FISHERY BULLETIN: VOL. 80, NO. 1 



somatic index), along with egg diameter 

 measurements, has been a successfully used 

 criterion for selecting specimens for fecundity 

 studies and for determining the spawning peri- 

 ods for various species of fish (Vladykov 1956; 

 Peterson 1961; Erdman, 1968; Mathur and 

 Ramsey 1974; Baglin 1979). 



On the basis of the GSI and the gross 

 morphology and size of ova from the preserved 

 ovaries, western Atlantic female bluefin tuna 

 may be assigned to one of the following 

 developmental stages: 



I. Immature — Ovaries are thin, hollow tubes; 

 nearly spherical, transparent oocytes 

 range from 0.03 to 0.13 mm in diameter 

 (these eggs were stained with acetocar- 

 mine to facilitate measuring). These 

 oocytes were also present during all other 

 developmental stages, and there was no 

 sign of previous spawning. GSI ranges 

 from 0.1 to 0.3. 

 II. Maturing — Ovaries are flaccid, opaque ova 

 up to about 0.63 mm in diameter. GSI 

 ranges from 0.4 to 1.9. 

 III. Mature — Ovaries are firm and full of eggs, 

 with many yellow-orange ova up to 0.85 



mm in diameter. GSI ranges from 2.0 to 

 5.3. 

 IV. Ripe — None of the fish studied were found 

 to be in this developmental stage. However, 

 a few transparent ripe eggs were found in 

 an individual classified as Stage III. The 

 largest of these eggs was 1.16 mm in 

 diameter with an oil droplet 0.30 mm in 

 diameter. This egg corresponds to Stage V 

 of Rodriguez-Roda (1967). A fish would be 

 classified as being ripe only when a 

 substantial number of eggs of this size are 

 present. 

 V. Spent— Ovaries are flaccid; completely 

 spent fish had a few degenerating eggs up 

 to 0.63 mm in diameter. Fish in this stage 

 taken in the summer and early fall months 

 had ovaries with a large amount of fatty 

 tissue. GSI >0.2 but <2.0. 



Size and reproductive data by estimated age 

 and month are presented in Table 2 for 81 small 

 and medium female bluefin tuna from the 

 Middle Atlantic Bight of the western Atlantic 

 and for 15 small and medium eastern Atlantic 

 female bluefin tuna collected by Rodriguez- 

 Roda (1967) and by Cort et al. (1976). Relatively 



Table 2.— Length, weight, and gonadal data for 81 small and medium female western Atlantic bluefin tuna collected during 1974- 

 77 and for 15 small and medium female eastern Atlantic bluefin collected during 1963 by Rodriguez-Roda (1967) and during 1976 

 by Cortet al, (1976). 



'Round weight estimated using functional regression of Baglin (1980) 



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