If you want to take advantage of all fishing nodes in the Elderwood of Palia, you're going to need to complete the main quest Something Fishy. Beginning after The Nature of Shadows, finishing the quest will give you the ability to fish at infected nodes. This is how to complete Something Fishy and catch infected fish in Palia.
Palia Something Fishy Walkthrough
If you choose to catch fish for Subira as additional specimens, Something Fishy will start right after you finish The Nature of Shadows. If you picked a different method, Something Fishy can start after you complete Bugging Out or Shot in the Dark.

When you actually do start Something Fishy, you'll be directed to Einar. You can find him at the Kilima Dock or in his abode. In the spirit of saving the fish from the melancholy he senses off you, he asks for some samples.
- Fish from the Elderwood x3
- Infected Essence x10
These fish can be of any rarity and they don't have to be starred. The only requirement is that they are from the Elderwood. The De Mer Dock on the west side of the region is prime for fishing.
Once you've caught the fish, return to the Galdur. Upon examination he'll design a new lure titled the Elderwood Lure for you to use. He'll give you the first lure free as well as the crafting recipe.
Elderwood Lure Recipe

The Elderwood Lure is the most "expensive" item to craft that's specific to the forest. It needs four items instead of three and uses the most Infected Essence, even when compared to buying Tamala's Elderwood Potion.
- Silk x20
- Palium Bar x1
- Ogopuu Skin x3
- Infected Essence x50
If this wasn't the method you initially chose for Subria's extra samples the quest will end. If this is for Subria, the quest will continue to the second stage. Now you'll need to find infected fishing nodes around the Elderwood. Again, De Mer Dock is great for this. There are typically 4-5 nodes at a single time there, increasing your odds of some being infected. You can tell the difference by the purple and black goop that bubbles out of the node.
You can also use the Tuning Fork to point you towards any nodes as you explore the area. This doesn't guarantee they are infected, but gives you more chances to find them.
- Infected Fish from the Elderwood x5
- Infected Essence x50
You must have the lure equipped to fish at the infected nodes. This can make catching rare and epic fish that much harder since safe zone size and speed boosts from lures won't be in effect.

When you have the five fish, meet Subira in the Elderwood Central Stables. After a brief dialogue the quest will end and you'll be rewarded with 25 Renown. You want to speak with her again to begin the two other quests allowing you to catch and hunt infected Elderwood critters:
- Bugging Out
- Shot in the Dark
The next quest has you tracking a much different animal instead of focusing on the infection found in the forest. Since you'll go to different areas of the Elderwood, I suggest completing both quests before starting One Step Behind.