NOTES 



OLFACTORY 



ELECTROENCEPHALOGRAPHIC 



RESPONSES OF HOMING COHO SALMON, 



ONCORHYNCHUS KISUTCH. TO WATER 



CONDITIONED BY CONSPECIFICSi 



Experimental determination of the home stream 

 of migrating salmon is an important technique 

 for elucidating possible orienting cues. Re- 

 sponses are observed in the fish that are specific 

 to the home-stream water and weaken with in- 

 creasing dilution. 



Two techniques have been employed with 

 some success: Idler et al. (1961) and Fagerlund 

 et al. (1963) found that homed salmon made 

 consistent unconditioned behavioral responses 

 to the water to which they homed. Hara, Ueda, 

 and Gorbman (1965) could electrophysiologi- 

 cally demonstrate unconditioned reponses of the 

 olfactory bulb to the home stream. Hara (1970) 

 in his review states that "this electric response 

 is specific in the sense that it cannot be evoked 

 by water from spawning sites of other groups of 

 breeding salmon." 



We undertook an investigation of lake-run 

 coho salmon, 0)icorhy)ichi(s kisutch, to deter- 

 mine whether these fish exhibited specific ol- 

 factory bulb responses to home water. We tested 

 salmon from two different home streams, exam- 

 ining responses to waters both on and off the 

 migration routes. Furthermore, our field situa- 

 tion allowed us to assess the effects of the re- 

 turning adult spawners upon the olfactory 

 quality of the home stream. 



Materials and Methods 



The experimental fish were hatched from eggs 

 obtained from a Michigan fish hatchery and 

 raised in a Wisconsin hatchery for 1.5 yr. In 



' This work was completed under financial support from 

 the National Science Foundation (Grant No. GB 7616X) 

 to Prof. A. D. Hasler and the University of Wisconsin Sea 

 Grant Program, which is a part of the National Sea 

 Grant Program maintained by the National Oceanic 

 and Atmospheric Administration of the U.S. Department 

 of Commerce. 



the spring of 1969 approximately 1 mo prior to 

 smolting, they were placed in small impound- 

 ments in tributaries of the Ahnapee River and 

 the Kewaunee River (Kewaunee County, Wis.) 

 to which numerous fish have returned in pre- 

 vious years. After initiation of smolting, they 

 were allowed to leave the ponds and make their 

 way downstream to the rivers and thence to 

 Lake Michigan (Figure 1). In the fall of 1970, 

 the mature fish were trapped in weirs on their 

 return up the respective tributaries. The EEG 

 (electroencephalographic) experiments were 

 conducted within 1 km of the trap at the Ahna- 

 pee site. 



Our experimental procedure was similar to 

 that used by Hara et al. (1965). The fish was 

 paralyzed with gallamine triethiodide (2 mg/ 

 kg), and water was perfused continually over 

 the gills. An electrode was placed near the rear 

 margin of the exposed olfactory bulb. The re- 

 sponses, evoked by perfusion of the ipsilateral 

 naris, were amplified (Bio-electric Insti*uments, 

 model DS2C2) and recorded on a two-channel 

 oscillograph (Hewlett Packard, model 7712B) 

 for later analysis. This oscillograph was equip- 

 ped with an integrating preamplifier for efficient 

 quantification of bulbar activity. Responses re- 

 ported later are expressed as the sum of the 

 positive areas under the response wave. 



Our procedure differed from that of previous 

 workers in two ways: 



1. A monopolar stainless steel microelectrode 

 (Transidyne General, model 415100K) was used 

 instead of a bipolar one. The indifferent elec- 

 trode was clipped to the contralateral operculum. 



2. Instead of direct introduction of stimuli to 

 the naris via a wash bottle, a perfusion appara- 

 tus allowed one of four samples to be inter- 

 spersed between a continuous tap water rinse 

 (1 ml/s). Every 75 s, test water (10 ml) was 

 introduced into the interrupted tap water flow. 

 The median response to each stimulus was then 



- Reference to trade names does not imply endorsement 

 by the National Marine Fisheries Service, NOAA. 



893 



