In the past it has been believed that these fishes do not feed at 

 the bottom nor along cliffs, but yellowfin taken in the vicinity of the 

 small islands in the eastern part of the Celebes Sea were sometimes found 

 to have gravel in their stomachs. In such cases the food contains a good 

 deal of crustaceans and small mollusks from which it appears that at some 

 places these fishes hunt food along the bottom of the sea„ No such 

 phenomenon has as yet been observed in the case of the spearfishes„ 

 Considering the form of the jaws, this is very natural for it would 

 probably be impossible for a marlin, with the tv/o halves of its beak of 

 such markedly unequal length, to hunt food on thebottom, 



7!hen we come to the large tunas and spearfishes, we find that they 

 can easily swallow whole a skipjack of 10 pounds weight. From the posi- 

 tion of such items in the stomach it appears that the prey is more often 

 swallowed head first than tail first. 



If we look at the fish which come out of tuna and spear fish stomachs, 

 almost all of them have v/ounds on the body just posterior to the head. 

 This may show that when the fish are feeding they first bite their prey 

 from the side and kill it after which they swallow it. The fishes which 

 are ingested into the stomach appear to be digested very rapidly, and only 

 viscous liquid is found in the intestines, no solid matter being discoverable. 

 An interesting thing is 7/hat happens to the skeletons of the fish which 

 are swallowed. Cases are often encountered in which the flesh is completely 

 digested and only a large quantity of bones remains in the stomachs. 

 Since, as already mentioned, no solid matter can be found in the intes- 

 tines, the skeletons must either dissolve completely in the stomachs or 

 else they must be regurgitated. It is not yet known which actually occurs„ 



V. Reproduction 



Almost nothing is known concerning the reproduction of these fishes. 

 It is certain that they spawn in the open sea, that the eg^-s which they 

 lay are very small, and that they are of the so-called pelagic type, which 

 float on the surface of the sea. Since the eggs are extraordinarily small 

 they hatch out in a short time; the parent fish make no particular effort 

 to protect them. Newly-hatched larvae around 2 or 3 mm in length are 

 already living as independent organisms. Ffliat follows is a brief account 

 of what is known at present on this subject. 



Areas which are known with some certainty to be spawning grounds of 

 black tuna are the northeastern portion of the South China Sea, the 

 Pacific coastal waters off northeastern Luzon, and the Bashi Strait. Of 

 course this is not to say that these are the only spawning areaSj, and it 

 is certain that there are other as yet unknown spawning grounds. As was 

 explained in the section on distribution and migrations, the tuna appear 

 in this area from the middle of March to early in June and spawning seems 

 to occur chiefly in May. The catch in the early part of June includes many 

 spent fish. 



The author has previously obtained and reported ripe ovaries of this 

 species. The eg^s are extremely small, the diameter being 0,85 mm. The 



37 



