I would not use tissue if by this you mean, "tissue" such as Kleenex or Facelle Royale or whatever. These are paper and will fall apart and make a mess. They can also have dyes and chemicals. I don't know if fish might mistakenly eat the bits, but I would not risk it. You can buy spawning nets made of fine mesh nylon; I've used one of these when I found and saved a couple eggs. Put a dried leaf (oak, maple, almond...just make sure it is dead dry) or two in the bottom of the net and infusoria will be present from the decomposition.
There is much more to this than simply feeding the parent fish well. I would not recommend over-feeding fish for any reason, and that is only making the environment they live in worse biologically.
The difference between fish spawning in their natural habitats and spawning in the aquarium should be obvious--the space. I am sure some of the eggs are eaten in the habitat when fish spawn, but the area they spawn in in so vast that many eggs will escape predation. In our aquarium we are confining fish to a very small area by comparison, and the parents as well as any other fish present (if you have them in a community tank) will be much more likely to know what is going on and eat any eggs they come across. Fish release pheromones when they communicate spawning, and others in that species "read" these signals and know exactly what is occurring. It's like sounding a dinner gong.
