Abstract Laboratory feeding trials provided the first evidence that a temperate zone fish can grow on a seaweed diet. When the stichaeid fish Cebidichthys violaceus (Girard) was fed for 12 wk on a pelleted seaweed-only diet representing its natural summer diet (10% protein) and on the food modified to make lower (7%) and higher (19%) protein diets, the fish grew on all three but more rapidly on the two higher protein regimens. Maintenance requirements for food and protein of C. violaceus were strikingly low compared to values reported for other fishes. Gut retention times were significantly shorter for fish on the lower protein diet, yet fish consumed equal amounts of energy on the three diets, suggesting that C. violaceus feeds to meet an energy requirement. Nevertheless, the fish converted food protein to body protein with the same efficiency on all three diets and with equal or greater efficiency than those that have been reported for carnivorous fishes.