SEASONAL CHANGES IN THE OVARIES OF ADULT 

 YELLOWTAIL FLOUNDER, LIMANDA FERRUGINEA 



W. Huntting Howell 1 



ABSTRACT 



Seasonal changes in both macroscopic and microscopic appearance of yellowtail flounder ovaries are de- 

 scribed, as well as seasonal changes in the gonosomatic index. Oocytes pass through seven cytologically dif- 

 ferent developmental stages. By examining seasonal changes in the relative abundance and sizes of these 

 stages, it was found that oogenesis occurs in two broad phases, each lasting about 1 year. The previtellogenic 

 phase begins as a new stock of oogonia arises each year, principally in the summer months following spawn- 

 ing. These rapidly develop into early perinucleolus oocytes, which in turn develop into resting stage oocytes 

 by the fall. Most oocytes remain in this stage until the following spring, when they then develop into late 

 perinucleolus oocytes. The vitellogenic phase begins as these late perinucleolus oocytes, now about 1 year old, 

 become transformed into early maturing oocytes through the accumulation of yolk. This occurs during the 

 late spring and summer months. Through the following fall and winter the cytoplasm completely fills with 

 yolk as oocytes reach the late maturing stage. Shortly before spawning the following spring, the final hyaline 

 stage of development is reached. 



These results indicate that there are two synchronous groups or populations of oocytes present in the ovary 

 at any given time. Members of the vitellogenic group are in their second year of development, and will be 

 released in the upcoming spawning season. These are recruited from a previtellogenic group which 

 developed during the previous year. 



Seasonal changes in the microscopic appearance of the ovaries were well correlated with seasonal changes 

 in both gonosomatic index and macroscopic appearance. 



Yellowtail flounder, Limanda ferruginea, range along 

 the Atlantic coast of North America from the Gulf of 

 St. Lawrence to the Chesapeake Bay (Bigelow and 

 Schroeder 1953). Over much of this range the species 

 supports important commercial fisheries. Despite 

 their economic importance, comparatively little is 

 known of their reproductive biology. Spawning sea- 

 son is latitudinally dependent, with most spawning 

 occurring from April through June in the southern 

 portion of the range, and from May through July in 

 the northern portion (Bigelow and Schroeder 1953; 

 Royce et al. 1959; Pitt 1970; Smith et al. 1975; Able 

 1978; Colton et al. 1979). Females generally mature 

 between 30 and 40 cm TL (total length), which is 

 reached in 2-4 yr in the southern portion of their 

 range (Royce et al. 1959) and in 5-8 yr further north 

 (Scott 1954; Lux and Nichy 1969; Pitt 1970). The 

 fecundity of Grand Bank, Newfoundland, yellowtail 

 flounder has been related to total length and age by 

 Pitt (1971), and Howell and Kesler (1977) related 

 fecundity of southern New England yellowtail floun- 

 der to total length, age, and ovary weight. 



The purpose of this research was to examine 

 seasonal changes in both the macroscopic and mi- 

 croscopic appearance of the ovary, to examine sea- 



'Department of Zoology, University of New Hampshire, Durham, 

 NH 03824. 



Manuscript accepted November 1982. 

 FISHERY BULLETIN: VOL. 81, NO. 2, 1983. 



sonal changes in gonosomatic index (GSI), and to 

 describe histologically the process of oogenesis. 

 Specific questions addressed were: 1) What develop- 

 mental stages does an oocyte pass through from 

 oogonium to fully ripe egg? 2) How long does this pro- 

 cess take, and when do the changes from one stage to 

 the next occur? 3) How do seasonal histological 

 changes relate to seasonal changes in both GSI and 

 the macroscopic appearance of the ovary? These 

 data provide baseline information against which 

 either experimental results or field data can be com- 

 pared, and which are useful in identifying environ- 

 mental variables that may effect eventual fecundity. 



MATERIALS AND METHODS 



Data were collected from commercially landed fish 

 at the Pt. Judith, R.I., Fisherman's Cooperative at 

 approximately monthly intervals from June 1977 

 through November 1978 (Table 1). On each sampling 

 date adult females were randomly selected from the 

 combined catches of several vessels that had been 

 fishing southeast of Block Island, R.I. In addition to 

 the data collected in Rhode Island, 15 immature 

 females were examined. They were collected by the 

 National Marine Fisheries Service on Georges Bank 

 in April 1979. 



All specimens were measured to the nearest 0.1 cm 



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