I caught this fish yesterday in St. John river in Canada. My father and I don't know what it is.
Fish like this have been caught recently (this Summer). Apparently, the fish was caught using worms.
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It appears to be a smallmouth bass based on this MN DNR link.
Adding to @acpilot's answer, it appears New Brunswick, while not part of the native range of the smallmouth bass, is part of the expanded range of the fish. That further leads to a possible confirmation of the species. Here is the native and expanded range of the species in the United States according to the US Geological Survey:
This map doesn't show the expanded range into Canada, but this paper from the Canadian Manuscript Report of Fisheries and Aquatic Sciences describes the species in Canada:
T.G. Brown, B. Runciman, S. Pollard, A.D.A. Grant, and M.J. Bradford: "Biological Synopsis of Smallmouth Bass (Micropterus dolomieu)"  Canadian Manuscript Report of Fisheries and Aquatic Sciences
Specifically, the authors include this map of the native and expanded ranges of the species in section 2 of their paper, "Distribution", which shows the species in New Brunswick: