Figure 4. — Microscopic section of base of ulcer from same black marlin showing ex- 

 tensive fibrosis laminated around old nematodal debris (H & E stain, 25 x). 



DISCUSSION 



Several possible causes of the ulcers may be con- 

 sidered. They are (1) mechanical injury to the 

 stomach lining from sharply pointed food items, (2) 

 parasites, (3) digestive processes due to gastric se- 

 cretions between the time of death and time of exam- 

 ination, and (4) excess gastric secretions. 



The most likely cause is either mechanical injury 

 or parasites, or the effect of both in the same 

 stomach. Blue and black marlins feed heavily on 

 fish, many having sharply pointed projections. Ex- 

 amples are the dorsal spines of skipjack tuna, Kat- 

 suwonus pelamis, and yellowfin tuna, Thunnus al- 

 bacares. Both of these tunas are commonly eaten by 

 marlins. We have recovered a sliver of bonelike ma- 

 terial from beneath the epithelium of the stomach of 

 a marlin captured during a billfish tournament. Other 

 examples are the spiny puffers, Diodontidae, which 

 sometimes occur in marlin stomachs. Spiny puffer 

 remains were found in one of the stomachs contain- 

 ing an ulcer, and it is possible that multiple punctures 

 of the stomach lining could occur after engulfment of 

 such food. Multiple punctures could also be caused 

 by engulfment of prey items with sharp spines during 

 successive feedings. This could explain instances of 



multiple ulcers in some of the marlin stomachs. For 

 example, the black marlin stomach shown in Figure 

 1 had six ulcers wider than 10 mm and over 50 smal- 

 ler ulcers less than 10 mm wide. 



Evans and Wares (1972) reported finding gastric 

 ulcers in 14% of 563 striped marlin, Tetrapturus 

 auda.x, and 22% of 151 sailfish, Istiophorus 

 platypterus, examined in Mexican and southern 

 California waters in 1968. They did not, however, 

 cite the presence of nematodes, either in stomachs 

 with or without ulcers. They also suggest spines of 

 prey species may have caused the ulcers. 



In those ulcers containing nematodes, it is uncer- 

 tain if the ulcers were caused by the nematodes, or if 

 the nematodes took advantage of the ulcer and bur- 

 rowed inward. Other workers have found a high 

 percentage occurrence of nematodes in marlin 

 stomachs without citing the presence of ulcers. Wal- 

 lace and Wallace (1942) found Contracaecum incur- 

 vum in 60 of 86 stomachs of white marlin, T. albidus, 

 captured off Ocean City, Maryland. Morrow (1952) 

 reported finding C. incurvum in each of 53 

 stomachs of striped marlin, M. mitsukurii ( = T. 

 audax), from New Zealand. If this nematode 

 causes ulcers, its association with ulcers should be 

 common, which is not the case, according to pub- 



152 



