McDonough et al.: Sexual differentiation and gonad development in Mugil cephalus 



603 



Aw 



C^ 



4 (*- - ^rr"-^, S ' Helena Sound 



A' frills Bay Cape Remain 



5^ 



^LM Charleston Harbor 



SOUTH CAROLINA 

 Ji_ 



Figure 1 



Map of coastal South Carolina with estuaries where trammel net collections were made: Cape Romain, Charleston 

 Harbor, and Ashepoo River, Combahee River, Edisto River (ACE) Basin, as well as the coastal rivers where elec- 

 troshock collections were made. 



and gonad tissue joined in striped mullet (Chang et 

 al., 1995). Comparisons of oocyte density from different 

 sections of striped mullet ovary have also demonstrated 

 uniform distribution throughout the ovary (Shehedeh et 

 al., 1973; McDonough et al., 2003). A gonadosomatic in- 

 dex (GSI) was calculated for specimens according to the 

 method of Render et al. (1995) where GSI was expressed 

 as a percentage of gonad weight (GW) divided by body 

 weight (BW) minus gonad weight, such that 



GSI = (GW/(BW-GW))x 100. 



Histological processing 



The tissue samples were processed by using standard 

 wax histology techniques (Humason, 1967). Tissues 

 were embedded in paraffin and cut on a rotary micro- 

 tome. The sections, which ranged from 5 to 7 ^m thick, 

 were then placed on microscope slides and stained with 

 standard haematoxylin and eosin-Y staining techniques 

 (Humason, 1967). After staining, tissue sections were 



sealed under a cover slip and evaluated for sex and 

 maturity with a compound light microscope at lOOx 

 magnification. The sex of each specimen was determined 

 to be male, female, or undifferentiated. Maturity was 

 assessed according to a modified version of the sched- 

 ule used by Wenner et al. (1986) that was adapted by 

 the authors to work with isochronal spawning fish, as 

 well as assessed with previous models of reproductive 

 development (Stenger, 1959; Grier, 1981; Wallace and 

 Selman, 1981) (Table 1). Ovarian atresia was divided 

 into four distinct phases as described by Hunter and 

 Macewicz (1985). For the sake of consistency, the same 

 terminology was used to describe the four phases of 

 ovarian atresia in striped mullet in this study: alpha, 

 beta, gamma, and delta (see Table 2). These evaluation 

 methods were based on identification of morphological 

 characteristics evident in histological sections. Speci- 

 mens were evaluated by two readers to avoid bias. Any 

 discrepancies of maturity stage between readers were 

 either mutually resolved or the specimen was excluded 

 from further analysis. 



