I have quite fine gravel anyway because I was planning on getting some sort of bottom feeder and I'd read that sharp gravel could hurt their barbels. It's sort of like black quartz but it wasn't labelled as such. I was thinking about maybe, instead of getting 8 or so harlequin rasbora, getting six of those and six cherry barbs because I like cherry barbs and I've read that they can help make loaches feel safer. By the way, should I get one of those little tanks that fry can swim into for safety? I'm not too bothered if any of the species breed but I'm wondering whether I should just let the fry take their chances in the tank or actually grow them and sell them for store credit.
I know you are not intending loaches now (from your subsequent post) but will just explain what you mention about cherry barb making loaches feel safer. This refers to what is termed "dither fish" mainly with cichlids but it applies to most fish. "Shy" fish will tend to be much less so if they have other upper fish present. If there are shoaling fish above them, the loaches seem to assume it is safe to be out and about. This has it limits, but it is generally the case. It really doesn't matter if it is cherry barbs or rasbora or any other peaceful fish.
I would not mess around with fry compartments. First, this takes up valuable space in a smallish tank, and second you are not likely to see fry anyway. Livebearer fry tend to survive in most cases, some of them anyway, because they are born larger and can feed off normal foods from the start. With egg laying fish, in most cases the fish in the tank will eat the eggs the moment they are laid. Sometimes a couple may survive; it can depend upon how the species lays its eggs, as well as what other fish are present. Fish like the characins (tetra, pencilfish, hatchetfish) and cyprinids (rasbora, danio, barb, loaches) are egg scatterers (there are a few exceptions) which means the pair dive into a thicket of plants and a cloud of eggs is released and fertilized immediately. The eggs are usually a bit sticky and adhere to the plants. In nature the parents would swim away to continue spawning or whatever, but in the aquarium they are in close confinement and frequently begin eating the eggs once they have finished spawning. Also, other fish in the aquarium pick up the chemical signals (pheromones and allomones released by all fish) and know what is going on, and will frequently hover close by and gobble up the eggs within seconds of there being expelled.
I occasionally see a fry that has managed to survive because of the very thick plants, but it is not often unless the fish is the only species in the tank and if they are not inclined to eat the eggs/fry themselves. I have tiny pygmy cory fry in with the parents in my 10g as we speak. But even if the eggs survive and hatch, next issue is food. The fry of egg layers are very tiny compared with livebearer fry, and unless you specifically provide microscopic food they are left to forage the live foods in the aquarium, of which there will be some in most tanks that are planted. I added some dried oak leaves in my 10g to provide infusoria which is an excellent first food for fry, and obviously some managed on it. I also have
Farlowella vittata fry growing up in this tank which is why the leaves are there to begin with, and these fish being algae eating will not bother fry, so there are no predators in this tank. Unless you set up a dedicated spawning tank, and remove the parents post-spawning, and then saturate the tank with microscopic foods, you are not going to have many fry survive to be sold.
Byron.
