I don't now but I believe that you can catch as many as you want when you encounter them.
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There are many Pokemon you catch that are similar in sapphire and emerald but there are many Pokemon emerald can only get and not sapphire.
All if you have a gameshark
There are 386 Pokemon in the game. Some Pokemon aren't available to capture in the game, including some that have to be traded from other games, and event legendary Pokemon.
about 150 Pokemon . Unless you want to count legendary about 160.???????????????? I don't know the exact amount!!!!!!!!!!
four without cheats Articuno Zapdos Moltres Mewtwo plus one of the legendary dogs; entei, suicune or raikou