412 



Fishery Bulletin 102(3) 



sgA 



sd2 



sgA 



B^'-V- ^ 



4/r 



Se 



(.. 





A 



! ."»" , 



■■■':'.'^' 



m 



/*-■» 



• 



I 



sd3 





mc 



sgA ^ 



// 



'I 



cf 

 Se 



2 urn 



Figure 5 



Electron micrographs of testicular tissue from bluefin tuna (Thunnus thynnus). i A and Bl over- 

 views displaying several spermatocyst types, including single primary spermatogonia (sgA). 

 and clusters of spermatogonia B IsgB), primary spermatocytes iscl I, mid spermatids ( sd2 1. late 

 spermatids (sd.3), and spermatozoa (sz). The germ cells are surrounded by Sertoli cells (Se). 

 Arrowheads = perinuclear bodies ("image"); N = nucleus; n = nucleolus; cf = collagen fibers; 

 mc = myoid cell. 



infrastructure 



Primary spermatogonia are large, ovoid cells (8.55 ±1.07 

 jim) whose nucleus (>5 Jim in its largest diameter) shows 



diffuse chromatin and a single central nucleolus. The 

 cytoplasm contains free ribosomes, a few mitochondria, 

 endoplasmic reticulum cisternae, and several masses 



