small in size is so that I can keep a bigger school together, (and still have enough room for a centrepiece fish or maybe a cleaner like the whiptail catfish you suggested) and for there be enough space for them to live comfortably without being crammed.
Do you or anybody have any suggestions or advice?