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FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



stage residual eggs have the same occurrence 

 pattern as maturing and ripe ovaries. This is 

 true for all the months except January, which is 

 represented by an inadequate sample. The occur- 

 rence of these early-stage residual eggs indicates 

 that spawning actually is a year-round occurrence. 

 Spawning in other equatorial areas of the Pacific 

 likewise seems to be protracted. Schaefer and 

 Marr (1948) found indications of a prolonged 

 spawning season off Costa Rica. Wade (1950) 

 found that the spawning period of yellowfin in 

 the Philippine Islands extended over a considerable 

 period, but that it was most intense during May, 

 June, July, and August. It is probable that the 



of these stages are based on gross microscopic 

 examination and are intended to aid future workers 

 in recognizing these structures. 



Immediately after spawning, these residual eggs 

 (fig. 3) generally resemble the ripe eggs, except that 

 they become shrivelled owing to shrinking of the 

 yolk mass and the resulting collapse of the chorion. 

 The oil sac is usually ruptured, and the released oil 

 appears as bright yellow droplets. The eggs at 

 this stage are still loose and translucent. 



Subsequently the eggs lose their translucence 

 and collect in masses of semiopaque tubules. The 

 eggs are not within the tubule but are entangled 

 in the manv disordered convolutions of the tubule. 



Figure 3. — Individual residual eggs; O., oil droplet; O. S., oil sac. 



prolonged spawning season is accompanied by 

 multiple spawning — in other words, there is more 

 than one spawning per fish in a spawning season. 

 June (1953) considered this to be true for yellowfin 

 in Hawaiian waters, after studying the progression 

 of modal groups in egg-diameter frequencies. 



DESCRIPTION OF STAGES IN RESORP- 

 TION OF RESIDUAL EGGS 



In the beginning of this study, several structures 

 found in the ovaries could not be readily identified. 

 As more ovaries were examined, it became evident 

 that these structures were the remains of ripe eggs 

 from a previous spawning which were in different 

 stages of resorption. The following descriptions 



F.IGURE 4. — Piece of tubule teased from ovary with 

 residual eggs; i. t., inner tubule; o. t., outer tubule. 



