For a chef who began as a guppy here five years ago with only 23 seats at Little Fish, Mike Stollenwerk's seafood ambitions have expanded lately at the empire-building pace of a busy hatchery.

There has been the move for his original BYO, the welcome evolution of his flagship fine-diner (Fish), and, most recently, a foray into the ever-competitive world of Philly bar food with Fathom in Fishtown. It has provided, among other things, opportunity for an ocean's worth of more seafood metaphors, which, as you can see, most writers covering Stollenwerk find irresistible to the point of being blinded.

A clever place from a rising star who's "putting the 'fish' back into Fishtown"? That couldn't be bad, now . . . could it? I asked myself that question repeatedly as I dipped my fork into a bowl of Fathom fries that were at once decadent and inedible, the fresh-cut spuds topped with crab, oozing mozzarella curds, and a drenching of crustacean gravy so achingly salty, it was like drinking liquefied Old Bay. But I'm getting ahead of myself.

First, with so many changes swimming in the tank for this sudden seafood mogul, it was time to return for a status check on all his projects before his roster grows yet again - with a (still unnamed) BYOB in Brewerytown this fall, followed by yet another potential move - this one for Fish, to splashier Center City digs.

That's still tentative, and it seems too early to think about moving this year-and-a-half-old pearl - especially since it has finally found its luster.

Fish resides at the top of the Stollenwerk food chain, a trio of sleek burgundy rooms near Rittenhouse Square where his most upscale ambitions are expressed. There have been some nice dining-room refinements since my initial (high two-bell) review last year, and the wine list has continued to evolve into intriguing directions. (Try the knockout vintage rosato from R. Lopez de Heredia.)

Most important, though, the kitchen, led by chef de cuisine Justin Petruce, has begun to show some real inspiration, with creative plates that bask in true seasonality, cutting-edge techniques, and vivid flavors. Scallops come alongside new spring potatoes tossed with house-cured bacon in a bright-green vinaigrette of chef-foraged ramps. Quick-smoked fluke ceviche arrived beside almond milk foam, tart Meyer lemon gelée, and sparks of pickled rhubarb. Beautifully crisped halibut posed atop black trumpet mushrooms whose inky juice swirled into velvety creamed spinach.

This was exactly the kind of progress I'd hoped for, earning Fish kudos as the city's top seafood kitchen and, now, the well-deserved bling of a third bell.

The new incarnation of Little Fish, meanwhile, which moved a few blocks north to the former Salt & Pepper space at Sixth and Fitzwater Streets, hasn't made quite such advances. It's still an ambitious destination for an intimate BYO, but my criticisms from a previous two-bell review remain the same - the kitchen's limited approach. Every entrée seemed a variation on seared fish perched over a pedestal of starch ringed by sauce. And this time, there was less consistency in cooking (overcooked striped bass, slightly stale cracklins) and seasoning (salty octopus, too much funky fish sauce in the crab soup) and a surprising overreliance on dairy richness in the sauces.

I'd still return for the $33 bargain Sunday prix-fixe, but there's now considerably more distance between the experiences at Fish and Little Fish.

In theory, Fathom should be the casual bookend to the Stollenwerk oeuvre, where Fishtown hipsters in tatts and flip-flops can grab a craft brew, a plate of cod pierogi, and a taste of Fish-lite.

I'm confident that someday it will - perhaps even as soon as the sidewalk construction is done, the picnic tables come out, and Fathom starts sending out pots of ready-for-feasting clambakes.

At the moment, though, this historic corner tappie on East Girard, which a century ago was known as Marsha's Saloon, is struggling with the kind basic cooking goofs that could sink even a menu as appealing and affordable as Fathom's small plates.

Oversalting was the biggest culprit, ruining two bowls of those Fathom fries - really a crabby twist on poutine from Montreal (where the lobster version is bisquey, not brackish). The crab cake sandwich suffered a similar fate, with such intense sodium in its crust, the sweet lumps tasted fishy.

It is helpful that Fathom, with its poured-concrete bar (great for solo dining) and high-top marble tables, is tailor-made for drinking to dilute the brine. There are some well-crafted cocktails (try the refreshing mint sweet tea) and 35 craft beers to choose from, with 10 on draft.

Had I stopped at the raw-bar platter of pristine Malpeques and fleshy Jersey littlenecks, I would have been just fine. The cold half lobster on ice - moist, sweet, and tender - was a deal for $10.

But too many of the cooked dishes that followed left me flat. The Thai steamed mussels were OK, but we've seen those at Little Fish (and everywhere else). The steamed littlenecks with chorizo were chewy and overcooked. The Jonah crab claws were inexplicably bland, especially considering they were bathed in garlic butter.

How could a lobster grilled-cheese sandwich fall short? Just smother a quarter-pound of sweet shellfish in tasteless low-grade fontina. Even the deep-fried nuggets of crab Louie were an unexpected letdown, the crustacean's delicacy erased by the fryer's heat and too much spicy mayo. The thickly crusted "chicken fried" oysters were turning to Sog City by the time they landed - though I loved the Mexican corn-and-potato salad on the side. Speaking of sides, the tempura-fried cauliflower was more memorable than the crab and oysters combined. It's not the ideal effect, I suppose, unless your gastropub has a "cabbage" theme.

There were some other notable bright spots. The smoked marlin tacos should become an instant warm-weather hit, the soft tortillas topped with cool flakes of cherry-smoked fish dabbed in mayo and the tang of house-pickled jalapeños. The smoked salmon-pumpernickel crouton salad with arugula and pickled cherry tomatoes was a refreshing take on panzanella. And the cod pierogi were everything I'd expect Stollenwerk bar food to be: a clever twist on a neighborhood classic, with delicate half-moon dumplings that were stuffed with fresh cod and potatoes, then browned in butter and house-cured bacon.

I hoped for the same inspiration from a special fish-and-chips made with shad, a catchy ode to that swimming beacon of spring. What we got instead were three measly strips of mushy fish encased in a wrinkled gray sock of crust that had long lost its crisp, if it had ever had one. It was also salty - no surprise.

Except that I was surprised, given Stollenwerk's track record. Then again, he wouldn't be the first big-eyed chef to get overeager at the proverbial fish fry of rapid restaurant success. Let's hope he quickly regains some focus, and reels in the kitchen discipline that made him a seafood star to begin with.

Contact Craig LaBan at claban@phillynews.com.