594 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE. 



motion without danger of flushing them from the 

 jar. 



One-third of the eggs hatched on June 17 (13 

 days), and the remainder the following day (14 

 days) . Daily morning water temperatures during 

 this period averaged 60.7° F. (extremes of 57° and 

 65° F.). The source of water used in hatching 

 these eggs was Cascadilla Creek, in which water 

 temperatures are similar to those of Cayuga Inlet. 



At hatching, the anterior portion of the trunk 

 emerges from the chorion. The posterior portion 

 may remain within the egg case for as long as 1 day 

 after the anterior end emerges. The yolk sac, 

 which is located ventrally on the posterior half or 

 two-thirds of the body, is expanded only slightly 

 at its anterior portion, but ends in a globular mass 

 posteriorly. This enlargement of the yolk sac 

 tends to hold the posterior end of the ammocoete's 

 body within the shell. 



Habits of Ammocoetes 



The first 2 days after hatching, the ammocoetes 

 remained rather inactive. At this time they were 

 4 mm. long, still opaque, and of cream or light tan 

 color. The caudal portion of the trunk, which 

 was made up largely of yolk sac at this stage, was 

 curved ventrally and anteriorly to give them a 

 hooked appearance. This hook shape disappeared 

 the third day after hatching, when the ammocoetes 

 had absorbed most of the yolk. They very soon 

 became somewhat translucent witli a light suffu- 

 sion of brown pigment dorsally and dorsolateral^*. 



After the yolk had been absorbed the ammo- 

 coetes became active and burrowed rapidly into 

 the soft bottom. Partially buried specimens ex- 

 hibited a negative phototropism. Newly hatched 

 ammocoetes remain in the nest for several days, 

 but later emerge in search of other niches. In 

 Michigan, Applegate (1950) found that newly 

 hatched ammocoetes left the nest between 18 and 

 22 days after fertilization. In Cayuga Inlet, the 

 newly hatched ammocoetes were located along the 

 stream margins, buried in the fine sand-silt sedi- 

 ment. Possibly they were present in the deeper 

 waters also, but they may have been overlooked 

 because of the difficulty in seeing such small crea- 

 tures in deep water. 



Larger ammocoetes occupy various habitats, 

 but most commonly are found in sand and silt 

 deposits into which they can easily burrow. Por- 

 tions of the stream with medium to strong water 



currents and suitable sediments appear to be most 

 satisfactory. Ammocoetes and transforming lam- 

 preys do not emerge from their burrows unless 

 disturbed or unless radical changes occur in water 

 conditions. 



Observations on ammocoetes held in aquariums 

 revealed their method of burrowing. They pene- 

 trate the bottom sediments by thrusting the head 

 downward perpendicular to the bottom and mak- 

 ing very rapid undulatory motions. As soon as 

 the snout and head enter the bottom they draw the 

 body downward by constant undulation of the 

 head and snout in an S-shaped pattern. After the 

 trunk is approximately two-thirds buried, the 

 swimming motions of the posterior end cease, but 

 the undulations of the anterior end continue to 

 pull the body into the sediment. The ammocoetes 

 begin to turn in a horizontal direction after ap- 

 proximately half the body is buried. They then 

 gradually move toward the surface of the sediment 

 until a second opening to the water has been made. 

 This maneuver forms a U- or crescent-shaped bur- 

 row. The sediment fills in the burrow behind the 

 posterior end of the ammocoete. All the water 

 which provides food and oxygen passes through 

 the remaining entrance. 



Mucus secreted by the ammocoete lines the 

 burrow and holds the particles of the bottom ma- 

 terial in place. This lining prevents the entrance 

 to the burrow from collapsing when the ammo- 

 coete retracts within it. The burrow is believed 

 to be a stable excavation within which the ammo- 

 coete lives until driven from it, or until it is de- 

 stroyed by floods or other forces. Once the ammo- 

 coete leaves the burrow it constructs a new one 

 immediately. The length of the burrow is usually 

 less than twice the occupant's length and com- 

 monly only 1 )'i times its length. When mildly dis- 

 turbed, the ammocoete moves backward, away 

 from the mouth of the burrow. When severely 

 disturbed it leaves the burrow and swims rapidly 

 away to enter the bottom sediment at another 

 location. 



Details of the respiration and feeding processes 

 are not thoroughly known. Expansion and con- 

 traction of the branchial chamber, together with 

 action of the velum, pump a continuous stream of 

 water into the ammocoete's oral chamber and out 

 the gill openings. The oral papillae spread 

 branchlike across the entrance to the oral hood. 

 These papillae constitute an excellent strainer to 



