Ideas for a pescetarian Turducken (aka a fish in a fish in a fish) I've made a Turducken every year for the past several years as part of an end-of-year gathering with friends. This year, we have a pescetarian (no meat but fish is fine) coming as well, and I'd like to do something analogous for him. I'm wondering if anyone has any experience with the challenges of putting a fish in a fish in a fish.

Some of the limited suggestions I've found online propose an innermost layer of some kind of "fish mousse" or crab meat or equivalent. Not bad suggestions, but there's a certain aesthetic appeal to the profile cut and appreciating the layers of meat fish that I'd like to maintain if possible.

Does anyone have any experience with this or ideas?

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UPDATE: I stopped by the local fish market today to talk things through with the folks there. They are willing to debone the fish for me*. I am enamored with the idea of a strictly fish-in-fish-in-fish setup (e.g. no cheating with crustacean meat), but not tied too firmly to it. Their initial suggestion was an outer layer of salmon, a middle fish of something light and white (e.g. whitefish, haddock, maybe cod), and for the innermost: butterfish. The market owner wasn't there today (Sunday), but I'm going to talk this through with him tomorrow as well.

Re cooking: I unfortunately have neither experience nor the requisite equipment for sous-vide. I concur that layering largely independently-cooked fillets may be the best means of preparing this dish. If outermost fish still has head, skin, and scales I imagine the whole dish can be assembled in a manner that hides the actual preparation (and probably spends a little time under heat as a whole assembly, to allow flavors to blend). The market owner is a chef as well, so I'm hoping that talking this through with him tomorrow will be helpful.

*General Advice for others interested: After 6 years of making turduckens, I am quite capable of deboning the birds myself but have found that having a professional do it for me is $20 very well spent.
Unquestionably, I'd consider the colors of the fish. It seems a natural that your outer fish should be salmon (head, tail and skin intact, scaled, gutted, with spine and rib bones removed). I'd try to present the whole thing as if it were a whole salmon. Cut through the center of the salmon for presentation, that could be a tremendous presentation. (You've got me interested, I want to try this myself! :) For the inner fish varieties, consider very clean fillets of fish of different levels of oiliness and color of cooked flesh. Maybe halibut for the middle of the 3 layers and tuna for the center? It would be a neat trick if you could somehow fully cook the outer layers but keep the inner tuna layer rare. I'd stuff the very center of the whole thing with some kind of shrimp or crab mousse. I'd spread a deeply flavored and colored compound butter on the outer surfaces of the other fish. What fun! Good luck.

EDIT: SAJ14SAJ mentions sous-vide as a good cooking method. I concur. If you do that or very carefully poach the outer two fishes in advance, then sear the tuna and assemble everything, it could be epic. The tricky thing is deboning the outer fish. Here's a video showing the technique Deboning a Whole Trout. You might even consider presenting the whole thing chilled. Chilled, I'd forgo the butter and use brightly colored mousses between the layers of fish instead.