A number of the booms in Japan, including Tamagotchi — basically a virtual pet that grew on a computer screen — and the fanciful cartoon characters of Pokémon, have made their way across the Pacific and swept up American children, too.

Image Hirofumi Sasaki, a pet store owner in Hiroshima, has seen so many defective dogs that last year he converted an old bar into a hospice to care for them. So far he has taken in 32 dogs, though only 12 have survived. Credit... Masafumi Yamamoto for The New York Times

The affection for fads in Japan reflects its group-oriented culture, a product of the conformity taught in its grueling education system. But booms also take off because they are fueled by big business. Companies like Sony and Nintendo are constantly looking to create the next adorable hit, churning out cute new characters and devices. Booms help sustain an entire industrial complex, from software makers to marketers and distributors, that thrives off the pack mentality of consumers in Japan.

The same thing is happening in Japan’s fast-growing pet industry, estimated at more than $10 billion a year. Chihuahuas are the current hot breed, after one starred in the television ads of a finance company. In the early 1990s, a TV drama featuring a Siberian husky helped send annual sales rocketing from just a few hundred dogs to 60,000; sales fell when the fad cooled, according to the Japan Kennel Club. The breed took off despite being inappropriately large for cramped homes in Japan.

The United States also experiences surges in sales of certain breeds, and some states have confronted “puppy mills” that churn out popular breeds by enacting “puppy lemon laws” that prevent breeders from selling diseased animals.

But in Japan, the sales spikes are far more extreme, statistics show. The kennel club says unethical breeders try to cash in on the booms, churning out large volumes of puppies from a small number of parents. While many breeders have stuck to healthy mating practices, the lure of profits has attracted less scrupulous breeders and led to proliferation of puppy mills.

Some veterinarians and other experts cite another, less obvious factor behind widespread risky inbreeding in Japan’s dog industry — the nation’s declining birthrate.

As the number of childless women and couples in Japan has increased, so has the number of dogs, which are being coddled and doted upon in place of children, experts say. In the last decade, the number of pet dogs in Japan has doubled to 13 million last year — outnumbering children under 12 — according to Takashi Harada, president of Yaseisha, a publisher of pet industry magazines.