Sweden is a hotbed for startups, having spawned success stories like Spotify and Skype.

One Stockholm-based startup you probably haven't head of is Fishbrain, a social networking app for anglers.

The "Instagram of fishing" lets users share information about the fish they've caught, like where they caught them, what type of bait they used, and how big a fish they managed to snag.

The app can predict the optimal time and place to catch a particular species of fish at any given time and tell you which bait to use. Parts of it look pretty similar to Instagram, especially the section which lets users follow other anglers. Fishbrain also lets people compete against friends, family and their fellow fishing club members to reel in the biggest fish they can catch in any given species.

The app serves a lucrative market: In the US, where 75% of the app's 1 million users are now based, anglers spend $48 million (around 30 million) a year on bait alone.

Fishbrain has 12 employees, and is currently wrapping up a Series A round. It raised $2.4 million in a 2014 seed round led by Northzone and Active Venture Partners.

The company's CEO Johan Attby told us that fishing has missed out on the technological developments that have come to other hobbies.

"Runners can track their routes, golfers can analyse their swings, but before FishBrain came along, there was no equivalent for anglers," he said.

Attby describes himself as "super bullish about vertical social networks in general".

While we're not all going to split off from Facebook or Instagram based on our hobbies, Attby believes that there is a market for smaller social networks where, for example, your friends who like gardening can show off their award-winning roses, or your birdwatching friend can upload a picture of yet another bird.

"While exploring this, I found out that sport fishing is the worlds biggest hobby and a greenfield for building a vertical social network for. Its probably also the best possible fit for a social network too, because anglers love to brag about their catches and trips."

Attby says the app has recorded a lot of monster catches, including one Greenland shark that weighed hundreds of kilos.

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