

• 



1 



8 



10 11 12 13 14 



Figure 1.— Photograph (A) and line drawing (B) of a gel demonstrating electrophoretic mobilities of muscle-tj-pe glycerol-3-phosphate 

 dehydrogenase alleles of yellowfin and bigeye tuna. Bigeye tuna display an allele with a greater anodal mobility. The gel includes 

 adult bigeye (lanes 1 and 13) and yellowfin (lanes 2 and 14) tuna standards and 7 early juveniles, all identified as yellowfin tuna. 

 Note that three individuals (lanes 4, 9, and 11) did not have sufficient activity to stain. 



According to Matsumoto et al. (1972) and Nishikawa 

 and Rimmer (1987), yellowfin larvae less than about 

 12 mm SL have no black pigment spots in the ven- 

 tral tail region. However, Mori et al. (1971) reported 

 and illustrated that there is black pigmentation on 

 the ventral edges of the tail in laboratory-reared 

 yellowfin larvae at 7.8 mm TL. Twenty-one in- 

 dividuals in the 10 to 12 mm TL size range were elec- 

 trophoretically typed as yellowfin tuna in this study. 

 Six of these early juveniles had black postanal ven- 

 tral pigmentation (characteristic of bigeye tuna), 

 while 15 had no black postanal ventral pigmenta- 

 tion (characteristic of yellowfin tuna). 



Variability in larval and early juvenile pigmenta- 

 tion within species, including large changes in pig- 

 mentation over small size ranges, is found within 



many marine fishes (Powles and Markle 1984). 

 Richards and Pothoff (1974) have suggested that the 

 variability of postanal ventral pigmentation is not 

 consistent with specific differentiation within the T. 

 albacares/T. obesus complex. This study supports 

 their claim. 



Early life history studies are necessary for an 

 understanding of recruitment within each species 

 of tuna. Due to the morphological similarity of 

 yellowfin and bigeye tuna larvae and early juveniles, 

 specific separation has not been possible. This study 

 provides a simple method for identifying yellowfin 

 and bigeye tuna larvae and early juveniles. With this 

 technique and additional material, it may be possi- 

 ble to find a morphological character that will allow 

 rapid identification of these two species. 



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