Last weekend was warm and sunny, and visions of cherry blossoms danced in our heads. Today the weather's unpredictable as usual. But there's a place immune to the inconstancies of March, a place where the temperature is never less than 74 degrees and nature's paintbrush doesn't know the muted greens and browns of winter.

Bubbling noises from 50 fish-filled tanks welcome us into the Tropical Lagoon Aquarium. Yellow-breasted songbirds chirp in the window and a blue-fronted Amazon parrot, gurgling "Arturo, Arturo," nods down from the top of his cage.

Arthuro is a frequent boarder in the store and a favorite of Joan Holtgraver, her staff and her customers. On cold days I wish I were a boarder in this warm, well-lighted place. It's another world and you don't have to buy a plane ticket to get there.

Many of Holtgraver's customers come just to look. We're no exception, although today I also want to buy gerbil food. My son hands me his hat and gloves, then hurries towards the 135-gallon saltwater aquarium that faces the entrance. He's six and full of instructions for his little sister Maro on where to look for the sea horses that live in this tank. They like to hide in the branches of the coral where they anchor themselves with their long curled tails and sway softly in the water.

Small sister can't find the sea horses but she discovers a new creature, an underwater version of a gigantic daddy-long-legs.

"That's an arrow crab," Dimitri tells her, to my surprise. I didn't know he knew. The creature prances on arched limbs over a delicate white-tipped anemone and the children exclaim over the jerky movements of its feeders. Behind it float translucent jade green tentacles of a larger anemone.

The price tabs on this tank indicate that it's inhabited by, besides the arrow crab, pencil urchins, serpent stars, maroon clowns, feather dusters, Atlantic and cluster and carpet anemones, flame scallops and banded coral shrimp. If you don't know what is which -- and we don't -- guessing can be more fun than knowing.

Customers of all ages are fascinated by this tank, but usually for different reasons. For adults, the attraction is the exquisite beauty of the saltwater plant and animal life. For kids, it's the oddity of the creatures and the continuing drama of their interaction.

"Hey, that purple thing moved. I think it's trying to get that other orange and black thing."

"Maybe. But the orange and black thing's mouth is open. See those little teeth?"

Until recently marine aquaria were not generally available and difficult for home enthusiasts to maintain: sea water was hard to duplicate, tank metal corroded, and coral fish in captivity died of diseases that weren't understood. Now new products like synthetic sea water and all-glass tanks have been developed and there are books to keep hobbyists informed of the disposition and care of marine life.

The Tropical Lagoon has been at 7710 Woodmont Avenue in Bethesda for three and a half years. In that time freshwater fish have remained the best item, but saltwater sales have steadily increased. The store maintains 13 marine tanks.

My daughter finds one at her three-year-old eye level and calls me to take her coat and see the "twiddle bugs from Sesame Street." These turn out to be blue-dotted fish a cubic inch in size and shape. Four rapidly oscillating fins propel them abruptly forth and back. The tab on the glass identifies them as cowfish.

Elsewhere Dimitri finds a bizarre and aptly named spiney boxfish, and I see a majestic angel so intensely blue that its yellow tail is startling. The blue damselfish are lovely, too; and so is an orange and purple royal gramma. The fish dart, some hover, some stare back with unblinking eyes. They are like living works of modern art, glowing in banded, striped and Morse-coded fluorescent hues.

Against the far wall are the parrots. Mean Green, a blue-crowned Amazon, presides. Beneath his ceiling-hung cage are rows of parakeets. There's also the reptile contingent, and even a tarantula. Last month we saw a hairy Haitian tarantula; today it's a red-legged specimen. Holtgraver says the store sells an average of two a month.

"They make interesting conversation pieces and less dangerous than most people realize," she says.

Fortunately, my spider-loving son doesn't hear this. He's busy watching a customer buy some of the live crickets Hotgraver sells for tarantula food.

My daughter thinks the baby boa looks hungry. Once a week he's fed an infant mouse called a pinkie. Maybe today's the day. A Savannah Monitor in the next tank is luckier; he gets a pinkie every two or three days.

The guinea pigs are next and Maro stops to converse with them. Like most visitors here, large and small, she has no inhibitions about talking to the animals.

By the time I buy the gerbil food, the kids have circled the store twice and I am holding a great pile of coats and hats and gloves. A boy behind us with a double-dipped cone from the ice cream parlor downstairs complains that his ice cream is melting.

The words warm my heart.