Cousin Itt wrote: ↑Sat Oct 31, 2020 11:33 pm
I have a brown trout in the freezer, it's about twice the length of your mystery piscine but you're welcome to the otolith (if you can tell me where to find it).
I've found a couple of videos showing the two main techniques for taking otoliths. The first is the
'top down' method. This is the method I was taught, though I don't normally remove the face like the guy did in the video. I normally go at a shallower angle, to try and expose the brain and then you can pull out the brain and then normally see the otoliths sitting in their little cavities. (If you're doing it with a really fresh fish, when you remove the brain sometimes you can activate the nerves and get the fish to twitch which is kinda creepy but fun). I like this method on fish I've not worked with before because you can go in gradually, shaving off layers of head until you reach the brain/otic capsule without having to know exactly where it is in advance.
The second one is the '
bottom up' method. It's a technique I only learned a few years ago and is really good though I'm less comfortable with it. I suspect part of that is lack of familiarity (I've only done it on a couple of hundred fish, compared to a few thousand for the first) but It also feels like a technique where, if you're unfamiliar with the fish or there's some damage to that area, it's really easy to get lost in bone fragments and not be able to find the otoliths (especially if they're small).
If your trout is a decent size, which sounds like it is, they should be fairly large (I'm going to guess just under a centimetre in length). They are white like the bone but they are a different texture - much harder. You can hear when you've got them with your forceps, even if you can't see them, and they are much more inflexible than the surrounding bone. If you go with the top-down method then they can be difficult to remove from the capsule but if you've found them and can't get them out then you can use either your knife to cut or the forceps to break the capsule open. If you go with the knife do fine slivers - it should open up quite quickly and if you cut too deep you'll cut the otolith in half.
If those videos aren't clear enough I can try and make my own. I did go to Tesco today to see if I could get some heads but the fish counter is closed until wednesday so I won't be able to do anything until then.