601 



Abstract — This study examined the 

 sexual differentiation and reproduc- 

 tive dynamics of striped mullet iMugil 

 cephalus L.) in the estuaries of South 

 Carolina. A total of 16,464 specimens 

 were captured during the study and his- 

 tological examination of sex and matu- 

 rity was performed on a subsample of 

 3670 fish. Striped mullet were sexually 

 undifferentiated for the first 12 months, 

 began differentiation at 13 months, and 

 were 90% fully differentiated by 15 to 

 19 months of age and 225 mm total 

 length (TL). The defining morphologi- 

 cal characteristics for differentiating 

 males was the elongation of the pro- 

 togonial germ tissue in a corradiating 

 pattern towards the center of the lobe. 

 the development of primary and sec- 

 ondary ducts, and the lack of any rec- 

 ognizable ovarian wall structure. The 

 defining female characteristics were the 

 formation of protogonial germ tissue 

 into spherical germ cell nests, separa- 

 tion of a tissue layer from the outer 

 epithelial layer of the lobe-forming ovar- 

 ian walls, a tissue bud growing from 

 the suspensory tissue that helped form 

 the ovary wall, and the proliferation of 

 oogonia and oocytes. Sexual maturation 

 in male striped mullet first occurred 

 at 1 year and 248 mm TL and 100% 

 maturity occurred at age 2 and 300 

 mm TL. Female striped mullet first 

 matured at 2 years and 291 mm total 

 length and 100% maturity occurred at 

 400 mm TL and age 4. Because of the 

 open ocean spawning behavior of striped 

 mullet, all stages of maturity were 

 observed in males and females except 

 for functionally mature females with 

 hydrated oocytes. The spawning season 

 for striped mullet recruiting to South 

 Carolina estuaries lasts from October 

 to April; the majority of spawning activ- 

 ity, however, occurs from November to 

 January. Ovarian atresia was observed 

 to have four distinct phases. This study 

 presents morphological analysis of 

 reproductive ontogeny in relation to 

 size and age in South Carolina striped 

 mullet. Because of the length of the 

 undifferentiated gonad stage in juve- 

 nile striped mullet, previous studies 

 have proposed the possibility of pro- 

 tandric hermaphrodism in this species. 

 The results of our study indicate that 

 striped mullet are gonochoristic but 

 capable of exhibiting nonfunctional 

 hermaphroditic characteristics in dif- 

 ferentiated mature gonads. 



Manuscript submitted 11 March 2003 

 to the Scientific Editor's Office. 



Manuscript approved for publication 

 31 May 2005 by the Scientific Editor. 



Fish. Bull. 103:601-619 (2005). 



Sexual differentiation and gonad development 

 in striped mullet iMugil cephalus L.) 

 from South Carolina estuaries* 



Christopher J. McDonough 



William A. Roumillat 



Charles A. Wenner 



Marine Resources Research Institute 



South Carolina Department of Natural Resources 



217 Fort Johnson Road 



Charleston, South Carolina 29412 



E-mail address (for C J Mcdonough) mcdonoughcsdnr.scgov 



The striped mullet (Mugil cephalus L.) 

 is distributed circumglobally in tropi- 

 cal and semitropical waters between 

 latitudes 42°N and 42°S (Thomson, 

 1963; Rossi et al., 1998). Even though 

 considered a marine species, striped 

 mullet are euryhaline and can be 

 found year round throughout the full 

 range of estuarine salinities in the 

 southeastern United States (Jacot, 

 1920; Anderson, 1958). Striped mullet 

 are important throughout the world 

 for commercial fisheries and aqua- 

 culture. In the southeastern United 

 States there are large-scale commer- 

 cial fisheries for striped mullet in 

 North Carolina and Florida. South 

 Carolina and Georgia have much more 

 limited landings (NMFS 1 ). 



The commercial effort in the south- 

 eastern United States targets "roe" 

 fish (fish containing roe) during the 

 fall spawning migration. Throughout 

 the rest of the year mullet are fished 

 commercially for human consump- 

 tion (particularly the west coast of 

 Florida) and bait (Anderson, 1958). 

 Striped mullet have a significant eco- 

 nomic impact in the southeast where 

 they represented a landings value of 

 16.4 million dollars from 1994 to 2000 

 (NMFS 1 ). Striped mullet landings in 

 the Gulf of Mexico were significantly 

 higher with a landings value of 86.2 

 million dollars for the same time 

 period. Striped mullet are also one 

 of the most important forage fishes 

 that occur in the estuaries of the 

 southeast and represent a significant 

 food source for upper level piscivores 

 (Wenner et al. 2 ). 



General information on the biol- 

 ogy of striped mullet has been well 

 documented (Jacot, 1920; Anderson. 

 1958; Thomson, 1963, 1966; Chubb 

 et al., 1981) but limited information 

 is available on the reproductive biol- 

 ogy of wild populations (Anderson, 

 1958; Stenger, 1959; Greeley et al., 

 1987; Render et al., 1995). There is a 

 large body of work concerning striped 

 mullet reproduction in aquaculture 

 but many of these studies have con- 

 centrated on females by using arti- 

 ficial manipulation of the reproduc- 

 tive cycle. Although the maturation 

 process of oocytes may be the same 

 as that in wild striped mullet, the 

 environment and conditions under 

 which maturation occurred in these 

 studies was artificial (Shehadeh et 

 al., 1973; Kuo et al., 1974; Pien and 

 Liao, 1975, Kelly, 1990; Tamaru et 

 al., 1994; Kuo, 1995). This lack of in- 



* Contribution 564 of the Marine Re- 

 sources Research Institute, South Caro- 

 lina Dept. of National Resources, Charles- 

 ton, SC 29412. 



1 NMFS (National Marine Fisheries 

 Service). 2001. Unpubl. data. Sta- 

 tistics and Economic Division, 1315 East- 

 West Highway, Silver Spring, Md. 20910. 

 http://www.st.nmfs.gov/stl/index.html. 



2 Wenner, C. A., W. A. Roumillat. J. E. 

 Moran, M. B. Maddox, L. B. Daniel, and 

 J. W. Smith. 1990. Investigations on 

 the life history and population dynamics 

 of marine recreational fishes in South 

 Carolina, part 1, p. 2-22. Completion 

 reports, Project F-37, Charleston, and 

 Project F-31, Brunswick. South Carolina 

 Marine Resources Research Institute, 

 P.O. Box 12559 Charleston, S.C. 29422. 



