Observations on 



the Effects of 



Gas Embolism 



in Captured Adult Menhaden 



A. Clay 

 A. Barker 

 S. Testaverde 

 R. Marcello 

 G. C. McLeod 



ABSTRACT 



The problems of entrapped fish in effluent water of power plants 

 prompted a study of the parameters that induce gas embolism in 

 adult menhaden. Adult menhaden were captured by purse seining 

 in early summer on route to the warmer headwaters of Boston 

 Harbor and maintained in tanks at the New England Aquarium. 

 Supersaturation of the waters in experimental tanks was de- 

 liberately induced and the behavior and certain histological 

 indices studied at a range of temperature, salinity, and super- 

 saturation. 



The occasion of menhaden mortality in the effluent 

 of the Pilgrim Nuclear Power Plant in Plymouth, 

 Massachusetts (Marcello and Fairbanks, 1974), 

 prompted an investigation of the cause, and a 

 search for practical solutions to avoid future de- 

 struction of adult menhaden. If, indeed, supersatura- 

 tion of gases in the discharge canal of power plants 

 induces gas embolism in fish, a number of engineer- 

 ing solutions are possible. An initial step in develop- 

 ing such solutions is to rigorously define the range 

 of environmental conditions that induce gas bubble 

 disease in a menhaden population. 



Unfortunately, investigations of the environ- 

 mental conditions that induce gas embolism have 

 been hampered by an inability to hold adult men- 

 haden in captivity. This may seem strange in view 

 of the numbers of Atlantic menhaden caught and 

 processed each year, but realistic in view of the 

 fact that menhaden are considered a trash fishery 

 whose main use is for fertilizer and cat food. Thus, 

 there has not been any emphasis or effort to main- 

 tain or stock menhaden as a potential sports fishery, 

 nor even to hold adult menhaden for display or 

 research purposes. Consequently, a reliable capture 

 and maintenance program had to be developed. A 

 project was undertaken that incorporated three 

 phases: to capture and maintain a stock of men- 

 haden for testing purposes; to determine lethal 

 levels of supersaturation at various temperatures; 

 and to identify pathological symptoms at these 

 saturation levels. 



The Atlantic menhaden, Brevoortia tyrannus, 

 is a pelagic, euryhaline species. It ranges along the 

 entire eastern United States coastline from Maine 

 to Florida. The general migration pattern includes a 

 northward migration in the spring and summer 

 months from the southern waters. In the early fall, 

 the schools begin to move from the northern areas 

 to the southern portions of the coast. Tremendous 

 schools appear off North Carolina in November and 

 December, where they remain until late spring 

 (Nicholson and Higham, 1966). 



CAPTURE AND MAINTENANCE 



Adult Atlantic menhaden were captured by 

 commercial purse seiners in Boston Harbor during 

 July 1974. Since menhaden are an easily excitable 

 fish and once entrapped may become extensively 

 damaged by contact with the seine, observations 

 were made aboard a carrier vessel to determine the 

 best means of collection. 



The purse seine set consists of a carrier vessel 

 and a purse boat. A spotter plane locates the school 

 and directs the purse boat in setting the net. When 

 the school is encircled, lead weights are released to 

 close the net and trap the fish. The net is hauled 

 aboard the purse boat with the aid of a hydraulic 

 power block until the school is concentrated into 

 the heavily constructed pocket of the seine, called 

 the bunt. Then the carrier vessel comes alongside 

 the bunt, the fish are further "dried up," and 

 brailed into the fish hold of the carrier vessel. 



From our observations, it was determined that 

 the best time to transfer the menhaden was as soon 

 as the carrier vessel was secured adjacent to the 

 bunt. The fish were then transferred from the bunt 

 with a dip net into an aerated, 2.4-m diameter tank 



Clay, Barker, Testaverde: New England Aquarium Corporation, 

 Boston, Massachusetts; with Marcello and McLeod: Boston 

 Edison Company, Boston, Massachusetts. 



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