I believe they can communicate but are probably unaware that they are doing so. A few examples,from observation, nothing scientific implied or claimed. Cast a buzz bomb in front of a school of pinks, almost immediately several will dash towards it, if the first one misses another grabs it. It's hooked and within a few seconds all the others have disappeared--cleared out. Is the hooked fish indicating it is in distress, I think so, the other fish sense the danger and disperse quickly from the area. I have seen this reaction many times and not just in salmon. It could be instinctive, I don't know. I have been fishing chum when some resident orcas came through. Emptied out the bay. Did they each sense the arrival or did they did they pass the message on. I have also had triple headers when chum fishing, all on within 10 seconds, boats around me experiencing hookups at the same time. Not much communication there. I think in the fish world its not a matter of "talking" but rather communication based on instinctive reactions.