DIGESTIVE SYSTEM AND FEEDING HABITS OF THE GUNNER, 

 TAUTOGOLABRUS ADSPERSUS, A STOMACHLESS FISH''^ 



Labbish Xing Chao^ 



ABSTRACT 



The cunner, TaiiioiioUihius adspersiis, completely lacks a morphologically or physiologically 

 distinct stomach. The alimentary tract consists of the pharynx followed by a short 

 esophagus with an esophageal-intestinal valve at the junction of esophagus and intestine. 

 The intestine has three limbs and an S-loop. The intestinal bulb where the bile duct enters 

 is present at the anterior end of the first limb. The border between the posterior end of 

 S-loop and the rectum is marked by the intestinal-rectal valve. Histological and histo- 

 chemical observations indicate that the rodlet cells, wandering cells, longitudinal muscle 

 layers, and the rectal valve differ in minor ways from those of other stomachless fishes. 

 Different forms of rodlet cells are found in the bile duct. An alkaline condition (pH 

 values between 7.0 and 8.5) prevails throughout the alimentary tract. Alkaline phosphatase 

 reaction was demonstrated only when food was present in the gut. Cunner are carnivorous, 

 and the feeding habits change with growth. Juveniles feed mainly on planktonic Crustacea 

 and adults on sessile animals (mussels and barnacles). The time between ingestion and 

 defecation of mussels (Mytilidae) by cunner is 10 to 14 hr. Intact mussels can pass through 

 the alimentary tract of the fish undamaged and alive. 



The most abundant lab rid of the New England 

 region, the cunner, TautogoIabrt(s adspersus 

 (Walbaum), lacks a stomach. The absence of a 

 stomach is here defined as the lack of an expan- 

 sion of the alimentary tract between the end 

 of the esophagus and the entrance of the bile 

 duct into the intestine (Figure 1). The mucosa 

 of this region lacks gastric epithelium and gas- 

 tric glands. The alimentary tract is alkaline 

 and lacks peptic digestion. Lack of a stomach 

 appears to be a phylogenetic characteristic of 

 the family rather than an adaptive one associ- 

 ated with feeding in this particular species. 

 The absence of a morphological stomach in 

 teleostean fishes has been recorded in various 

 species of several families, i.e., Atherinidae, 

 Blenniidae, Callionymidae, Cobitidae, Cyprini- 

 dae, Cyprinodontidae, Gobiesocidae, Gobiidae, 



' Contribution No. 19. Marine Science Institute, North- 

 eastern University, Nahant, MA 01908. 



- A portion of a thesis submitted to the Department 

 of Biology. Northeastern University. Boston. Mass., in 

 partial fulfillment of the requirements for the degree of 

 Master of Science in Biology. January 1972. 



■'Virginia Institute of Marine Science, Gloucester 

 Point, VA 23062. (VIMS Contribution No. 539.) 



Manuscript accepted September 1972. 

 FISHERY BULLETIN: VOL. 71, NO. 



2 Cm 



Figure I. — Lateral view of the alimentary tract 

 280-mm SL cunner. E, esophagus; g, gallbladder; 

 III, sections of intestine; S, S-loop of intestine; L, 

 R, rectum. 



of a 

 I, II. 



liver; 



1973. 



Labridae, Mugilidae, Poeciliidae, Scaridae, and 

 Syngnathidae. These families have different 

 feeding habits as noted by Ishida (1936), 

 Harrington (1942). Suyehiro (1942). and Al- 

 Hussaini (1947b) and are not closely related 

 phylogenetically. Al-Hussaini (1949a) also re- 

 corded different feeding habits among three 

 stomachless species of the family Cyprinidae: 

 Ci/prinHs carpio, Ri(tili(K n(tili(,s, and Gobio 

 (j(il>i(r, they are herbivorous, omnivorous, and 

 carnivorous, respectively. Physiological lack of 

 stomach has been noted in various fishes: 

 Fidululus lieteroclitK.s bv Babkin and Bowie 



565 



