An attempt was then made to find some correlation between the schools or ths 

 season and the degree of maturity as determined by the criteria described above. 

 This Investigation showed no marked change in the degree of maturation either as 

 between schools or as between the different seasons* In all schools at all times 

 from the middle o^ October to December the greatest number of females were of Grade 

 3 maturity, with Grade 2 next, and Grade U least numerous. Among the males those of 

 Grade 3 were most numerous with Grade 2 following. With both males and females fish 

 in Grade 1 were extremely rare^ the only such specimens obseirved being one female 

 of 2.55 kg and two males 2.14 and 3.12 kg taken on October 30 from a school which 

 consisted entirely of small fish. Even from this school a female which weighed 

 2,86 kg and showed Grade U maturity and a male of Grade 3 #iich weighed 2.61 kg 

 were taken. In the latter part of October when I first examined the gonads of 

 skipjack at Palao, I was siorprised to see for the first time these organs in a 

 somewhat advanced state of maturity, ray only previous experience in the matter hav- 

 ing been a few observations made in Shizuoka Prefecture. TShen I went aboard a 

 skipjack boat at that time the captain told me, "Tlie skipjack's eggs get large two 

 times in the year, in November and in May." I waited with great expectations think- 

 ing to myself that if the gonads were so far advanced at this time, I should be able 

 to collect plenty of thoiroxighly ripened ones in November, but my hopes were dashed 

 when November and the December came around and the degree of maturity showed no 

 advance. 



Adding the results described above to the fund of knowledge In this field, I 

 would like to make a few obseirvations. It is generally supposed that the spawning 

 grounds of the skipjack are in wann seas, but when it comes to the point of where 

 and when the skipjack of the tropics spawn we find a variety of opinions held by 

 different individuals.-^ One opinion has it that they spawn all the year round, while 

 others think that there is a spawning season. In the case of these latter, however, 

 even for the waters adjacent to Palao different individuals have differing opinions 

 about when the season is. No conclusions on this point can be dirawn from the in- 

 sults reported in this paper, but since the maturity of the gonads remains at al- 

 most the same level from October to December without any fluctuations during that 

 period it can be supposed that perhaps they remain at about this same stage of 

 development throughout the year. Some points which agree with this hypothesis are: 

 (1) In Japan the top-minnows (jnedaka] have ripe gonads in the spring and summer, bat 

 if they are brought to the tropics they can spawn all year round, ^ Furthermore 

 frogs which in Japan spawn only in the spring can be found with ripe gonads all the 

 year round at Palao, It is thought that temperature causes remarkable changes of 

 various sorts in these physiological factors, (2) Skipjack which have ovaries in a 

 rather advanced state of maturity are found the year round at Borneo and elsewhere, 

 A comparison of the opinions of those who believe that the skipjack at Palao have a 

 definite spawning season makes one wonder whether that season does not extend 

 throughout the year. Assuming this to be time, and judging ty the fact that I was 

 unable to find any immature gonrjds like those which I had obtained in Shizuoka 

 Prefecture, and since it cannot be thotight that the individual fish within a school 

 vary in the degree of their sexual maturity, the fact that from October through 

 December the gonads remained at the same level of ripeness seems to indicate, not 

 that the skipjack remain permanently at Palao but that only schools of fish which 



1" Symposium on the Spawning Grounds of the Skipjack and Tuna," South Sea Science. 



Vol.4, No,l [POFI TranslaUon No. 16]. 

 2The writer has been able to get ova from top-minnows in Japan in December by keeping 



them at 25°C, 



