The Albino Rhoa Feather is a rare currency item. Associations with fishing include:
In Act 1 The Mud Flats, about 1 in 150 instances will contain a special uncommon monster called Albino Rhoa.
The Albino Rhoa does not attack your character; instead, it always flees.
When killed, the Albino Rhoa drops one item: an Albino Rhoa Feather. The Albino Rhoa Feather is a currency item.
GGG staff members (especially Chris Wilson) have teased on multiple occasions that Albino Rhoa Feathers may have a secret function. Naturally, it is also possible that GGG is trolling and no special use exists. No use has been discovered yet.
Each Albino Rhoa Feather vendors for a Scroll Fragment. It has a stacksize of 10.
From datamining we know that Albino Rhoa Feathers are 'CurrencyUseType3'.
The CurrencyUseType3 classification involves items that go into special inventories. Some examples of other CurrencyUseType3 items are: Oils (=> Anointing Inventory), Scarabs (=> Map Device Inventory), Divination Cards (=> Navali Inventory), Fossils (=> Resonators, which are in fact Inventories), Breach Splinters (=> Combine into Breachstones in PlayerInventory). There are many other items in this category as well.
The classification of the Albino Rhoa Feather into this currency type implies that if a secret function exists, the secret is most likely related to either (1) placing the object into a special object/NPC inventory of some type; or (2) manipulating it within an inventory of some type.
Many years ago in very old versions of Path of Exile, Albino Rhoa Feathers were able to be placed into the Map Device. (Example screenshot from DalaiLama on 2013/08/15.) This is no longer possible.
In theory, this deprecated behaviour might explain the original classification of Albino Rhoa Feathers as CurrencyUseType3.
The secret behaviour (if any) of the Albino Rhoa Feather is an unsolved mystery.
The Albino Rhoa Feather is used in GGG media to flag a hint or a secret.
In GGG videos and screenshots, characters will often have one or more Albino Rhoa Feathers in their inventory if something else is hidden in that media. Examples of hints might include teasers of upcoming content, unreleased items, or existing secrets like Fishing Items.
The famous 'feathers.jpg' image posted by Chris Wilson is one of the earliest media hints towards the Albino Rhoa Feather itself. The filename connects Albino Rhoa Feathers to farming rhoas. Before players understood how to obtain Albino Rhoa Feathers, this was a crucial clue.
There are dozens of examples of Albino Rhoa Feathers being used in GGG media to connect to other secrets. In 'Content Update 1.0.5 Preview' from 2014/01/06, the Shadow character at the start of the video weapon-swaps away from a fishing rod, and then later opens the character inventory to reveal a few Albino Rhoa Feathers. Fishing Rods were a very recent addition at the time of this video. Another example is the April Fool's Trade Improvements Post which includes 520 Albino Rhoa Feathers. The Trade Improvements post may have been an early hint to the Writhing Jar; much later, in patch 3.9, the Writhing Jar was confirmed to be a Fishing Item via the divination card Baited Expectations.
So many more examples exist. Check out the Media Secrets section of Angler's Mate #1 for a few more.
There are multiple ways to obtain Albino Rhoa Feathers.
The easiest way to obtain an Albino Rhoa Feather is by farming Act 1 The Mud Flats and defeating the uncommon special Albino Rhoa monster. About 1 in 150 instances will contain an Albino Rhoa. Use a character optimized for movement speed or quick teleports to make this grind more reasonable.
An extremely rare Perandus chest called 'Perandus Tackle Box' contains an Albino Rhoa Feather, a fishing rod, Fairgraves' Tricorne, and Slitherpinch.
If a Gilded Fossil is applied to an item and then that item is vendored, one extremely rare outcome is a return of 5 Albino Rhoa Feathers. The Gilded Fossil itself depicts a fossilized fish.
The divination card The Fishmonger exchanges for an Albino Rhoa Feather. The Fishmonger can be found by defeating the Map Rhoa Bosses Skullbeak (Bog) or Drought-Maddened Rhoa (Arid Lake).
Albino Rhoa Feathers have existed since the Closed Beta of Path of Exile.
In the transition to Open Beta, existing Albino Rhoa Feathers from the Closed Beta persisted into the new game version. The intrepid fishing researcher ChronoExile confirmed this with Chris Wilson:
ChronoExile: I was recently told Albino Rhoas were added in the game since closed beta, is this true? Additionally, did the feathers carry over from closed beta the same way Demigod's did?
Chris Wilson: Yes, the Albino Rhoa was added to the game very early on. The feathers silently persisted into the Open Beta in the same way Demigod's Triumphs did. Very astute of you to notice
A common misconception is that Albino Rhoa Feathers were used in the Bestiary League beastcrafting recipe. This is false. In fact, it was the captured Albino Rhoa itself which was used in that recipe, not the feather. The recipe guaranteed a number of white sockets on the item based on the number of captured Albino Rhoas consumed.
There is some evidence that the Albino Rhoa Feather is not related to obtaining white sockets. On 2014/02/28 in the Sacrifice of the Vaal article, Chris Wilson wrote "Corruption is currently the only way to obtain white sockets". (This statement was made before other methods of obtaining white sockets were released.) Since Albino Rhoa Feathers existed prior to the Sacrifice of the Vaal article, Chris's comment appeared to rule out the possibility that Albino Rhoa Feathers could somehow be used to create white sockets at the time.
The notorious forum troll MonstaMunch often spread deliberate misinformation about Albino Rhoa Feathers. Monsta was clever enough to pepper forum posts with small truths, causing some players to see the lies as more believable. Be careful in your research: most of what Monsta wrote is intended to mislead you and waste your time.
Vendoring a full inventory of Albino Rhoa Feathers does not result in anything special. Over the years researchers have performed thousands of other vendor recipe experiments involving Albino Rhoa Feathers. Nothing has ever been discovered -- but the possibility space is so gargantuan that it is always possible something has been overlooked.
The fishing rod prefix 'Alluring' with value 1 results in the modifier 'Rhoa Feather Lure'.
In the secret "Catch These Fish" achievement, one of the Unique Fish names is Tuatini, Rhoa Hunter. Tuatini is the Māori word for Carcharhinus brachyurus, the bronzewhaler shark.
In very old versions of Path of Exile, vendoring a fishing rod would return an Albino Rhoa Feather. This is no longer true. The behaviour seems to have been removed sometime after 2014 (1.0.6).
The brand new Demigod's Authority sword Item Rarity aura effect displays coins and feathers.