Biesiot et al.: Ovarian development in Rachycentron canadum 



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PATTERNS OF SEASONAL MIGRATIONS 

 presumed winter grounds 

 spring migration (to spawning grounds) 

 fall migration (to winter grounds) 



Figure 1 



Patterns of seasonal migration of cobia, Rachycentron canadum, in the 

 eastern Gulf of Mexico and U.S. Atlantic waters. Cobia are found west of 

 the Mississippi River delta but little is known of their migratory pat- 

 terns there (see Footnote 1 in text). Lines and arrows indicate presumed 

 patterns of migration, not specific migratory routes. 



mature females releasing eggs at least once but pos- 

 sibly twice or more during the breeding season; the 

 population experiences a spawning peak during late 

 spring or early summer. Fertilized cobia eggs are pe- 

 lagic and egg diameter is between 1.16 and 1.42 mm 

 (Joseph et al., 1964). 



Although histological changes during development 

 of cobia ovaries have been described previously, 2 

 nothing is known about biochemical changes in the 

 ovary that occur during gonadal maturation. Data 

 on the patterns of change in protein, lipid, and car- 

 bohydrate during oocyte development, and on the 

 subsequent utilization of these reserves by the em- 

 bryos and larvae are important to understanding the 

 early life history of cobia. There is, in fact, very little 

 information about interactions among these three 

 nutrient reserves relative to reproduction despite 

 intensive work on the nutritional requirements of a 

 wide range of fish species. 



Few studies have considered the relationship of 

 the major biochemical components (protein, lipid, 

 carbohydrate, and ash) throughout the course offish 



ovarian development. Dawson and Grimm (1980) 

 showed that protein was higher and more constant 

 than lipid during gonadal development of plaice, 

 Pleuronectes platessa; ash was low and carbohydrate 

 was not measured. Other authors have studied only 

 the ripe (prespawning) stage of fish ovaries. Ripe 

 mullet, Mugil cephalus (Lu et al., 1979), and Atlan- 

 tic cod, Gadus morhua (Kjesbu et al. 1991), ovaries 

 also had higher protein than lipid levels and had low 

 ash and carbohydrate. On the other hand, lipid was 

 the major component of ripe anabantid Trichogaster 

 pectoralis ovaries (Hails, 1983). 



The present study addresses changes in biochemi- 

 cal composition of the cobia ovary throughout the 

 course of gonadal development. Total protein, lipid, 

 carbohydrate, and ash were measured and compared 

 among fish sampled on their spawning grounds in 

 the northern Gulf of Mexico; the different stages of 

 gonadal development were confirmed histologically. 

 In addition, gonosomatic indices (GSI) were calcu- 

 lated on the basis of ovarian developmental stage 

 and month of capture. 



