The unusual catch has surprised researchers, as the fish is usually not found so far north is such great numbers.
"An unusual and exciting catch," Leif Nøttestad, researcher at the Institute of Marine Research in Berge, told Norway's TV2 broadcaster. "The reason why it has come is that there is a lack of space in the Mediterranean, the Atlantic, and the Black Sea, where it usually is found."
Bonitos are not an unusual fish, and they are found in many locations in the Atlantic, ranging from Nova Scotia to Port Elizabeth in South Africa. But they seldom travel as far north as Oslo.
In the Mediterranean, the fish is a popular dish, similar to Mackerel in texture and flavour, But they are used only as bait in other regions, as their flesh is considered too oily.
"It was incredibly strong and pulled my line out several times," Stian Wahlberg Kristiansen, who caught a bonito in the Oslo Fjord, told the channel. "We were clueless. We had never seen a fish like that before. My friend was ecstatic when we understood that the fish was of an unusual species."
Nøttestad said that bonito was extremely challenging for recreational fishermen.
"It's like a little torpedo. If you are lucky enough to get one hooked, remain calm and keep the line tight," he advised. "Don't panic."