I'm not sure specifically as I haven't read this exact story, but it could be a fisherman. A fisherman is a common character in stories related to trout, as they often interact with the trout.
It's also possible that there is an old man. An old man could be a character who has a lot of knowledge about trout, like where to find them, their behavior, etc. He could be a mentor - like figure to the younger characters in the story, teaching them about the trout and the importance of nature.
Chapter 437, "A Gentleman's Revenge is Not Too Late Even After Ten Years!", is the clearest early answer because it turns Sister Li's situation into a concrete plot event. It opens with [What's happening, why did a group of people suddenly show up and...
Chapter 780, "There's Someone in Your Room!", is the clearest early answer because it turns Feng Shui's situation into a concrete plot event. The setup is Sister Li was a bit confused., but the pressure keeps building through Do romantic relationships also depend on your living environment?.
Chapter 822, "The Yu Family Gave Too Much", is the clearest early answer because it turns Yu Qing's situation into a concrete plot event. The chapter gives readers a real answer by opening on Jiang Li entered the reception hall, which was already quite crowded.
Chapter 457, ""Back Against the Wall", is the clearest early answer because it turns Zhao Lang's situation into a concrete plot event. The chapter turns that into something concrete by moving from Five minutes later, he stared at Yu Li with his twitching mouth...
Chapter 705, "Is She Her Own Destined Noble Person?!", is the clearest early answer because it turns Yu Fei's situation into a concrete plot event. The chapter turns that into something concrete by moving from He Wen was made to laugh by Bai Lu.
Chapter 605, "The Plan to Surround and Annihilate Team Q Commences!", is the clearest early answer because it turns Shang Shaojing's situation into a concrete plot event.
Chapter 466, "Are There Really Wild Boars?!", is the clearest early answer because it turns Zheng Xun's situation into a concrete plot event. The chapter turns that into something concrete by moving from The lady sure acts like a lady, even in 'Wilderness Survival' she...
Chapter 557, "Where Did This Rotten Fish Come From, It's Disgusting", is the clearest early answer because it turns Sister's situation into a concrete plot event. A useful checkpoint is the way the scene starts with The triple broth was almost done, Jiang Li dusted her hands off and...
Chapter 619, "The Feast of Fish CP Is Indeed Real!", is the clearest early answer because it turns Jiang Li's situation into a concrete plot event.
Chapter 754, "Evil Can Never Defeat Justice", is the clearest early answer because it turns Jiang Li's situation into a concrete plot event. A useful checkpoint is the way the scene starts with After the court trial ended, everyone immediately threw a party for...