Preliminary observations on the acute inflammatory reaction in the Pacific oyster, Crassostrea gigas (Thunberg)

Abstract

The present study was initiated to study the acute inflammatory process in the oyster, Crassostrea gigas (Thunberg), elicited by injection of turpentine into the tissues. Gross examination revealed a small greenish-yellow area of pus present in all oysters 40 hours after the injection. Histologically, the various pathological changes observable after the injection of turpentine were edema, a general leucocytic infiltration of the tissues, and congestion of the small blood channels after 8 hours. By 16 hours there was a marked vascular dilatation with pavementing of the larger vessel walls by leucocytes and a cellular exudation and migration of leucocytes toward the source of irritation at 24 hours. A thick wall of leucocytes around the wound was characteristic after 48 hours. The appearance of multinucleate giant cells began at 64 hours, as did the mass migration of leucocytes across the epithelial borders of the digestive system. By 72 hours, the digestive tubule secretory epithelium was reduced to a low cuboidal epithelium. At this time pus was becoming a prominent feature in the injured area. Necrotic changes in the gonadal area associated with edema, heavy leucocytic infiltration, distention of the gonadal ducts, and walls of leucocytes forming around the necrotic gonadal areas were observed 72 hours after injection. A distinct abscess was first observed after 88 hours and abscesses were found in almost all oysters from 88 hours through 216 hours. The consistent characteristics of the abscesses were a central area of liquefaction necrosis, surrounded by an area of necrotic leucocytes, with an area of viable appearing leucocytes around the periphery of the lesion. The abscesses were usually in the digestive tubule area and in most instances appeared well confined, even though they lacked any observable signs of fibrous encapsulation. Some oysters exhibited an ulceration of the stomach or intestinal lining. This phenomenon was not observed before 88 hours after injection, the same time at which abscesses were first noticeable.