FISHERY BULLETIN: VOL. 74, NO. 2 



occur where chemical stimulation is important 

 but other ecological factors usually prevent the 

 animal from associating with other forms 

 (Davenport 1955). 



Over 30 attempts by L. inquilinus to enter sea 

 scallops were observed in the laboratory. The 

 length of time spent swimming along the mantle 

 of the scallop varied, but some fish were able to 

 enter in less than 3 s. After swimming along the 

 mantle most fish turned, placed the head at the 

 margins of the mantle, and attempted to force 

 their way inside the scallop with sustained 

 swimming strokes of the tail. One individual re- 

 peated this activity 10 times before it gave up. 

 The point of entry along the mantle appeared to 

 be selected randomly. Several fish attempted to 

 enter the incurrent and excurrent opening. The 

 scallop usually did not react to the fishes' en- 

 trance and only occasionally responded by closing 

 the valves slightly. The red hake, Urophycis 

 chuss, enters and exits the scallop only through 

 the excurrent opening (Musick 1969). 



Perhaps there is individual variation in the ac- 

 ceptance of fish by scallops. On two occasions, 

 scallops rejected L. inquilinus after they had en- 

 tered the scallop by clapping the valves together 

 and thus forcing the fish out of the mantle cavity. 

 In each instance, the fish came to rest a few 

 inches from the edge of the scallop. The fish re- 

 mained still as the sand stirred up by the scallop's 

 activity settled over it. Within a few minutes, the 

 fish returned to the scallop and attempted to 

 enter again. 



Once inside the mantle cavity of the scallop, 

 the fish attached by their discs in an inverted 

 position to the mantle tissue of the left valve. 

 Fish have been observed in this position approx- 

 imately 20 times, either by viewing through the 

 excurrent or incurrent opening or picking 

 the scallop out of the water and looking in as it 

 clapped. Often several fish were observed in the 

 same scallop simultaneously. This position in the 

 scallop is the same as that preferred by fish at- 

 tached to clapper shells and other smooth sub- 

 strates. In approximately 100 other instances, L. 

 inquilinus presence in sea scallops was confirmed 

 by their absence elsewhere in the aquaria. 



Liparis inquilinus and U. chuss apparently 

 cooccur in sea scallops frequently and in consid- 

 erable numbers. We have collected these fishes 

 together in sea scallops from Georges Bank in 

 September, November, and December. In the 

 Mid- Atlantic Bight (4 August 1969, lat. 39°40'N, 



long. 73°09'W, 40 m) a 141-mm sea scallop con- 

 tained a red hake (21 mm TL) and 21 L. inquili- 

 nus which averaged 16.5 mm TL. A 125-mm scal- 

 lop yielded two U. chuss (43 and 47 mm TL) and 

 two L. inquilinus (23 and 24 mm TL). Goode 

 (1884) also reportedL. lineatus (= inquilinus) and 

 Phycis (= Urophycis) chuss as companions in sea 

 scallops. These two fishes may not be in direct 

 competition for this particular habitat since the 

 L. inquilinus remain attached to the upper sur- 

 face of the cavity and U. chuss swims in the mid- 

 dle of or rests on the bottom of the cavity (Musick 

 1969). 



Sea scallops apparently suffer no ill effects 

 from the association with L. inquilinus. Of sev- 

 eral thousand host sea scallops opened during 

 this study, none had noticeable internal damage 

 which could have been caused by L. inquilinus. 

 These partners do not compete for food since L. 

 inquilinus feeds principally on larger crustaceans 

 and sea scallops are microplanktonic filter feed- 

 ers (Bourne 1964). 



Diel Rhythm in the Fish — 

 Scallop Association 



Juvenile L. inquilinus exhibit a diel rhythm in 

 their association with sea scallops. In aquaria, 

 fish were outside of the sea scallops and actively 

 swimming during periods of darkness. The color 

 pattern of the fish faded during dark periods but 

 returned within approximately 5 min after the 

 lights were turned on. Fish were usually inside of 

 scallops or attached to some substrate in the 

 aquarium during light periods. When the lights 

 went off on their regular cycle, the fish would 

 often leave the scallops and become active within 

 5-10 min. These reactions to light and dark were 

 immediate even when the dark-light cycle was 

 changed drastically during a single day. Liparis 

 inquilinus which were collected from sea scallops 

 during a 24-h period on 4-5 August 1969 near 

 Hudson Canyon (Figure 6) exhibited the same 

 pattern (Figure 7). During this period, 3,595 L. 

 inquilinus, averaging 21.0 mm TL, were collected 

 from 616 of the 841 scallops examined. In one in- 

 stance, 32 fish were found inside a 139-mm scal- 

 lop. Fish were more abundant in scallops and more 

 scallops contained fish during the day than at 

 night (Table 2). However, some fish were present 

 in scallops during every sampling period. The 

 greatest increase and decrease in the number of 

 fish per scallop occurred around sunrise and sun- 



416 



