Histo-cytopathological study of fish gill upon chronic exposure to harmful algal bloom (HAB)

Abstract

Fish gill is the major organ responsible for respiratory gas exchange, osmoregulation, acid-base regulation and ammonia excretion. Severe gill damage upon exposure to high concentrations of HAB was often associated with high fish mortality. The present investigation studied the sublethal effects of the toxic alga Chattonella marina on gill damage in the fish Epinephelus areolatus and Lutjanus argentimaculatus using light microscopy, scanning electron microscopy and transmission electron microscopy. Fish were exposed to two concentrations of C. marina at 100 cells/mL and 1000 cells/mL for 8 h, and 1, 2, 7 days. Control fish were exposed to the non-toxic strain of Dunaliella spp., and seawater only. Quantitative measurements will be made on changes in size, volume and density of gill epithelial cells (i.e. chloride cells, pavement cells, mucus cells, pillar cells and accessory cells) and cytoplasmic organelles (e.g. secretory vesicles, lysosomes, residual bodies, mitochondria and ER). The threshold levels of toxic dinoflagellate causing significant gill damage will be determined. Quantitative cytological data will be related to the levels of reactive oxygen species (ROS) as well as ATPase activities in gill. The results of this study provide useful information to assess the ecological risk and impact on fish culture upon exposure to low levels of toxic algae.