Best way I've found to tame is wait until sleeping, equip ghillie, walk up behind it crouched and use the harpoon launcher to net it... It will say "cannot feed - is not sleeping" but while still netted it will stand and curl up again... I can usually get two feeds in the initial net before it wears off, if you're on a boosted server that would be enough to tame one fully if you have really big fish size 2.0 or larger