BAGLIN, JR.: REPRODUCTIVE BIOLOGY OF WESTERN ATLANTIC BLUEFIN TUNA 

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JUNE 

 N = 91 



JULY 



N = 12 



AUG. 



N-16 



Figure 5.— Mean egg diameter of largest ovarian egg as determined from histological sections from monthly samples (N) of 

 A) female giant bluef in tuna from the Gulf of Mexico and the Florida Straits (March through June 1955, 65-67. 76-78) and from 

 off New England (July through October 1974-75, 77), and B) female bluefin tuna ages 3-7 from off the Middle Atlantic Bight 

 (June through August 1974-77). 



the earliest age at which a majority of females 

 could possibly reach maturity. However, a 

 majority of vitellogenic oocytes in these age 6 fish 

 were being absorbed and most likely would not 

 have been spawned during the years when these 

 fish were taken. As previously noted, I observed 

 no vitellogenic oocytes in age 3 fish, but if Sella 

 (1929) and Rodriguez-Roda (1967) are correct, 

 eastern Atlantic bluefin tuna may reach 

 maturity at an earlier age than their western 

 Atlantic counterparts. 



Vitellogenic oocytes were not found in the two 

 giant bluefin tuna (205 and 207 cm) taken during 

 the March 1966 MV Delaware Cruise 66-2 (lat. 

 37°24'N, long. 67°32'W). Vitellogenic oocytes 

 were found in one of three giant fish ( 190-213 cm) 

 taken during April 1965 on the MV Delaware 

 Cruise 65-3 (lat. 35°54'N, long. 72°51'W). 

 Evidently this area of the western North 

 Atlantic was not an important spawning area for 

 bluefin tuna during March-April. 



Vitellogenic oocytes (stages 3 or 4) were 

 present in all giant bluefin tuna taken from the 

 Gulf of Mexico and Florida Straits during 1955, 

 1967, 1976, 1977, and 1978 during March {N = 

 24), April (N = 61), and May (N= 54) (Figs. 6, 7). 

 In one of two fish taken in June 1967 and 1977, 

 stage 3 and stage 4 oocytes were present; in the 



other fish all the vitellogenic oocytes had been 

 spawned or absorbed. On the average, the larg- 

 est oocytes in all of the fish for July (N - 10), 

 August (N - 10), September (N= 16), and October 

 (N = 12) from off New England during 1974, 

 1975, and 1977 were in stage 2 (Fig. 8). 

 Vitellogenic oocytes were generally absent from 

 these fish. 



I found degeneration and absorption of ad- 

 vanced unovulated eggs more common as the 

 season progressed. This agrees with the findings 

 of Frade and Manacas (1933) for eastern 

 Atlantic bluefin tuna. Distinctive atretic bodies, 

 formed from the remnants of oocytes that were 

 not shed, were present in the female giant 

 bluefin tuna collected during March through 

 October. Topp and Hoff (1971) also reported 

 atretic body formation in the ovaries of a single 

 giant female collected from the west Florida 

 coast during May. As previously described by 

 Smith (1965), these atretic bodies form a 

 characteristic brownish mass, the corpus 

 atreticum, and are made up of amorphous 

 brownish granules, phagocytes, and clear yellow 

 pigment globules (Fig. 9). I found that empty 

 follicles left behind after the ripe oocytes are 

 released degenerate rapidly. This was also 

 observed for eastern Atlantic bluefin tuna by 



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