SPAWNING OF YELLOWFIN TtJNA 



263 



Figure 7. — Part of ovary showing shrunken masses of residual eggs; m., mass of residual eggs. 



functioning of the ovaries. There were seldom 

 more than five worms in a single ovary, and in 

 only one instance did the ovarian tissue seem to 

 be pathological owing to heavy infestation. Fish 

 with infested ovaries were found throughout the 

 central equatorial Pacific. 



SUMMARY 



This study is based on data obtained in the field 

 relative to the time and place of spawning and 

 the size of yollowfin tuna at time of spawning, 

 and on laboratory examination of ovaries of yellow- 

 fin tuna obtained on POFI e.xploratorv-fishing 

 trips made in the central equatorial Pacific from 

 February 1950 to June 1954. Study of the ovaries 

 and of the data on tlie size and distribution of the 

 spawning fish led to the following conclusions: 

 (1) The size at sexual maturity may be as small as 

 70 cm., but usually is greater than 120 cm.; (2) 

 the spawning season extends throughout most of 

 the year, with November, December, and January 

 the months of lowest spawning intensity; (3) the 

 spawning grounds seem to include the entire 

 equatorial Pacific. 



During the course of this investigation, stages 

 in the resorption of residual eggs were observed and 

 described. 



Unidentified nematodes were found in 88 per- 

 cent of a sample of 25 ovaries. In most instances, 

 the nematodes did not seem to be present in 

 sufficient numbers to affect egg production seri- 

 ously. 



LITERATURE CITED 



BiNi, Giorgio. 



1952. Osservazioni suUa fauna marina delle coste del 

 Chile e del Peril con sp<'ciak' riguardo alle specie 

 ittiche in gcnerale ed ai tonni in particolare. BoUet- 

 tino di Pesca, Piscicoltura e Idriobiologia, vol. 7 (n. s.), 

 fasc. 1: 11-60. Roma. 



IwATE Prefecture Fishery Experiment St.^tio.v. 



1953a. South Sea tuna fishing survey. Rept. No. 1. 



1953b. South Sea tuna fishing survey. Rept. No. 2. 

 June, Fred C. 



1953. Spawning of yellowfin tuna in Hawaiian waters. 

 U. S. Department of the Interior, Fish and Wildlife 

 Service, Fishery Bull., No. 77, vol. 54, pp. 47-6-1. 



Marr, John C. 



1948. Observations on the spawning of oceanic skipjack 

 (Katsuwonus pelamis) and yellowfin tuna {Neothunnus 

 macroptent.i) in the northern Marshall Islands. U. S. 

 Department of the Interior, Fish and Wildlife Service, 

 Fishery Bull., No. 44, vol. 51, pp. 201-206. 

 Mead, Giles W. 



1951. Postlarval \eothunnus mricropterux, Auxis (hazard, 

 and Eiithynnus linealus from the Pacific Coast of 

 Central America. U. S. Department of the Interior, 

 Fish and WildUfe Service, Fishery Bull., No. 63, 

 vol. 52, pp. 121-127. 



