Don't Buy These

Publix had northern Canadian Lobster tails on sale, down here in Daytona. Raw. Previously Frozen.
Sorry I didn't take pictures before cooking.
They were split down the backbone.  I boiled them for 2 minutes.  They came out like mush.  And VERY SALTY.  I should have cooked them on the grill.
 
The results:

I don't know about lobster, but with shrimp mushiness can come from improper handling at the time of harvest (too long a wait before processing/freezing) or having been frozen too long.

I bought some black cod a while ago that looked awesome in the store.  Threw it on the grill and it just turned to mushy goo.  Talked to my fishmonger and he said that whole slab of cod did the same thing to all his customers and he suspected it wasn't processed fast enough.  He comped me with a couple free fresh salmon steaks.

Perhaps they were already cooked?

no Don they weren't cooked. they were raw.

OK.
 
I used to buy frozen snow crab claws, when my wife got live blue crabs, and I was disappointed in them.  Then I found out that they were already cooked!  (D'oh!)

these were frozen & then thawed before we bought them.
if they were still frozen when we cooked them, it probably would have been better