Table 1. — Rate of differentiation and growth of ovarian 

 eggs in samples of the slough darter collected in Dismal Creek. 



Fig. 3. — Bottom and side views of the nuptial tubercles on 

 the chin of a male Etheostoma gracile collected .'Xpril 10, 1964. 



Males, like females, are sexually mature by the spring 

 following their hatching, although at a disadvantage 

 because they are smaller and develop their breeding 

 colors later in the spawning season than do older males. 

 Probably many yearling males do not breed. 



Males reach sexual readiness much earlier in the 

 spring than do females. In April males chased and at- 

 tempted to mount females when placed together in 

 an aquariimi, although the females were not ready to 

 spawn for another 1 /a months. 



The Reproductive Cycle in the Female 



The rcj^roductive cycle for the female begins in ear- 

 ly November when the first eggs begin to differentiate. 

 Development is slow, and it is not until March that 

 significant growth in egg size takes place. To have .some 

 basis for measuring egg development, two observations 

 were made on a few specimens collected from mid- 

 Februaiy to early May. First, the percentage of oxarian 

 eggs difTerentiated was estimated. Although the per- 

 centages are based on estimates rather than actual counts, 

 the estimates were consistently made and the percent- 

 ages are comjiarablc. 



The second set of data was gathered by classifying 

 into three categories 100 eggs from a small section ex- 

 cised from the center of the right ovary. The categories 

 arc (i) develo]5ing but less than 0.33 mm in diameter, 

 (ii) 0.33—0.66 mm, and (iii) over 0.66 mm. Those 

 imder 0.33 mm were differentiated but had little appre- 

 ciable growth, those 0.33—0.66 mm were in the process 



of maturing, and those larger than 0.66 mm were nearly 

 full size. At spawning, eggs were about 0.85 mm in 

 diameter. The rate of ovarian differentiation and the 

 de\elopment of eggs to be laid were rapid during March, 

 April, and May (Table 1). 



A relationship exists between rate of egg maturation 

 and size and asre of the fish. Esrsrs differentiate and 

 mature sooner in older and larger females than in young 

 females. Although the eggs of young females developed 

 slowly in early spring, they actually matured faster in 

 late spring; hence, females of all ages were ready to 

 spawn at the same time. 



As the eggs enlarge, the ovaries appear to change 

 color, probably due to yolk and oil formation. In Feb- 

 ruary the o\aries are white, but later become yellow, 

 then yellow-orange as the eggs mature. 



As spawning time approaches, the genital papilla 

 enlarges. It begins enlarging in December or January, 

 but the greatest change occurs in February, March, and 

 April. In 2-year-old females the papilla measures 

 0.9 X 1.1 mm in mid-February but is 1.5 x 2.0 mm 

 by the last of March. The papilla changes shape as 

 it enlarges, developing a bulbous swelling at the base. 



After spawning season the eggs remaining in the 

 ovaries atrophy and the female absorbs them. Break- 

 down begins immediately, and about a month after 

 spawning time the remaining eggs are absorbed, except 

 for the oil droplets, which give the oxaries a bright 

 orange color. By August the ovaries are small and white, 

 except for an occasional yellow spot representing one 

 of the remaining oil droplets. The o\aries iiavc recov- 

 ered by early November, and the eggs for the next 

 breeding season start to develop. 



More than 2.500 eggs are produced in each oxaiy 

 in one season; however, only about 20 percent ever 

 reach mature size and only a few of these are actuallv 

 laid. 



Mating Behavior and Egg Deposition 



The exact stimulus initiating spawning is not knowii. 

 It apparently is not photoperiodicity or temperatinc. 

 for fish collected only a few miles upstream from the 

 study area spawned more than a week earlier than those 

 in the study area. 



