Raising Mixed Spawns

Having many fry and few tanks is a problem especially if the fry are not yet at the point where one can choose the best and cull the rest nor is it at the point where they can be sold or given away. Or maybe one just wants to make space for other fish and fry. One may resort to raising mixed spawns. It can be one of four cases:
Case 1. Same species, same strain just the different birth dates and/or parents
Case 2. Same species, different strains
Case 3. Different species
Case 4. Combinations of the other three cases.


Here are some tips and considerations:
Case 1. There is little to no chance of differentiating. Size is a clue but not always because there can be runts and shooters in the spawns thus obscuring any size differentiation. However, for genetics sake, keeping fry of the same parents together is recommended.


Case 2. A tip to avoid any mix up is to combine strains that are totally different and easily told apart. Betta spawns for example. Fry from an iridescent pair (royal blue, green, steel blue) will be totally different to fry of a red pair (aside from red, non-red siblings or non-red spawns altogether are alright). Metallic spawns (copper, dragon) can be raised together with non-metallic lines. Another obvious difference combination is raising long-finned types (HM) together with short-finned types (PK, HMPK); and raising fringe-finned types (CT, CTPK) with non-fringe-finned types (HM, PK, HMPK).
Live-bearers need more care because they are know to breed at a young age. Males and females should be separated to avoid any mixing of the lines. Then, same style of combinations as mentioned above: different colors, different fins.

Case 3. Telling species apart is easy but the question is what species to raise together. The first thing to check is size. The rule is the smallest fish is too big for the biggest mouth. Attitude and behavior is the next consideration. Keep aggressive with aggressive. Keep fast with fast. Keep tropical with tropical. Third is food. Basically, these species should eat similar or the same food because they are sharing the tank. But it can also be possible that different species ignore each other's food thus allowing more food variety. Several combinations that are safe and the author has tried himself: guppy-swordtail-molly and betta-scalare (angelfish).