OOCYTE GROWTH AND DEVELOPMENT IN THE STRIPED MULLET, 



MUGIL CEPHALUS, DURING SEASONAL OVARIAN RECRUDESCENCE: 



RELATIONSHIP TO FECUNDITY AND SIZE AT MATURITY 



Mark S. Greeley, Jr.,' Daniel R. Calder,' and 

 Robin A. Wallace^ 



ABSTRACT 



Oocyte growth and development in the striped mullet, Mugil cephalus, were examined during the period 

 of rapid ovarian recrudescence that precedes spawning in coastal waters of northeast Florida. Based 

 on the de novo appearance of yolk proteins detected by polyacrylamide gel electrophoresis, the oocyte 

 size corresponding to the onset of vitellogenic growth was determined to be 0.18 mm (diameter). Through 

 in vitro studies of oocyte responsiveness to steroid stimulation of meiotic maturation, the minimum 

 prematuration oocyte size was determined to be 0.60 mm; largest prematuration oocytes collected dur- 

 ing the study were 0.72 mm. Females with vitellogenic oocytes were first collected in Matanzas Inlet 

 in late September. Females with prematurational oocytes were first observed in mid-October. Minimum 

 size at sexual maturity for female striped mullet in northeast Florida ranged from 23 to 27 cm SL. 



Oocyte size-frequency profiles led to the development of a staging system for striped mullet ovaries 

 that can be related to simpler measurements of reproductive condition such as the gonadosomatic index 

 and the largest oocyte diameter. According to this system, females with prespawning ovaries first ap- 

 peared in Matanzas Inlet during mid-October, then disappeared from the Inlet in either mid-December 

 (1985-86 season) or mid-January (1984-85 season). Females with ovaries in spawning condition were not 

 observed in the Inlet during the 2 years of this study, supporting the commonly held assumption of off- 

 shore spawning. A few females with postspawn ovaries were collected as early as late November. 



The potential fecundity of the striped mullet in northeast Florida was calculated from the size of 

 the single clutch of developing oocytes, and related to both body weight and standard length. 



The striped mullet, Mugil cephalus, is a euryhaline 

 teleost with a nearly worldwide distribution in 

 marine and estuarine waters. Economically impor- 

 tant as a food and bait fish in many areas, the world 

 commercial catch of mullet from 1979 to 1983 aver- 

 aged nearly 185,000 t (metric tons) per year (FAO 

 1984). During this time, a yearly average of almost 

 14,000 t (nearly 8% of the world catch) were caught 

 in the United States, more than in any other single 

 country. Most were caught in the state of Florida, 

 for an average of almost 12,000 t yearly in 1981 and 

 1982 (National Marine Fisheries Service preliminary 

 data, in Comp and Seaman 1985), equivalent to 87% 

 of the United States and 6% of the worldwide catch. 

 In addition to being the basis of large natural fish- 

 eries, M. cephalus has been reared for aquacultural 

 purposes in brackish and freshwater ponds (Brom- 

 hall 1954; Thomson 1966; Pien and Liao 1975) and 



>Whitney Laboratory, The University of Florida, Route 1 , Box 

 121, St. Augustine, FL 32086. 



^Whitney Laboratory, The University of Florida, Route 1, Box 

 121, St. Augustine, FL 32086, and Department of Anatomy and 

 Cell Biolog}', College of Medicine, University of Florida, 

 Gainesville, FL 32610. [Direct all reprint requests to Robin A. 

 Wallace at the Whitney Laboratory.] 



has been the subject of induced breeding in the 

 laboratory (Kuo et al. 1973, 1974a, b; Kuo 1982). 

 General information on the biology of M. cephalus 

 and related species of mullet can be found in Ander- 

 son (1958), Stenger (1959), and Thomson (1966). 



Striped mullet have one breeding cycle per year 

 lasting from 2 to 5 months depending on the loca- 

 tion (Jacot 1920; Breder 1940; Bromhall 1954; 

 Anderson 1958; Arnold and Thompson 1958; 

 Stenger 1959; Tang 1964; Zhitenev et al. 1974; Pien 

 and Liao 1975; Timoshek and Shilenkova 1975; 

 Finucane et al. 1978; Apekin and Vilenskaya 1979; 

 Azoury and Eckstein 1980; Chubb et al. 1981; Dindo 

 and MacGregor 1981). In coastal waters of the 

 southeast United States, spawning has been 

 reported to occur from October through February 

 as determined from the time of appearance and size 

 of larvae and fry (Anderson 1958; Arnold and 

 Thompson 1958), from the presence of migrating 

 mullet with "developing" ovaries (Breder 1940; 

 Arnold and Thompson 1958; Stenger 1959), and by 

 monthly gonadosomatic index (GSI) changes (Dindo 

 and MacGregor 1981). 



In view of the extensive interest in the mullet, it 



Manuscript accepted February 1987. 

 fishery BULLETIN: VOL. 85, NO. 2, 1987. 



187 



