An odd couple, octopus and grouper.

[AleG]

A couple years ago when I was snorkeling in the island of Koh Kood I noticed a curious thing, I found an octopus and a longfin grouper sticking together at all times. Has anyone seen behaviour like this?

I filmed them around the reef and no matter what the grouper would always stay close to the octopus, it was the first time I've seen something like this and I don't know if it's a known behaviour or those two had a weird thing going on.
At the end of the video there's an extra bit, where the octopus ... well, no need to spoil it.

 

[aviator8]

well that is interesting. Not sure whats up with the behavior but they sure seem to be comfortable with each other and acting as a team.

 

[Vicko]

There are a couple of species that got used to feeding on stuff that runs away from a octopus.
One of the common ways of spearfishing for octopus in the Mediterranean is to find the fishes following them.

 

[RyanT]

Wow, thanks for posting, this was amazing. I can't say for sure, but it looks like the fish and octopus may have had some kind of cooperative hunting thing going on. In the Caribbean, trumpetfish will often hide behind larger fish and use them as a blind to sneak up on their prey items. It looks like something similar may have been happening here. Interestingly, you don't normally see octopus out on the reef during the day, so it makes me suspect that two were actually hunting cooperatively instead of only the grouper benefiting.

For reference, check these out.

An inter-specific behavioural association between a highfin grouper (Epinephelus maculatus) and a reef octopus (Octopus cyanea) | Marine Biodiversity Records | Cambridge Core

Interspecific Communicative and Coordinated Hunting between Groupers and Giant Moray Eels in the Red Sea

 

[Altamira]

I think it was in Blue Planet II, where they showed a segment where an octopus, and a Grouper (if I remember correctly) were a hunting pair. The Grouper would point to an area where some fish were hiding in the coral, the octopus came over to hunt, using its tentacles to grab some fish while scaring out others into the path of the Grouper. It was fascinating.