M. H. Schiewe 

 D. D. Weber 



Effect of Gas I 



Bubble Disease 



on Lateral Line 



Function in Juvenile Steelhead Trout 



ABSTRACT 



Normal lateral line response of juvenile steelhead trout, Salmo 

 gairdneri, to a standardized set of stimuli was compared with 

 the response of fish affected by gas bubble disease. Electro- 

 physiological monitoring of individual afferent nerve fibers 

 showed that as gas emboli formed in the scale pockets of the 

 trunk lateral line of stressed fish, the ability to respond to 

 stimuli was either diminished or completely disappeared. Fur- 

 ther testing demonstrated that this sensory loss is reversible 

 and that upon return to equilibrated water, accompanied by the 

 disappearance of the gas emboli, normal function was regained. 

 This sublethal effect of gas bubble disease on the lateral line 

 sensory system may be an important element contributing to 

 indirect mortality. 



Mortality of fish resulting from gas bubble disease 

 has been extensively studied and documented (see 

 review by Rucker, 1972). Death results from occlu- 

 sion of major vessels by gas emboli when the total 

 dissolved gas pressure of the water environment 

 (Pn, + P0 2 + ^Ar) exceeds approximately 110% of 

 atmospheric saturation. In addition, some recent 

 studies suggest the possibility of gas bubble disease 

 contributing indirectly to mortality (Couta.nt and 

 Genoway, 1968; Newcomb, 1974; Schiewe, 1974). 



Under close observation, the first visible sign 

 of gas bubble disease in fish is the presence of gas 

 emboli in the continuous scale pockets that form 

 the trunk lateral line. These scale pockets contain 

 the hair cell receptor mechanism of this sensory 

 system. Although controversy still exists concerning 

 the exact function of the lateral line system, it is 

 generally recognized that it responds to near field 

 water displacements (Harris and Van Bergeijk, 

 1962). Behavioral studies (Disler, 1960; Dijkgraaf, 

 1962) tend to support the theory that the lateral 

 line serves as a "distant touch" sensory modality 

 for predator-prey relationships, schooling, and 

 obstacle localization. 



Impairment of a sensory system with such an 

 important role in fish behavior could adversely 

 affect survival. This paper reports electrophysio- 

 logical studies designed to assess the effect of gas 

 bubble disease on lateral line function. 



MATERIALS AND METHODS 



Experimental fish were hatchery-reared juve- 

 nile steelhead trout, Salmo gairdneri, from a 

 uniform population with a mean length and weight 

 of 202 mm and 74 g respectively. All fish were 

 acclimated and tested at a temperature of between 

 13°C and 15°C. The limited temperature range was 

 used because of the dependency of saturation on 

 temperature. 



The fish support system, for monitoring both 

 control and stressed fish, is shown in Fig. 1. Equili- 

 brated water was supplied from a dechlorinated tap 

 water source. Supersaturated water was generated 

 by passing water from the same source through a 

 high pressure pump operated under back pressure. 



FIG. 1 Testing apparatus for monitoring lateral line response 

 of steelhead trout. The black disc adjacent to the glass bulb 

 stimulator is a monitoring hydrophone; and the two electrodes 

 beneath the head of the fish are for volume conduction recording 

 of EKC. 



Schiewe and Weber: 

 Washington. 



National Marine Fisheries Service, Seattle, 



6*9 



