414 



Fishery Bulletin 102(3) 



Figure 6 



Electron micrographs of spermatocytes I (A), spermatocytes II (B), early spermatids (C), mid 

 spermatids (D), late spermatids (E), and spermatozoon (F) from bluefin tuna {Thunnus thynnus). 

 Arrows = synaptonemal complexes; arrowheads = cytoplasmic bridges between spermatids; ax = 

 axoneme; c = centriole; cc = cytoplasmic canal; d = diplosome; dc = distal centriole; f = flagellum; 

 Gc = Golgi complex; m = mitochondria; N = nucleus; pc = proximal centriole. 



of the samples examined in the present study correspond 

 to the mid- and late-maturation stages proposed by Grier 

 and Taylor (1998), and Taylor et al. (1998). Testes at 

 these stages become storage organs that are filled with 

 sperm. The present study encompasses only a short 

 period of the reproductive cycle, which comprises final 

 gonad maturation. However, descriptions of the testicu- 

 lar histology throughout the annual cycle (Santamaria 



et al., 2003) appear to indicate that different maturation 

 classes might be defined in the bluefin tuna based on 

 histological examination of the germinal epithelium (see 

 Taylor et al, 1998; Brown-Peterson et al., 2002). 



Final sexual maturation involves a considerable in- 

 crease in testis size, but no apparent remarkable histo- 

 logical changes, with the exception of a slightly higher 

 frequency of the most advanced stages of spermatogen- 



