goldfish and trout exposed to extremely low concentrations of dissolved 

 oxygen for periods of 4 to 25 days (Phyllips, 1947; Prosser, et al., 1957; 

 Ostroumova, 1964] . 



If sublethal concentrations of suspended solids reduce the oxygen 

 available at the gill, then it must be determined if suspended solids can 

 affect gas transport across the respiratory epithelium, inducing a de fac-to 

 hypoxia. Section 111 presents histological evidence that, in white perch, 

 the primary site of respiratory gas exchange, the secondary lamellae, was 

 damaged by exposure to 0.65 g 1"^ fuller's earth. It appears that exposure 

 to sublethal concentrations of fuller's earth can reduce a fish's ability 

 to obtain oxygen by disrupting the gill surface and rendering the tissue 

 partially dysfunctional. 



III. EFFECTS OF SUBLETHAL CONCENTRATIONS OF FULLER'S EARTH 

 ON WHITE PERCH GILL TISSUE 



1. Introduction . 



The gills are the primary site of respiratory gas exchange in most 

 fish. The fish's blood is brought in close contact with the surrounding 

 water at the gill surface. A membrane composed of two layers of cells 

 separates the blood from the water; the gas exchange occurs through this 

 membrane. Oxygen is absorbed from the water by the hemoglobin of the red 

 blood cells, while carbon dioxide and other excretory products, such as 

 ammonia, are released into the water. This system provides little barrier 

 to gas transfer, but leaves the gill vulnerable to toxic or abrasive 

 materials. 



This section presents the results of a histological study of gill 

 tissue in white perch exposed for 5 days to fuller's earth suspensions. 

 The study was designed to determine the damaging effects, if any, of sus- 

 pended mineral solids on the gills of white perch. 



2. Methods . 



White perch were exposed for 5 days to concentrations of 0.65 g 1"-^ 

 fuller's earth. After exposure the fish were removed from the experimental 

 and control tanks and killed. The first gill arch on the right side was 

 removed from each fish and fixed in Bouin's solution. The tissue was 

 embedded in paraffin, and 6-micrometer-thick serial sections were cut. 

 The sectioning plane was dorsoventral, moving serially from the distal to 

 the proximal end of the gill filaments. This made the mucus goblet cells 

 located on the margins of the gill filaments visible; individual secondary 

 lamellae were also clearly visible. Slides containing six to eight serial 

 sections were stained alternately with iron-hematoxylin and Gomori's tri- 

 chrome technique. 



3. Results and Interpretation . 



Gill sections from control fish showed the typical structure for teleost 

 fish (Figs. 1 and 2). Control fish had moderate concentrations of mucus 

 goblet cells, particularly on the anterior margin of each gill filament 

 (Fig. 2). There were concentrations of one to several mucus cells in each 



