The Fisher Achievements, especially the Resplendent Tacklefiend's Rod are a much larger undertaking than all other Relic Tools and will require weeks of work to obtain. You will require an combination of resources to properly catch each required fish.

The Fish that do contribute to the Fishing Log include Ocean Fishing, Big Fish as well as Spearfishing.

Some rare fish can only be caught in Housing areas.

You will require a number of various different Fishing Baits and Lures to catch specific fish.

Be sure to stock up on High Quality Cordials and Hi-Cordials also.

FFXIV Angler is the absolute best resource for Fishing and will be an invaluable tool in revealing the conditions and bait required for every fish.

Carbuncle Plushie will help you track which fish are currently active, determined by Weather and Time conditions.

Lulu's Ocean Fishing Tracker will tell you which bait and Fishing Objectives for each voyage in real time. Very useful for catching Ocean Fishing exclusive fish that require the Fisher's Intuition buff.

The majority of fish do not have any specific conditions other than the Bait or Lure used to catch them, fish marked in the Fishing Log with ??? for Weather and Time conditions are likely to be Big Fish with very specific conditions to be caught. Once conditions have been met for Big Fish, you may receive a notification such as "A massive shadow slides across the floor", the catch is not guaranteed even if all the conditions have been met so don't give up or be discouraged if you miss the fish or do not even get a bite (especially after using Surface Slap to remove undesirable fish).

It is recommended to use Yakow Moussaka HQ food for the GP boost enabling you to have 950+ starting GP as a Fisher

For Fish that require you to Mooch another fish; fish normally until you catch the desired fish, use Mooch if it is Large, use Mooch II if it is not Large.

If Mooch II is on cooldown and you catch a Normal-sized fish, use Prize Catch -> Identical Cast to catch the same fish and guarantee it is Large for a subsequent Mooch.

Prize Catch -> Identical Cast -> Mooch -> Mooch II can also be employed for double Mooch fish.

If opting to use Patience II; instead of Hook, use the appropriate Hookset action (Precision for ! / Powerful for !! or !!!) to increase the likelihood of the subsequent fish being Large. Some !!! fish require the Precision Hookset so it is always good to double-check with Carbuncle Plushie.

Be sure to set your own Battle Effect Settings to Show All in the Character Configuration -> Control Settings -> Character tab to enable the Bite indicators (! / !! / !!!)

Some Fish caught via Spearfishing will require you to catch a specific number of another fish in the location to uncover their [Swimming Shadows] Spearfishing node. An example is the Bothriolepis in Lakeland, which requires you to initially catch 10 Noblefish.

There are helpful YouTube videos for every single Big Fish as well as other elusive fish so be sure to do some research if you find yourself losing momentum while working on the Fishing Achievements.