FISHERY BULLETIN: VOL. 71. NO. 4 



GROWTH 



Young-of-the-year which were first collected 

 in June from shallow eelgrass (Zostera marina) 

 beds in the York River averaged 28 mm in 

 length. Young-of-the-year in the fall of 1970 

 ranged from 88 to 184 mm (Table 2). The 

 November sample came from a culled pound 

 net catch; therefore, 160 to 184 mm is not a 

 true indication of the length range after the 

 first growing season. A better estimate is 83 

 to 195 mm based on lengths of yearlings with- 

 out an annulus taken in April and May with 

 a trawl and from unculled pound net catches. 

 This corresponds closely to the calculated range 

 of lengths at age I for all fish, 90-203 mm (Table 

 1). In December a live 37-mm juvenile was 

 found floating at the surface near the mouth 

 of the York River. Several fish of this size were 

 collected in October on the east side of Chesa- 

 peake Bay during 1968 and 1969 by personnel 

 of Virginia Institute of Marine Science. It is 

 not known whether these small fish were 

 hatched late in the season in Chesapeake Bay 



or were southern migrants from more northern 

 spawning stocks. 



The von Bertalanffy mathematical expres- 

 sion of growth as outlined by Ricker (1958) 

 closely fits the weighted mean length at each 

 age for age groups I to IV (Figure 6). The 

 weighted mean length for age group I was cal- 

 culated from age groups II, III, and IV because 

 commercial gear is selective for the larger fish 

 of age group I. Females were larger than males 

 at all ages. Covariance tests (Ricker, 1958; 

 Mottley, 1941; Snedecor, 1956) on the Ford- 

 Walford lines for males and females indicated 

 a significant difference in the lengths attained 

 by males and females in the first growing 

 season, but the difference in growth after the 

 first season was not significant at the 5% level. 

 The decrease in yearly increment of length was 

 similar for both sexes (Figure 6). 



REPRODUCTION 



Differences between testes and ovaries in 

 vascularization and size became apparent in 



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100 125 150 175 200 225 250 275 300 



100 125 150 175 200 225 250 275 300 



LENGTHS in 5mm INTERVALS 



Figure 5. — Length-frequency distributions of the northern puffer (shaded polygons for each 

 age group: unshaded polygon represents fish from the entire 1970 collection; distribution 

 characteristics for each age group are shown above polygons with calculated lengths above 

 measured lengths). 



960 



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