96 Reproduction, Competition, and Predation 



were smaller than average, the numbers of fry produced were larger than 

 average. ^^ Mraz and Cooper ^^ also found little correlation between the 

 number of brood fish stocked in ponds and the strength of the resulting 

 year classes (Figure 5.1). 



Age and Sexual Maturity 



The age of a fish at the time of sexual maturity varies with its size and 

 the latitude of its habitat. According to Swingle and Smith/*" bluegills as 

 small as one-half ounce have been known to spawn when 1 year old (in 

 Alabama) and where food was extremely plentiful, young bluegills 

 weighing 2 ounces spawned when only 5 months old. Largemouth bass as 

 small as 6 ounces and crappies as small as 2 ounces have been known 

 to spawn when 1 year old (Alabama). 



Eschmeyer -^ stated that some of the largemouth taken from the Clinch 

 River below Norris Dam (Tennessee) would probably have spawned 

 at 1 year of age. 



Farther north in central Illinois, James ^^ making a histological study of 

 the gonads of largemouth bass and bluegills concluded that while a few 

 male bass produced small numbers of sperm at 1 year, none of the females 

 produced mature eggs. Many of the yearling bass that James studied 

 were more than 10 inches in length and weighed 0.50 to 0.60 pound each. 

 The larger and medium-sized 1-year-old bluegills produced mature eggs 

 or sperm, but those less than 2 inches contained only small oocytes, in- 

 dicating that they were sexually immature. 



North American centrarchids imported to South Africa have had their 

 seasons reversed and some showed rapid attainment of sexual maturity.^^ 

 Smallmouth bass reproduced at 17 months and bluegills at 7 months 

 when their seasons were reversed south of the equator. These fish orig- 

 inated in Maryland and Ohio. 



In the north central states, most of the common game and pan fish 

 require one year (bluegill, rock bass), two years (crappie, largemouth, 

 smallmouth), or three years (northern pike, walleye) to reach sexual 

 maturity. The age of a fish at sexual maturity is important in planning 

 stocking rates for new or renovated lakes or ponds. 



Sex Ratios 



Most studies of sex ratios of the individuals composing isolated popula- 

 tions of fresh-water fishes have shown that more males than females are 

 to be found among the young of the year, but among older fish the 

 dominance of females was so great as to leave little doubt that the males 

 die off much faster than females. This is not only true in the pike and 

 perch families but also in some of the nest-building centrarchids.^^ 



