Penetration of Spines from a Marine Diatom into the Gill Tissue of Lingcod (Ophiodon elongatus)

Abstract

FISHERMEN from the Porlier Pass area of Vancouver Island were experiencing unusually high mortalities among lingcod (Ophiodon elongatus), which according to common practice were being held in surface live-wells prior to the weekly slaughtering and transport to market. Examination of dead and dying fish showed only that all specimens had discoloured gills with considerable detritus embedded in the gill mucus (Fig. 1). Much of this detritus was composed of Chaetoceros convolutus, one of a common group of marine plankton diatoms¹, and their siliceous spines (Fig. 2). The spines or setæ with their apically directed barbs are shown in Fig. 3. These findings suggested the possibility that the setæ might bring about tissue damage and be a direct or indirect cause of death. Gill tissue is particularly vulnerable to injury from chemical and biotic agents because of its intimate contact with the external environment and because of its delicate structure. It was therefore decided to expose apparently healthy lingcod (18 in.) to 3–4 times the natural concentration (that is, 1–5 × 10⁵ cells/1.) of Chaetoceros while the fish were held in aquaria. Control fish were kept in natural sea water.