The post-post-apocalyptic world has arrived in Fishtown, and there is crab cheesecake in it.

To wit: The Fin, a surf-and-turf-theme restaurant next to the Fillmore and Punch Line and beneath the new Brooklyn Bowl at Delaware and Frankford Avenues, across from Rivers Casino. It opens officially on Thursday, Dec. 9 with 220-plus seats, one of the city’s largest bars, a raw bar visible from the glassed-in kitchen, and an indoor TV screen large enough to be seen from apartments at Waterfront Square a block and a half away.

The Fin replaces Mad Rex, whose post-apocalyptic atmosphere rolled together all the cinematic bleakness of Terminator, 12 Monkeys, and The Walking Dead, including a helicopter suspended over the DJ booth, a smoke-belching airplane that appeared to have crashed through the dining room ceiling, and barbacks dressed in lab jackets serving drinks in IV bags outfitted with straws. Didn’t last long. Surprise.

The Fin is an ambitious project from the Crab Du Jour seafood-boil chain, and a pet project for Crab Du Jour’s director of operations, Jeffrey Schroth, who was given plenty of leeway from corporate. Schroth has passed along the same direction to chef Valentin Bay, formerly of Brauhaus Schmitz, and beverage manager Philip Search, formerly at Banh Mi & Bottles and Assembly.

Which explains Cajun crab cheesecake with berries on the dessert menu, along with more conventional options such as a root beer, Burning Apple cake cobbler, and a chocolate platter billed as schokoladen dreierlei as a nod to Bay’s Teutonic roots.

Crab cheesecake is not entirely uncommon, but it’s more often found on the savory side of menus. It’s just how it sounds: Crab is folded into a conventional cheesecake of mascarpone and cream cheese. Bay snickered at the initial reaction from those first hearing about it. “Sounds horrible,” he said, waving at the thought. Just taste it, though: Crabmeat’s salty tang plays off the cheesecake’s sweet richness, a synergy similar to that of salted caramel.

The menu runs the gamut from more casual dishes such as a few sandwiches, mac and cheese (with options such as pork belly an lobster), chicken and waffles, bison tartare, grilled oysters, and calamari, up to full-on platters such as U-10 scallops, swordfish, crab cakes, seared striped bass, jambalaya, grilled pork chop, and a $135 dry-aged rib-eye for two. Most entrees come with sides.

There’s also a surf and turf charcuterie ($19) composed ofsmoked and cured seafood and meats, seasonal pickles, and baguette. (Over the weekend, the platter included gravlax, smoked trout, smoked whitefish, sopressata dolce, seared foie gras with blueberries, white anchovies, and a house salad.)

Search said he was building an extensive beverage program with 16 wines by the glass, and 125 bottles to start, with an eye toward 320 bottles; 12 beers are on tap; and a cocktail list starting at 20 drinks made from house-made infusions and syrups.

Initial hours: 5 p.m. to 2 a.m. Monday to Friday, noon to 2 a.m. Saturday, and noon to 10 p.m. Sunday.