de VLAMING: CONTROL OF REPRODUCTION IN GILLICHTHYS 



High temperatures bring about ovarian regres- 

 sion by inhibiting vitellogenesis and causing 

 atresia of all yolky oocytes. In males, high tem- 

 peratures apparently increase the rate of mei- 

 otic divisions and the process of spermiogenesis; 

 this is apparent because the testes of fish sac- 

 rificed soon after the initiation of high temper- 

 ature treatment are characterized by large num- 

 bers of secondary spermatocytes and spermatids. 

 Fish sacrificed after longer treatments at high 

 temperatures, however, are characterized by 

 testes with only primary spermatogonia, sug- 

 gesting that high temperatures inhibit the trans- 

 formation of spermatogonia into primary sper- 

 matocytes. High temperatures also cause the 

 "flaking oflF" of cysts of spermatocytes from the 

 germinal epithelium into the lumen of the tes- 

 ticular lobules. Moreover, pyknotic degeneration 

 of spermatocytes, spermatids, and spermatozoa 

 occurs at high temperatures, followed by phago- 

 cytosis of cellular debris. Mitotic proliferation 

 of spermatogonia is inhibited above 25°C, but 

 treatment at 27°C for 15 days does not inacti- 

 vate the sperm remaining in the testes. Weisel 

 (1948) showed that the spermatozoa of Gillich- 

 thys remain alive in vitro for 2 weeks at 2°-4°C, 

 but at 24°-26°C they are immobile in 33 hr. 



In Gillichthys the termination of the reproduc- 

 tive season is apparently not endogenously timed. 

 Regression is not "obligatory" since low temper- 

 ature treatments (regardless of photoperiod) 

 prevented gonadal involution at the "normal" 

 time (July). These studies imply that the re- 

 productive cycle of this species is primarily 

 under exogenous regulation. A similar situa- 

 tion has been reported in the cyprinodontid, 

 Epiplatys bifasciatus which occurs in the Zio 

 River and Lagoon of Lome of the Republic of 

 Togo, Africa (Loiselle, 1969). Gillichthys is 

 thus apparently a potentially continuous breeder 

 but has a reproductive cycle imposed upon it by 

 the increased temperatures of summer. Al- 

 though little information is available on the 

 causes of termination of reproductive cycles, 

 differences are evident. For example. Bagger- 

 man (1957) suggested that since none of the 

 experimental conditions she tested could main- 

 tain continuous breeding in Gasterostetis acule- 

 atus, termination of the cycle is endogenously 



controlled. The rate of postspermatogonial re- 

 gression is also accelerated by warm tempera- 

 tures, and low temperatures retard the rate of 

 sexual regression in F^mdulus heteroclitus 

 (Lofts, Pickford, and Atz, 1968). 



GONADAL RECRUDESCENCE 



In Gillichthys gonadal recrudescence does not 

 occur at constant temperatures of 24°C or above, 

 regardless of photoperiod. Long-term experi- 

 ments indicate that gonadal recrudescence is not 

 initiated in males or females after nearly 4 

 months at high temperatures (comparable to 

 summer temperatures). High temperatures 

 also retard the early phases or intermediate 

 phases of gametogenesis in Fundulus heterocli- 

 tus (Burger, 1939), Phoxinus laevis (Bullough, 

 1939) , female Apeltes quadracus (Merriman and 

 Schedl, 1941), Enneacanthus obesus (Harring- 

 ton, 1956), female Fundulus confluentus (Har- 

 rington, 1959), Couesius plumbeus (Ahsan, 

 1966), and Cymatogaster aggregata (Wiebe, 

 1968). 



Experiments, begun in winter and spring with 

 the longjaw goby in phases of active gameto- 

 genesis, indicate that gonadal activity is main- 

 tained at 20°C over a wide range of photoperi- 

 ods; long photoperiods may be more eff'ective 

 in this regard, but more experiments are needed 

 to prove conclusively the influence of photoperi- 

 od. Beginning in July with fish having regres- 

 sing testes, mitotic proliferation of spermato- 

 gonia was stimulated, especially with a short 

 photoperiod, but complete recrudescence did not 

 occur at 20°C. However, beginning in August 

 with fish having regressing testes, recrudescence 

 did occur at 20°C; a short photoperiod was more 

 eflfective in this respect. Beginning in Septem- 

 ber, testicular and ovarian recrudescence is in- 

 itiated at 21°C, but only with a short photoperi- 

 od. The rate of spermatogenesis was, however, 

 extremely low at these temperatures. Thus, a 

 shift in gonadal responsiveness to 20°C appar- 

 ently occurs between July and August. The ex- 

 periment beginning in July was continued for 3 

 months without the initiation of spermatogenesis 

 whereas the experiment beginning in August 

 was terminated after a much shorter time. The 



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