approximately 30 to 40 cm in total length and about 

 500 g in weight. 



Menhaden from the discharge effluent dis- 

 played two apparent external lesions, i.e., hemor- 

 rhage and subcutaneous emphysema. Subcutaneous 

 emphysema were evident between the fin rays of 

 all body fins especially the dorsal and pectorals 

 (Fig. 2) and within the oral cavity. Subcutaneous 

 ecchymoses (0.5 to 2 cm in size) were evident in 

 various body locations but particularly frequent 

 about the head. In addition, some evidence of pro- 

 nounced exophthalmos was also observed. Fre- 

 quently menhaden in the thermal effluent were ob- 

 served jumping clear of the water and propelling 

 themselves rapidly along the water surface on their 

 sides. Just prior to death, the fish became dis- 

 oriented and gyrated below or on the water surface. 

 On the basis of the external symptoms displayed 

 and the aberrant behavior observed, gas bubble 

 disease was diagnosed as the cause of the menhaden 

 mortalities. At least 90% of the menhaden in the dis- 

 charge channel and thermal plume displayed 

 external symptoms of gas bubble disease. 



On April 11, 1973, several moribund menhaden 

 were transported to the University of Rhode Island, 

 Sea Grant Marine Pathology Laboratory for confir- 

 mation of the gas bubble disease diagnosis and to 

 ensure that no other infectious disease processes 

 were involved in the menhaden mortality. Cultures 

 of kidney, liver, and skin lesions from moribund 



and recently dead menhaden were made in Zobells 

 Marine Broth and cultured at room temperature; no 

 growth was observed after 48 hr. Sections of gill, 

 heart, liver, spleen, kidney, pancreas, stomach and 

 intestine were made and were within normal ranges. 

 Decalcified cross sections of the cephalic area were 

 examined for olfactory and lateral line changes and 

 no significant lesions were noted. Sections of the 

 brain and meninges revealed congestion and foci of 

 hemorrhage compatible with vascular damage. 

 Blood cells were also found free within the ven- 

 tricles. Based on these findings, Wolke (1973) con- 

 curred with the gas bubble disease diagnosis and 

 concluded that the menhaden died from gas emboli 

 resulting in cerebral anoxia and hemorrhage. 



An attempt was made to obtain measurements 

 of dissolved oxygen and nitrogen of Pilgrim Station 

 intake and discharge water by gas chromatography. 

 Dissolved gas levels in replicate samples varied 

 substantially, however. In addition, comparison of 

 dissolved oxygen measurements determined by gas 

 chromatography with those determined by Winkler 

 titration (which showed good agreement between 

 replicate samples) revealed such large discrepancies 

 that the validity of analyses by gas chromatography 

 in this instance are questionable and are not 

 presented. 



Dissolved oxygen concentrations of intake and 

 discharge waters were measured throughout the 

 period menhaden mortality was occurring. Sampling 



FIC. 2 Subcutaneous emphysema between rays of dorsal fin of adult menhaden (photo courtesy 

 of R. E. Wolke, University of Rhode Island, Kingston, Rhode Island). 



Menhaden Mortality at a Power Plant 77 



