The marine vibrio ANT-500 is a typical psychrophile. The growth range of the bacterium at 35��� S is from a maximum growth temperature of 13.5 C to a minimum growth temperature of -2.5 C or less with the optimum near 7 C. The bacterium elaborates its chitinase enzymes between the temperatures of 1.5 and 13.5 C. The enzyme system is composed of three separate enzymes, probably two chitinases and one chitobiase. The rate limiting step of the enzyme-substrate reaction appears to follow Mechaelis-Menton kinetics. Chitin is the only substrate that induces chitinase synthesis in ANT-500. Chitinase activity was found in the digestive tracts of all species of fish sampled in Yaquina Bay, Oregon. Direct correlations were noted between gut content and chitinase activity in the gut, gut content and percent chitinoclasts in the gut, and chitinase activity and percent chitinoclasts. Fish with little or no chitinous material in their gut contents showed low or no detectable levels no chitinase activity and a low percentage of chitinoclasts, while fish with predominantly chitinous material in their gut contents showed high chitinase activity and a large percentage of chitinoclasts. Neither hydrostatic pressure up to 1000 atm nor lack of oxygen had a detrimental effect on chitinase activity from the gut of Raja binoculata. Sterile stomach fluid from Enophrys bison had no effect upon the growth rates of a pure chitinoclastic and a mixed culture of bacteria isolated from the gut of Enophrys bison; however, the gut fluid did allow for greater cell yield. N-acetyl-D-glucosamine, the end product of chitin decomposition, exhibited a ttglucose effect when added to culture medium. Both the pure and the mixed culture showed repression of growth in early log phase when grown in N-acetyl-D-glucosamine. The chitinase isolated from the gut of Enophrys bison is bacterial in origin. Tests in which the bacterial flora of the gut of Enophrys bison was eliminated by use of chloramphenicol revealed no detectable chitinase activity and no chitinoclastic bacterial populations. Fish in the absence of the antibiotic showed both significant chitinase activity and predominating chitinoclast populations. Other data strongly indicate that the chitinase in many species of marine fishes may also be bacterial in origin. / Graduation date: 1976