in the stomachs, and little or no accumulation in the intestines (Figs. 

 C-9 and C-10). 



4. Conclusions . 



A mechanism for gill cleansing in white perch, striped bass, and hog- 

 chokers in highly turbid water was entrapment of particulate matter on 

 the gills and transport of entrapped particles through the alimentaryi 

 canal. 



Extremely fine particles, such as resuspended bottom muds, fuller's 

 earth, and Hydrite Flat-D, accumulate more than larger particles (Hydrite 

 MP). 



5. Additional Observations and Discussion . 



Microscopic examination of gills revealed a possible mechanism for 

 through-gut transport of suspended particles. Gills examined at X 30 

 showed that fine particles become entrapped between gill filaments and 

 between the secondary lamellae. Fish exposed to the suspended solids had 

 streams of particle- laden mucus on the gill and attached to the pharyngeal 

 teeth on the inner margin of the gill arch. A function of the pharyngeal 

 teeth is to assist in passing food from the mouth to the esophagus, and it 

 is likely that the mucus streams on the gill and on the pharyngeal teeth 

 were being ingested. However, the hogchoker, a demersal fish, had a 

 reduced accumulation of particulate matter in the gut when exposed to 

 similar concentrations of the solids used with white perch and bass. 



Few of these data may be directly compared because of the wide range 

 of suspended solids concentrations. However, it is evident that accumu- 

 lation of particles was much the same in several instances, regardless of 

 concentration. Finer solids accumulated the most; i.e., fuller's earth 

 (75 percent <2 micrometers, median size 0.5 micrometer), Hydrite Flat-D 

 (40 percent <2 micrometers, median size 4.5 micrometers), and resuspended 

 natural muds (70 percent <2 micrometers, median size 0.87 micrometer). 



Mucus stream transport of particles exposes the entrapped material to 

 normal digestive processes and, thus, to a wide range of chemical environ- 

 ments. Particles are exposed for varying periods of time to acid conditions 

 in the stomach. The pH ranges from 2 to 3 and material undergoes a strong 

 acid hydrolysis. The pH environment changes from acid to moderately basic 

 as material passes from the stomach to the intestine (pH 7 to 8) . Hydrol- 

 ysis of food material in the intestine is carried out by enzymatic processes. 



Particles in the stomach are exposed to approximately the same condi- 

 tions as absorbed materials stripped from particulate matter for chemical 

 analysis. Potentially toxic materials such as heavy metal ions, pesticide 

 residues, petrochemical residues, and various biocides of organic origin, 

 may become available to the organism. Through-gut transport of particles 

 removed from suspension provides an avenue for accumulation of noxious 

 material in the tissue of fish. 



77 



