Most egg-scatterers prefer to breed on soft locations. The one ideal plant for this is java moss. Other plants like anacharis, cabomba, hornwort, and the roots of floating and terrestrial plants work for other fish like goldfish. Hair algae is also an excellent spawning medium for small egg- scatterers.

There are a number of spawning mops sold commercially. I have bought a stiff plastic-like one for aquarium fish. They never used it. I also bought a huge black hairy one for the pond goldfish. They never used that either. Fish prefer live plants or even the base around pots and fake plants much more than artificial spawning mops in my experience.

You can make your own artificial spawning mop. Get some natural yarn (no dye). (If you can only find colored yarn, boil it first in water at the pH of your aquarium to leach out any color before adding it. Colors will bleed at in differing amounts depending on pH.) Use as much as is appropriate for the size of the fish in question. For small aquarium fish like danios, barbs, tetras, white cloud mountain minnows, etc., you might take about 1/5 of a skein but for large fish like koi and goldfish in a pond, you would use the whole thing. Wrap the center of the yarn with natural twine, another piece of yarn, or fishing line. Then, cut the ends off (all the loops at either end). This gives something akin to a 1000-legged octopus or maybe only 6 legs for small fish. Tie this where it is wanted in the aquarium or pond.

Remember that these natural spawning sites and artificial mops only work if the fish in question is either an egg-scatterer or an egg depositor that likes the item in question. For example, cories are egg depositors but they will stick eggs in java moss and the other mentioned plants and yarn mop readily. A fish like the rosy red minnow which is an egg depositor that only uses hard surfaces is not going to use these sites. Live-beared and mouthbrooded fry will often hide out in the mentioned live plants and yarn as will insect larvae if there are any around. If the plant or mop is floating, labryinth fish may incorporate it into the nest.