Notes on acquiring these:

• Most of these are seasonal companions. The <a href="/wiki/Prismatic_Squidling" title="Prismatic Squidling">Prismatic Squidling</a>, <a href="/wiki/Unerring_Elver" title="Unerring Elver">Unerring Elver</a>, and (with a friend) <a href="/wiki/Voracious_Lamp-Eye" title="Voracious Lamp-Eye">Voracious Lamp-Eye</a> are available during a <a href="/wiki/Whitsun" class="mw-redirect" title="Whitsun">Whitsun</a> with <a href="/wiki/Pelagic_Egg" class="mw-redirect" title="Pelagic Egg">Pelagic Eggs</a>, with a friend a <a href="/wiki/Copper-Speckled_Crustacean" title="Copper-Speckled Crustacean">Copper-Speckled Crustacean</a> can be acquired with <a href="/wiki/Aged_Egg" class="mw-redirect" title="Aged Egg">Aged Eggs</a>, and at <a href="/wiki/Christmas" class="mw-redirect" title="Christmas">Christmas</a> a <a href="/wiki/Dark-Carapaced_Crustacean" title="Dark-Carapaced Crustacean">Dark-Carapaced Crustacean</a> is easy to get by <a href="/wiki/Feed_it_to_a_Talkative_Rattus-Faber" title="Feed it to a Talkative Rattus-Faber">endangering the life of an eighty-pence rat</a>.
• If you're a FATE-spender, you can add the <a href="/wiki/Gilded_Crustacean" title="Gilded Crustacean">Gilded Crustacean</a> (Whitsun + <a href="/wiki/The_Empress%27_Shadow" title="The Empress' Shadow">The Empress' Shadow</a> + <a href="/wiki/Sinning_Jenny%27s_Finishing_School_(Guide)" title="Sinning Jenny's Finishing School (Guide)">crit success on an AotRS 3 check</a>) and the <a href="/wiki/Mostly_Stuffed_Bound_Shark" title="Mostly Stuffed Bound Shark">Mostly Stuffed Bound Shark</a> (Christmas + <a href="/wiki/Incarnadine_Fur_Robe" title="Incarnadine Fur Robe">Incarnadine Fur Robe</a>) to this list. (But given that the Bound Shark is of no other distinction and the second-tier gift it unlocks isn't mechanically interesting either, there are much better uses for the Robe.)
• If you aren't going to wait for the relevant time of year (and correct egg type, which will only happen every other Whitsun), you can use <a href="/wiki/Live_Specimen" title="Live Specimen">Live Specimens</a>, which are grindable by <a href="/wiki/On_a_Heist_(Guide)" title="On a Heist (Guide)">doing heists</a> of <a href="/wiki/The_Circumspect_Envoy%27s_Townhouse" title="The Circumspect Envoy's Townhouse">The Circumspect Envoy's Townhouse</a> and <a href="/wiki/Deliver_the_documents_to_the_Glass" title="Deliver the documents to the Glass">sending that information to the Glass</a>. If you have a decent source of <a href="/wiki/Casing..." title="Casing...">Casing...</a>, this is a perfectly acceptable way to go about things.
• If you are a Monster-Hunter <a href="/wiki/A_Giant_Angler_Crab" title="A Giant Angler Crab">who goes zailing a lot</a>, you might already have a stock of <a href="/wiki/Deep-zee_Catch" title="Deep-zee Catch">Deep-zee Catches</a> to offload, and here's as good a place as any. (It's not worth aimlessly zailing hoping for the relevant card to come up, though.)
• If you are so far into the game as to have access to <a href="/wiki/Khan%27s_Heart" title="Khan's Heart">Khan's Heart</a>, you can just buy <a href="/wiki/Deep-zee_Catch" title="Deep-zee Catch">Deep-zee Catches</a> for 2 <a href="/wiki/Assortment_of_Khaganian_Coinage" title="Assortment of Khaganian Coinage">Assortment of Khaganian Coinage</a> each at the <a href="/wiki/Midnight_Market" title="Midnight Market">Midnight Market</a>. If you already have a source of Khaganian Coinage, this is the easiest way for a lategame player to just have done with it. (If you aren't already well on the way to entering Khan's Heart, just do the Envoy heists.)
• All the Goldfish are too slow to use. 2-4 research is honestly pitiful.