Fish

three fish interchangeably posed

Fish may be borne fesswise: naiant (horizontal) or  counter-naiant   (horizontal reversed); in pale: hauriant (vertical head to chief point) or uriant (vertical head to base); embowed and interchangeably posed.

The heraldic fish, regardless of their biological classification, are as follows:

Barbel, Chalbot, Conger, Dolphin, Herring, Luce, Roach, Trout and Whale

When no particular variety is specified, the charge is blazoned a fish.

See  Sea Creatures and Monsters

Arms of the Worshipful Company of Fishmongers:
Az three dolphins naiant embowed in pale arg finned toothed and crowned or between two pairs of stockfish in saltire arg over the mouth of each fish a crown or on a chief gu three pairs of keys of St Peter in saltire or;
Crest:
Upon a helm on a wreath arg and sa, two cubit arms the dexter vested or cuffed az the sinister vested az cuffed or the hands arg holding an Imperial Crown ppr;
Mantling:
On the dexter side gu doubled or and on the sinister side az doubled arg;  
Supporters:
On the dexter side a merman armed and holding in his right hand a falchion and with his left sustaining the helm and timbre, and on the sinister side a mermaid holding in her left hand a mirror and supporting the arms with her right hand, all ppr;
Motto:
All Worship Be To God Only