FISHERY BULLETIN: VOL. 71, NO. 2 



Table 1. — Gut content of 68 cunners, Tuiiiofiolahnis 

 adsper\ii.\. from Nahant, Mass. 



during the active feeding season (May to Sep- 

 tember). The foods were mainly mussels My- 

 tilus edulis and Modiolus modiolus, barnacle 

 Balanus balanoides, tunicate Amaroucium sp., 

 and small specimens of the green sea urchin, 

 Strongylocentrotus drobachieyisis. Entire gut 

 contents may consist entirely of one species 

 mentioned above or, usually, of a mixture of 

 these foods. Also some seaweeds, such as 

 Chondrus, Laminaria, Polysiphoiiia, and Por- 

 phyixi, were often associated with the animal 

 foods. Occasionally, crabs, amphipods, and 

 microcrustaceans (copepods, etc.) were found. 

 In juvenile specimens (less than 40 mm SL), 

 amphipods and microcrustaceans were the 

 main food. The food was well triturated in 

 most cases although entire mussels (less than 

 20 mm shell length) and, in one specimen, a 

 crab leg longer than the first portion (I) of the 

 intestine (Figure 1) was observed. In aquaria, 

 cunners found their food by sight. They may 

 pick up a whole mussel from the bottom or 

 catch falling ones as they are introduced into 

 the tank. Also, they removed small mussels 

 one by one or as batches from clusters. Occa- 

 sionally, the food, as well as mussel shell 

 fragments, was spat out and reswal lowed. 

 Feeding activities greatly decreased during the 

 winter when water temperature in the aquaria 

 dropped below 4°-6°C. This was especially notice- 

 able in the large individuals caught during 

 the previous summer. 



Movement and Digestion of Food 

 Materials within the Gut 



The gut in unfed cunner had little or no 

 fluid in the lumen. The intestine and rectum 

 were rather constricted with thick walls. During 

 feeding, small mussels were picked up with 

 the jaw teeth and triturated by the pharyngeal 

 teeth before entering the esophagus. The crushed 

 mussels were pushed back into the eophagus 

 and intestine due to continuous food ingestion 

 during the feeding period. Feeding continued 

 until the food was packed up to the sigmoid 

 loop (Figure 1) and occasionally even to the 

 rectal valve or rectum. The intestinal lumen 

 distends and the wall in turn becomes thinner 

 when the gut is full. The shells of one feeding 

 period always moved as a unit separate from 

 the next feeding period. A period of 10-14 hr 

 was required for mussel shells from a single 

 feeding period (V2-I hr) to pass through the 

 alimentary tract. The compact mass of shells 

 moving along the intestine sometimes straight- 

 ened the S-loop. Food storage in this stomach- 

 less fish was achieved mainly by the intestine 

 anterior to the S-loop. The loop between sec- 

 tions I and II formed a saclike reservoir 

 (Figure 1). Ingested foods remained in section 

 III longer than in the other loops suggesting 

 that this section may be responsible for more 

 digestion and absorption than the other sec- 

 tions. Fluid developed in the lumen during 

 and for a short while after the presence of 

 shells. The amount of bile secretion depended 

 on the quantity of food ingested. The volumes 

 could not be estimated in the present study. 

 In most fish with a full gut which were dis- 

 sected immediately after capture, the gall- 

 bladders were shrunken or contained brownish 

 fluid. The entire range of pH value found in all 

 parts of the gut, both empty and full, was 

 7.0-8.5, thus suggesting alkaline digestion in 

 the cunner gut. 



DISCUSSION \ 



Digestive System 



The morphology of the mouth and buccal 

 and pharyngeal cavities of the cunner is similar 



580 



