The word leatherfish is playable in Words With Friends™, no blanks required. Because it is longer than 7 letters, you would have to play off an existing word or do it in several moves.
Words With Friends™ Letter Score: 19
Highest Scoring Words With Friends™ Play In The Letters
Seven Letter Word Alert: (59 words)
aeriest, atheise, elaters, faeries, fairest, falters, fathers, feather, felsite, fertile, filters, flasher, freesia, hafters, halites, halters, hastier, healers, healths, hearths, heaters, heather, hefters, heftier, heifers, herself, lathers, leafier, leather, lefties, lifters, ratfish, realest, realise, realist, refiles, reflash, reflate, reflies, reheats, relates, reliefs, reshift, retails, retiles, saltier, sealife, seriate, shalier, sheathe, shelter, shifter, slather, slatier, slither, stealer, sterile, stifler, trifles