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



Figure 3.— Ovarian tissue from an age 4 bluefin tuna (119 cm, 33.6 kg) collected off the Middle Atlantic 

 Bight during June 1977. Stage 2 oocytes are present, as indicated by arrow. 



although a few stage 1 oocytes were also 

 observed. Also, in 44% of these fish some stage 



3 oocytes were present, many undergoing 

 absorption. One individual also had some stage 



4 oocytes present. These oocytes were in the 

 process of degeneration. Mostly stage 2 oocytes 

 were present in age 5 fish collected during July 

 (N= 2). Both of these fish also had some stage 3 

 oocytes present, which were undergoing 

 absorption. Stage 2 oocytes were present in all 

 fish collected during August (N = 4). Only one 

 of these fish had stage 3 oocytes present. These 

 stage 3 oocytes were also undergoing absorp- 

 tion. 



Age 6 — The majority of oocytes observed in age 6 

 bluefin tuna collected during June (N = 12) 

 were in stage 2 of development and only a few 

 stage 1 oocytes were observed. Many of these 

 fish (83%) had some stage 3 oocytes present, 

 most undergoing the process of degeneration 

 (Fig. 4). One individual had some stage 4 

 oocytes present, which were also degenerat- 

 ing. Only stage 2 oocytes were found in an age 6 



bluefin tuna collected during August. 

 Age 7 — Mostly stage 2 oocytes were found in age 

 7 fish collected during June (N - 15). Also, 

 some stage 1 oocytes were present in most of 

 these fish and 47% had stage 3 oocytes present, 

 many of which were undergoing absorption. 

 Only stage 2 oocytes were found in an age 7 fish 

 collected during July and another age 7 fish 

 taken during October. 



Some gonadal development, therefore, occurs 

 in these medium female bluefin tuna. However, 

 the simulation of gonadal maturation by young 

 fish that probably do not spawn has been re- 

 ported for king mackerel, Scomberomorus 

 cavalle, (Beaumariage 1973) and Atlantic sail- 

 fish, Istiophorus platypterus, (Jolley 1977). These 

 authors based their determination on the size of 

 the stage 4 oocytes, on their compactness within 

 the lamellae, and on the appearance of many de- 

 generating oocytes. My observations of medium 

 bluefin tuna seem to correspond with the 

 findings of the above authors, although the most 



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