Josh Niland is a food critic's worst nightmare. What I eat at his newly opened Paddington fish restaurant will not be what you eat. Why? Because he changes the menu daily, if not hourly. Why? Because it's fish, and you can't catch fish to order.

The earnest young Niland, who honed his skills with Steve Hodges at Fish Face, is serious about fish, installing a static coolroom in which whole fish are hung and aged to intensify flavour. He's so serious about fish, there isn't a scrap of meat on the menu.

He's also serious about cooking head-to-tail, serving john dory liver on toast; or deep-frying mulloway scales to scatter over salt-baked pumpkin. Or saving up Petuna smoked ocean trout cheek, belly and tail trimmings for a slow confit before turning them into a light and lovely mounded rillettes ($16), covered with crisp radish scales like a reclining pink armadillo.

If there is anything resembling a cold Ballina spanner crab entree ($24), order it. It might come as mine did, the hand-picked white meat tucked into a pristine orange shell with a rich coral sauce made from the crab's innards. Pile it onto fresh, dark Berkelo malt bread, close your eyes, and suddenly you're wriggling your toes in the sand, seagulls squawking in the air, instead of sitting at a bare table in a slightly austere long shopfront space bordered by exposed convict bricks and the golden glow of Sydney sandstone.

Another highlight is grilled Spencer gulf calamari ($22); a laidback tumble of legs and squiddy bits, saltbush and julienned pickled kohlrabi, that's just as light and lively.

But you can't come to a fish restaurant and not have fish; and the fish at Saint Peter is seriously good.

A meaty cross-section of pot-roasted john dory ($36) is served with buttery juices and sweetly caramelised cloves of garlic – lots of 'em.

If you like your fish skin-crisped, look for something like the wild barramundi from Mackay ($36) – a world apart from the farmed stuff – pan-seared under a fish weight, so the skin is so crisp you could use it to cut through the milky, sea-sweet flesh. Accompaniments are considered, umami-pimped vegetables; in this instance, a whole onion, slow-cooked in the dying embers of the charcoal and bathed in dashi-like juices.

The one-page wine list leans towards fresh and fruity whites including a complex, intense 2015 Bress fume blanc from Macedon ($16/$79), but this is one fish restaurant in which you can also drink lighter reds, such as Geelong's plummy 2013 Farr Rising Gamay ($75).

With young-gun pastry chef and partner Julie Niland on board, desserts are simple but superbly executed. The classic tarte citron ($16) is virtuosic, shimmering under its mirror glaze.

It's all very fresh, fresh, fresh – the fish, of course, but also the thinking, the single focus. Saint Peter the man was an apostle fisherman who left his black thumbprint on the side of the john dory, the fish the French call saint-pierre. Saint Peter the restaurant houses a thoughtful, considered and driven young chef, who is clearly stamping his own thumbprint on fish dining in this country.

THE LOWDOWN
Best bit: Fish taken to great heights.
Worst bit: Thin paper napkins.

Terry Durack is chief restaurant critic for The Sydney Morning Herald and senior reviewer for the Good Food Guide. This rating is based on the Good Food Guide scoring system.