3 letters:
ish

4 letters:
bish, dish, fish, gish, isch, kish, lish, mish, rish, tish, wish, wisz

5 letters:
bisch, blish, brish, crish, disch, drish, fisch, glish, kisch, klish, knish, misch, omish, phish, risch, shish, slish, swish, tisch, trish, whish, wisch, wishe, yeshe

6 letters:
achish, assish, delish, episch, frisch, guiche, irisch, krisch, ladish, latish, mclish, mcnish, offish, squish, unwish

7 letters:
affiche, badisch, barfish, basisch, batfish, boxfish, bugfish, catfish, codfish, commish, demisch, dogfish, dunfish, finfish, flyfish, foxfish, frische, garfish, gibfish, glofish, go fish, henfish, hogfish, icefish, inkfish, jagdish, jawfish, jewfish, komisch, logisch, magisch, mcclish, mudfish, nephish, netfish, oarfish, oilfish, penfish, pigfish, pupfish, ratfish, redfish, sawfish, sunfish, tubfish, twofish, waifish, wheyish, witfish, wolfish

8 letters:
baitfish, billfish, blobfish, bluefish, boarfish, bonefish, burrfish, cavefish, chemisch, chenfish, coalfish, cod-fish, crawfish, dandyish, dealfish, drumfish, fallfish, filefish, firefish, flatfish, fly-fish, foolfish, frogfish, gamefish, goatfish, goldfish, handfish, hawkfish, headfish, hektisch, hornfish, jackfish, kelpfish, kingfish, klipfish, ladyfish, lionfish, lumpfish, lungfish, milkfish, monkfish, moonfish, net fish, numbfish, nymphish, odd fish, overfish, pipefish, pondfish, porkfish, prowfish, rockfish, rosefish, sailfish, saltfish, sandfish, seerfish, seirfish, snapfish, soapfish, starfish, studfish, suckfish, surffish, tangfish, tierisch, tilefish, toadfish, tokenish, wallfish, weakfish, wingfish, wolffish, wormfish, yokelish

9 letters:
akustisch, alms dish, amberfish, angelfish, beardfish, blackfish, bladefish, blindfish, bony fish, cigarfish, clingfish, clownfish, coal-fish, cold fish, conchfish, crampfish, crapefish, creekfish, crossfish, dalgleish, devilfish, driftfish, elastisch, endemisch, flamefish, flat-fish, food fish, frostfish, game fish, ghostfish, glassfish, globefish, goosefish, greenfish, guardfish, half-fish, horsefish, houndfish, icejjfish, interwish, jellyfish, jewelfish, lemonfish, moralisch, mousefish, pearlfish, pilotfish, platyfish, politisch, pollyfish, poor fish, pork-fish, praktisch, queenfish, razorfish, roundfish, sablefish, scaldfish, shanklish, sheatfish, shellfish, side dish, skullfish, snailfish, snakefish, snipefish, soap dish, spadefish, spearfish, spikefish, spoutfish, squawfish, stingfish, stockfish, stonefish, superfish, surf fish, swellfish, swinefish, swordfish, tartufish, thunfisch, tigerfish, tovarisch, trunkfish, tuna fish, ungarisch, viperfish, well-wish, whitefish, wolf fish, wreckfish

10 letters:
akademisch, allergisch, angel-fish, anglerfish, archerfish, aromatisch, barbarisch, barrelfish, battlefish, biologisch, bottomfish, butterfish, candlefish, cornetfish, cuddlefish, cuttlefish, damselfish, devil-fish, doctorfish, dogmatisch, dollarfish, dragonfish, dramatisch, elektrisch, fresh fish, frost fish, groundfish, guitarfish, lancetfish, lizardfish, muttonfish, needlefish, oysterfish, paddlefish, parrotfish, pearl-fish, petri dish, pufferfish, rabbitfish, razor-fish, ribbonfish, rough fish, rudderfish, sheathfish, shrimpfish, silverfish, sleevefish, snake-fish, spezifisch, stammtisch, still-fish, stockfisch, suckerfish, sword-fish, tanglefish, tartuffish, thing-fish, threadfish, tokhtamysh, tonguefish, weaverfish, yellowfish, young fish

11 letters:
allegorisch, anekdotisch, angler fish, australisch, automatisch, balloonfish, banana fish, basket fish, bishop-fish, bottom fish, buffalofish, butter dish, chucklefish, convictfish, creole-fish, cutlassfish, doctor-fish, dolphinfish, einheimisch, flying-fish, flying fish, frankenfish, ground-fish, harvestfish, hatchetfish, lancet fish, lanternfish, leatherfish, make-a-wish, oyster-fish, oyster fish, pragmatisch, pricklefish, quadratisch, rainbowfish, roosterfish, scum's wish, sea catfish, shrimp-fish, skilletfish, snobistisch, soldierfish, standoffish, surgeonfish, swallowfish, theoretisch, thread-fish, thunderfish, tintenfisch, tongue-fish, triggerfish, trumpetfish, vegetarisch, whistlefish

12 letters:
achromatisch, anemone fish, bellows fish, blue catfish, buffalo fish, cardinalfish, chafing dish, filet-o-fish, footballfish, handsaw fish, mosquitofish, narzisstisch, plentyoffish, rainbow fish, rock sunfish, scabbardfish, schreibtisch, scorpionfish, sea crawfish, serving dish, soldier-fish, squirrelfish, sturddlefish, sucking fish

13 letters:
alligatorfish, annabeth gish, butterflyfish, crucifix fish, ocean sunfish, porcupinefish, scorpion fish, sergeant fish, spiny dogfish, telescopefish

14 letters:
butterfly fish, dwarf pipefish, jackknife-fish, kettle of fish, lake whitefish, porcupine fish, saltwater fish, smooth dogfish

15 letters:
armored catfish, channel catfish, flashlight fish, freshwater fish, round whitefish, spotted sunfish

16 letters:
charakteristisch, electric catfish, european catfish, flathead catfish

17 letters:
atlantic sailfish, european flatfish

18 letters:
clown anemone fish, deepwater pipefish

19 letters:
biplane flying fish

20 letters:
blue channel catfish

21 letters:
monoplane flying fish, pacific spiny dogfish

22 letters:
atlantic spiny dogfish

23 letters:
american smooth dogfish

24 letters:
rocky mountain whitefish

7 letters:
cowfish

8 letters:
blowfish