VIII « Investigations of the larval ^ non-parasitic phase 

 of the sea lamprey's life cycle 



Methods 



Anmocoetes;; or larvae^ of the sea lamprey are extremely abun- 

 dant in many part.s of the Ocqueoc River watershed and ivere stu- 

 died there in 19h7 and I9U80 They vrere collected by means of an 

 electric shocker and several types of dredges. The shocker "was 

 a portable i, 110-volt, A= Co generator driven by a gasoline engine. 

 This device^ in practice^ passes an alternating current through 

 the "water or bottom betiveen two electrodes. In collecting larval 

 lampreys^ the electrodes were operated at distances of from five 

 to fifteen feet apart^ depending on the locus of operations » The 

 machine liiich I used had a f rxed. maxLmum output of 110 volts and 

 3 amperes. Voltages and amperages within the operating field of 

 the electrodes ivould vary with the nature of the stream bottom 

 and the chemical quality of the water but they would not exceed 

 the maximum output indicated. 



Within the electrical fields many ammocoetes are apparently 

 overcome with convulsive movements which. cause them to emerge 

 from their burrows in the mud and sand„ Some^ emerging either 

 head or tail first into the stream^ are paralyzed and drift davm- 

 stream or lie upon the bottom depending upon the amount of stream 

 current „ Others become paralyzed when half out of their burrows. 

 All of these are easily collected vri. th a scap neto 



Many other ammocoetes are evidently paralyzed as they lie 

 in their burrows o In collecting the larvae^ the electrodes were 

 moved forward very slowly., as a rule., and were often operated 

 continuously in a very limited area for as much as five minutes. 

 Quite frequently an area would appear devoid of lampreys for 

 several minutes. If the position of the electrodes was shifted 

 gently, however, larvae would soon begin to appear^ In spite 

 of intensive collecting efforts in a given area on any day, equiv- 

 alent, or larger^ numbers of ammocoetes could be removed from 

 this same area on several succeeding days. One heavily populated 

 silt bank was "worked over" with the shocker for seven consecu- 

 tive days and collections made on each dayj the largest collection 

 was made on the third day of this series = 



Lamprey larvae recover almost immediately iniien removed from 

 the electrical field by the stream current or by the observer. 

 No prolonged ill effects of subjection to the electrical current 

 are apparent. Nearly all ammocoetes collected tvith an alternat- 

 ing current shocker display some evidence of hemorrhaging in 

 the branchial region. The violent convulsions induced by the 



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