STUDIES OF ANNUAL GONADAL DEVELOPMENT AND GONADAL ULTRASTRUCTURE IN SPINY-CHEEK CRAYFISH (ORCONECTES LIMOSUS)

Abstract

The aim of this study was to follow the gonadal development in freshwater crayfish Orconectes limosus (Rafinesque) by histological examination of ovaries and testes as well as monthly investigation of the gonadosomatic index over a period of one year. Male gonadosomatic index (IG) ranged between 0.11 to 0.79% with a minimum in July (0.11%) and maximum in September (0.79%) while in females it ranged between 0.25 to 6.15% with a minimum in July (0.25%) and maximum in April (6.15%). Between April and May, the histological dissection indicated presence of mature oocytes and oocytes undergoing resorption. Egg extrusion took place in mid April. During the summer months, the volume of oocytes gradually decreased. In winter and spring, the volume of oocytes began to increase during preparation for egg extrusion. The size of oocytes in the ovary increased from 0.2 mm at the beginning of the reproductive cycle to 1.8 mm immediately before egg extrusion. Average number of eggs in the ovary was 140.8 ± 51.63 (76-290). The ovary was of brown colour for the majority of the cycle, but white in June and July and orange in August and September. Mating started in October and continued through the winter. A difference was found in the proportions of testis and vas deferens in the male reproductive organ during the year. The male gonadosomatic index increased in September during preparation for mating (IG = 0.79%). During the mating season, the male spermatophores were predominantly filled with spermatozoa and sperm was also noted in the vas deferens. Two out of 15 males sampled during the winter were found to be intersex, in which atretic oogonia and oocytes were present at the periphery of testicular tissue and occupied less than 15% of testicular tissue. The evidence of intersex strongly suggested transitional stages of a gradual change of sex, which may be qualified as partial hermaphroditism.