Subject: Can a hydra smell other hydras or fishes?

To Ingrid Dodge, Grad student, Immunology (she answered my last question, so I hope, 
she can answer this question too)
You said, hydras have mucus. 'Cause the clown fish has this mucus too does the hydra 
don't kill it if it touche its tentacles. does this mucus lame the Cnydocil (I don't know 
how to write it) or is the fish immun against the poison?
My teacher supposed, the hydra can smell and so the hydra "says" to the tentacles: 
Don't touche them?
Well, I ask you: What's the truth?
Thanks, joelle

P. S. Do you want to know what's a sixth-form-college? It's a college in Switzerland. It 
has the level of an university, but it's  for younger people (I'm sixteen)

Re: Can a hydra smell other hydras or fishes?