Fishmeat, like all Gronckles, has a very round body and tiny wings. Yet, although they are small, they have incredible flapping velocity. As a young dragon, Fishmeat needs lots of naps and has occasionally been known to fall asleep mid-flight. Whether he's teething, eating stones, or taking naps, Fishmeat is lucky to have Fishlegs caring for him and carrying him around everywhere.
Sometime between the events of the second film and the third film, Meatlug had offspring again. It is uncertain how many she had, but Fishmeat is the only one that Fishlegs continually carried around in a pocket on the front of his flightsuit. Fishlegs even brought Fishmeat along on a dragon rescue mission. Hiccup annoyingly asked Fishlegs about "the baby" being present during the raid, to which Fishlegs responded he has been unable to find a babysitter. Later, Fishlegs and Fishmeat freed a caged Crimson Goregutter, with the baby getting very excited upon seeing the giant dragon.
After the Dragon Riders returned to Berk, Fismeat started to play with the Rescued Crimson Goregutter. The two dragons jumped around until the Goregutter hit a building, which collapsed onto others, and ultimately fell into the ocean. Toothless then roared to the pair, stopping their game. Fishmeat quickly returned to Fishlegs.
Later that day, Fishlegs brought Fishmeat to the Great Hall, where he put the baby in a chair and fed him with a spoon.
Fishmeat traveled along the rest of the tribe on their quest for the Hidden World. He was fed rocks by Fishlegs on the way, while playing on his owner's head. Snotlout commented that people who were traveling with babies were the worst, but Fishmeat didn't seem to mind him.
Fishmeat accompanied Fishlegs and the other Dragon Riders on their mission to capture Grimmel the Grisly. But when Grimmel sprung his trap, Fishmeat cried in panic before Fishlegs calmed him down. They eventually managed to escape and inadvertently left Ruffnut behind.
When all of Berk's dragons were taken to the Warlords, Fishmeat accompanied Fishlegs in the rescue before being knocked out of his pouch by an anchor. Ivar the Witless started to point his sword at the baby, only to flee in terror when the Rescued Crimson Goregutter charged in to rescue Fishmeat and Fishlegs.
Following Grimmel's defeat, the Vikings realized that they need to send their dragons to the Hidden World to live in peace. After a tearful farewell, Fishlegs placed Fishmeat in Meatlug's mouth as the two Gronckles and all of the dragons flew to the Hidden World.
Have you seen Fishmeat? I almost had him down for his nap when Tuffnut made his Zippleback fire on a bag of corn being stored nearby. The loud noises woke my baby up, and he went shooting off to Odin-knows-where! I've looked everywhere![src]
While on New Berk, Tuffnut pulls a prank by lighting some corn on fire and making an 'explosion' when the corn burst into popcorn. Fishmeat is scared off somewhere on New Berk and Fishlegs frantically asks the player to locate him. The player ultimately finds him on the edge of one of the many lakes on the island, tucks him into their satchel, and returns him to Fishlegs.
The Twins cause another ruckus on New Berk by luring countless numbers of Hobgobblers. Though not harmful, these dragons are so numerous that they were viewed as a nuisance. Fishmeat, however, found the new arrivals to be fun to play with and chased them around.
Fishmeat is a small, roly-poly baby Gronckle, with brownish rough skin on his upper body, and a softer yet bumpier yellowish underbelly, with yellow eyes — similar to some of the other baby Gronckles.
Sometimes I think I've torn off more than I can chew with this little guy. He's just so active and playful and has never-ending energy! How do other dragon moms do this? Fishmeat just doesn't want to take his nap even though it's way past his bedtime.[src]
Meatlug is Fishmeat's mother. She is very caring and protective of her son, just like Fishlegs. When the dragons left for the Hidden World, Meatlug carried Fishmeat in her mouth, due to the baby not being able to fly.
Fishlegs, for an as-yet-unknown reason, has taken a liking to Fishmeat, though Meatlug has had several previous offspring. He appears to be very maternal to Fishmeat, even naming him from a combination of his and Meatlug's names. He also claims not to have a babysitter for Fishmeat, and takes the baby Gronckle wherever he goes, even if it is somewhere dangerous.
— Fishlegs, as Fishmeat goes to play with the Goregutter
Fishmeat quickly became best friends with the Rescued Crimson Goregutter and enjoys playing with the humongous dragon. Whenever Fishmeat is threatened or in danger, the Goregutter will fiercely defend his friend.
Fishmeat is not Meatlug's first offspring seen in the Franchise. Meatlug was shown to have laid eggs in Gift of the Night Fury, which the hatched into baby Gronckles.
Fishlegs was seen carrying a toy Gronckle in a backpack during Astrid and Hiccup's wedding in How to Train Your Dragon: The Hidden World. This was meant to represent Fishmeat since Fishlegs had to let him go to the Hidden World with Meatlug.