Compressed air was metered into the intake side 

 of the pump to create the desired saturation level. 

 Supersaturated water was maintained at 118 ± 4% 

 of atmospheric saturation in the test range of 13°C 

 to 15°C. Analysis procedures were the gas chromato- 

 graphic methods of Swinnerton et al. (1962) modi- 

 fied by Ebel (1969). 



Anesthesia was accomplished with tricaine 

 methanesulfonate followed by gallamine tri- 

 ethiodide at the rate of 0.6 mg/10 g body weight. 

 At opercular arrest the fish was moved to the testing 

 apparatus where water (equilibrated or super- 

 saturated) was forced over the gills at the rate of 

 1 C/min. If the heart rate, monitored by volume 

 conduction EKG, fell below normal for a given 

 temperature, the experiment was terminated. 



Water level in the testing apparatus was 

 adjusted to provide an unsubmerged area 2 to 3 cm 

 posterior to the operculum. In this area the lateral 

 line nerve bundle was dissected out and placed over 

 a silver, spoon-shaped indifferent electrode. Phos- 

 phate-buffered saline was used to both bathe the 

 exposed nerve and to fill the depression of the 

 spoon. Individual nerve fibers were then teased out 

 and draped over an uninsulated, electrolytically 

 sharpened, stainless steel hook electrode for 

 recording. 



Initial recording of nerve activity during isola- 

 tion was done with a Tektronix® model 565 dual 

 beam oscilloscope coupled with a loudspeaker. 

 Further study and documentation were accomplished 

 by transfer of the recording to a Tektronix® 

 model 5103N storage oscilloscope with a Polaroid® 

 camera attachment. 



Normal response pattern was based on the 

 ability of the associated receptors to respond to 

 varying degrees of stimulation. Once a fiber was 

 isolated, the corresponding receptor response was 

 measured by application of light touch, surface 

 waves, and pulsed water displacements. The pulsed 

 water displacements were generated by a 1 cm 

 glass bulb attached to the cone of an 8-in. loud- 

 speaker driven by a Waveteck® model 144 HF sweep 

 generator. During testing the bulb was positioned 

 5 mm above the appropriate receptors. 



RESULTS AND DISCUSSION 



Our initial studies indicated that individual 

 afferent lateral line nerve fibers would innervate 

 receptors in 1 to 26 scale pockets to form a sensory 

 unit. The resting or spontaneous activity rate of an 

 isolated fiber was directly dependent on the num- 

 ber of scales comprising that sensory unit (Fig. 2). 

 This fact became a useful criteria in support of our 

 findings. 



Activity from over 150 fibers was recorded in 



20 control fish (maintained on equilibrated water) 

 and 10 stressed fish which were maintained on 

 equilibrated water for a short acclimation period 

 and then shifted to supersaturated water. Signs of 

 gas bubble disease began to appear in the stressed 

 fish within 2 to 6 hr. This protocol enabled us to 

 characterize nerve fibers of fish whose lateral line 

 showed three distinct stages of gas bubble occur- 

 rence: no bubble formation, partial bubble forma- 

 tion, and complete bubble formation. 



None of the control fish maintained in equili- 

 brated water developed gas emboli in lateral line 

 scale pockets. All spontaneously active fibers were 

 responsive to light touch, surface waves, and 

 pulsed water displacements generated by the glass 

 bulb stimulator. Corresponding sensory units were 

 easily located and spontaneous activity correlated 

 with number of scales in the sensory unit. 



The scale pockets of the trunk lateral line of 

 stressed fish would progressively fill with gas 

 emboli until complete occlusion occurred. All fibers 

 isolated and characterized under a state of com- 

 plete occlusion did not respond to any form of 

 stimuli except firm pressure on a limited number 

 of scales. The number of scales reacting to stimula- 

 tion did not correspond to the observed spontaneous 

 activity (Fig. 3). 



4 8 12 10 20 24 



NUMBER Of SCALES IN SENSORY UNIT 



FIG. 2 Spontaneous activity of single lateral line nerve fibers 

 and number of scales innervated. Data derived from fish accli- 

 mated and tested at 13°C to 15°C. Regression line (y = 2.49 + 4.29X 

 N = 21) parameters estimated using reduced major axis tech- 

 niques from Miller and Kohn (1962). 



'Trade names are used to simplify description; no endorsement 

 is implied. 



90 Schiewe, Weber 



