"My cat is not liked by Tono because he does not like animals."
Translation:Kucing saya tidak disukai Tono karena dia tidak suka hewan.
'oleh' can be omitted if the passive 'di-' verb is followed directly by the agent/actor.
'oleh' must be used if the passive verb is followed by something else than the agent/actor.
agent/actor = the one performing the action of the verb.
Here is another sentence where it's easier to put 'something else' after the "di-" verb :