Jintamas Suwanjarat, Thumronk Amornsakun, Lamai Thongboon, and Piyakorn Boonyoung

pp. 425 - 436

Abstract

The annual reproductive cycle of the total 84 mature male sand gobies Oxyeleotris marmoratus, was
investigated during March 2002 to March 2003. The specimens were obtained from the natural freshwater
marsh in Pattani Province, southern Thailand. The seasonal changes in the testes were determined based on
the histological characteristics during testicular development. The cranial, medial and caudal regions of testis
are synchronously arranged with various stages of germ cells such as spermatogonia, spermatocytes, spermatids
and spermatozoa. The germ cells are found from the periphery to the center of each seminiferous tubule. The
testicular cycle of adult male O. marmoratus can be divided into five stages: resting, developing, mature,
spawning, and spent stages. In the present study, O. marmoratus shows a seasonal cycle of spermatogenesis
with a defined spermiation period. The highest spawning peak occurred in November 2002, and the second
highest peak in May with respectively 100% and 66% of male spawning. Spawning did not take place during
January to March. However, sperm production occurred throughout the year and presented three peaks of
mature stage in April, June, and September. The present work describes the ultrastructure of spermatogenesis with an emphasis on the spermiogenesis. The mature sperm consists of a head without an acrosome, a
short midpiece and a long flagellar tail with lateral fins. The flagellum contains an axoneme of classical form with 9 peripheral double microtubules. The nucleus is symmetrical with a deep basal invagination and the
centriolar complex is located outside the nuclear fossa. Sperm morphology and spermatogenesis between
sand goby and those of the related families are compared.