twilight had fed up to the previous evening 

 twilight, passage through the digestive tract 

 while the animals were quiescent took 8 h or 

 less. 



Examination of the matter ingested showed 

 that 70% of the fish sampled contained 78.4 to 

 100% mussels, by volume, in various stages of 

 digestion (Table 3). Next in abundance were 

 remains of various decapod and cirriped crus- 

 taceans, followed by an assortment of other in- 

 vertebrates and debris (vegetable matter, sand, 

 and gravel), with some of the latter probably 

 being ingested incidentally with the mussels. 

 All but two of the fish examined contained over 

 50% mussels, by volume, indicating that mus- 

 sels are the principal food for this population. 



Observations on the tautog's method of feed- 

 ing on mussels, in both the field and laboratory, 

 revealed that after approaching a clump of 

 mussels, the fish would grasp one or several at 

 a time with the anterior canine teeth and then 

 tear them from the substrate with an intense 

 lateral or shaking movement of the head. In no 

 case, in either the field or laboratory, did the 

 initial ingestion process involve crushing with 



FISHERY BULLETIN: VOL 11. NO. 1 



the canines. After initial ingestion, muscular 

 contractions in the bucco-pharyngeal area were 

 clearly seen, evidentally resulting from the 

 shells being crushed by the pharyngeal teeth. 

 When a clump of mussels attached by byssal 

 threads was too large to be processed by the 

 pharyngeal teeth, the fish would alternately 

 ingest and egest the clump until it was sepa- 

 rated into a smaller crushable size. 



The mussels in the digestive tracts consisted 

 primarily of specimens averaging 11.9 mm in 

 length and estimated to be 1 to 2 yr old (Table 3). 

 There was an obvious selection of young, small 

 mussels by all-sized fish. 



While factors such as ease of crushing and a 

 greater digestive efficiency may be involved in 

 the tautog's preference for small, young mus- 

 sels, we found another possible cause related 

 to the limitations imposed by the dimensions 

 of the pharyngeal area where the mussels are 

 crushed. The mouth can accommodate much 

 larger mussels than the crushing apparatus is 

 able to process. For example in the laboratory 

 on 20 occasions, we saw fish that were starved 

 for more than a day attempting to eat mussels 



Table 3. — Relative fullness and contents of tautog digestive tracts. 



' Fullness index — volume empty tract/volume of tract with contents. 

 - Fish no. 7 (Table 1) captured at end of track. 



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