This figure is the Japanese Dolly Varden (also known as Miyabeiwana or Miyabe Char in Japan), Salvelinus malma miyabei, a Secret Figure from the first series revised release (so, the third release of series 1 for those keeping track). I believe it is numbered #17 in the set, although it is based on model #2.
All Salvelinus Reviews
White-spotted Char (Freshwater Fish Pictorial Book, Series 1, revised by Yujin)
4.8 (4 votes)
This figure is the White-spotted Char (also known as iwana in Japan), Salvelinus leucomaensis, number 02 from the first series. This salmon and trout relative is a fish found in East Asia, and can be landlocked or ocean-running. As with many Japanese fish models (though not all) it is widely fished for.