There are plenty of whole families (or even orders!) of fish that are rarely mentioned and are unfamiliar to most - this is a non-exhaustive list
Lampreys of the families Geotriidae and Mordacidae are very obscure compared to the better-known Petromyzontiidae lampreys.
Sharks and rays:
Brachaeluridae (blind sharks)
Parascylliidae (collared carpetsharks)
Pseudotriakiidae (false catsharks)
Echinorhinidae (bramble sharks)
Platyrhinidae (fanrays)
All skates of the order Rajiformes except Rajidae (hardnose skates)
Zanobatidae (panrays)
Hexatrygonidae (Sixgill Stingray)
Plesiobatidae (Giant Stingaree)
Ray-finned fishes
- Elopidae (tenpounders)
- Notacanthiformes (deep sea spiny-eels and halosaurs)
- Protanguillidae (Palauan Primitive Cave Eel)
- pretty much all members of the Anguilliform suborder Anguilloidei (sensu Near & Thacker) except the Anguillidae (freshwater eels) and Eupharyngiidae (Gulper Eel)
- All members of Gonorhynchiformes except the Milkfish - this order also includes Kneriidae (shellears), Gonorhynchidae (beaked salmons) and Phractolaemidae (hingemouth)
- All members of Argentiniformes except the Pacific Barreleye - this order also contains Argentinidae (argentines), Microstomatidae (pencilsmelts), Bathylagidae (deepsea smelts), and the other members of Opisthoproctidae (barreleyes)
- All members of Osmeriformes except Osmeridae (smelts) - this order also contains Plecoglossidae (Ayu, well-known in Japan but obscure elsewhere), Salangidae (noodlefishes) and Retropinnidae (New Zealand smelts)
- Gonostomatidae (bristlemouths) and Phosichthyidae (lightfishes, although this family is probably polyphyletic)
- Atelopodidae (jellynoses, the only extant family in Atelopodiformes)
- Paraulopidae (cucumberfishes)
- Chlorophthalmidae (greeneyes)
- Notosudidae (waryfishes)
- Scopelarchidae (pearleyes)
- Paralepididae (barracudinas, probably polyphyletic)
- Omosudidae (Hammerjaw)
- Neoscopelidae (blackchins)
- Veliferidae (velifers)
- Radiicephalidae (tapertails)
- Lophotidae (crestfishes)
- The entire order Percopsiformes may be familiar to freshwater fishermen in North America but is obscure elsewhere - contains 3 families, Percopsidae (Trout-perch and Sandroller), Aphrododeridae (Pirate-perches) and Amblyopsidae (Cavefishes)
- All Zeiformes except Zeidae (typical dories) - also includes Cyttidae (lookdown dories), Oreosomatidae (oreos), Grammicolepididae (tinselfishes), Zeniontidae (dwarf dories) and Parazenidae (parazens)
- Diretmidae (spinyfins)
- Melamphaidae (bigscales)
- Gibberichthyidae (gibberfishes)
- Hispidoberycidae (Bristlyskin)
- Stephanoberycidae (pricklefishes)
- Kurtidae (nurseryfishes)
- Trichonotidae (sand-divers)
- Xenisthmiidae (collared wrigglers)
- Ariommatidae (ariommas)
- Amarsipidae (Amarsipa)
- Caristiidae (manefishes)
- Draconettidae (slope dragonets)
- Phallostethidae (priapumfishes) and Dentatherinidae (Tusked Silverside) - combined by Near & Thacker into a more inclusive Phallostethidae
- Isonidae (surf sardines)
- Congrogadidae (eel-blennies) - formerly included in Pseudochromidae (dottybacks) but genetic evidence suggests that eel-blennies are not closely related to dottybacks
- Plesiopidae (roundheads) outside of Australia except the Comet/Marine Betta
- Lactariidae (False Trevally)
- Leptobramidae (beachsalmons)
- Polynemidae (threadfins)
- Acanthistius (wirrahs and koesters) - currently assigned to the familiar Anthiadidae, but genetic evidence suggests that they would be better placed in their own family
- Bembropidae (duckbill-flatheads)
- Niphonidae (Ara Grouper) - previously assigned to Epinephelidae (and before that, Serranidae)
- Percophidae (Brazilian Flathead)
- Bovichtidae (thornfishes), perhaps more familiar to tidepoolers in southern Australia
- Pseudaphritidae (Congolli/Tupong)
- Eleginopsidae (Patagonian Blenny)
- Harpagiferidae (plunderfishes)
- Normanichthyidae (Mote Sculpin)
- Congiopodidae (Horsefishes)
- Agonidae (poachers)
- Bathymasteridae (ronquils)
- Zaproridae (Prowfish)
- Ptilichthyidae (Quillfish)
- Dichistiidae (galjoens) - familiar in South Africa, obscure elsewhere
- Caesioscorpididae (Blowhole Perch)
- Parascorpididae (Jutjaw)
- Centrogenyidae (false scorpionfishes)
- Cheimarrichthyidae (Torrentfish)
- Leptoscopidae (southern sandfishes)
- Acropomatidae (lanternbellies)
- Ostracoberycidae (shellskin alfonsinos)
- Symphysanodontidae (slopefishes)
- Epigoniidae (deepwater cardinalfishes)
- Howelliidae (oceanic basslets)
- Dinolestidae (Longfin Pike)
- Banjosidae (banjofishes)
- Synagropidae (splitfin ocean-basses)
- Creediidae (sand-burrowers)
- Dinopercidae (Cavebass and Chapin's Barred Seabass)
- Emmelichthyidae (rovers)
- Leiognathidae (ponyfishes and slipmouths)
- Callanthiidae (splendid-perches and groppos)
- Cepolidae (bandfishes)
- Lophichthyidae (Boschma's Anglerfish)
- Pretty much all families of Ceratioidea (bathypelagic anglerfishes) except Himantolophidae (footballfishes) and Melanocetidae (black seadevils)
- Triodontidae (Threetooth Puffer)
- Triacanthodidae (spikefishes)