On singleplayer, you can easily tame a giga with cooked fish meat by:

1. Making sure your giga is knocked out

2. Wait until its torpor is low but not on the cusp of the giga waking up

3. Spam all required narcotics to make its torpor high again (or every one if the amount of required narcotics equates to not even all of its torpor)

4. Place down a bunk bed, sleep, die after you wake up, respawn fast enough to get back your bunk bed

5. Repeat step 4 until your giga is tamed or step 3 if you need to use more of your narcs

6. Enjoy +16 levels if you did it with a lvl 150 giga