Seasonal and Age-Related Variations in the Ovaries of Labeo rohita (Hamilton, 1822): A Detailed Gross and Histological Study of Gametogenesis, Maturation and Fecundity

摘要

Seasonal and age-related variations and pattern of oocyte development in the ovaries of female Labeo rohita (rohu) were studied during the age of 18-29 months (first maturation cycle). The experiments were conducted from November 2006 to October 2007. Six gross ovarian stages (virgin/immature, developing, early maturing, ripening, mature-gravid and regressing) were defined and photographically discerned. Ovaries were preserved in 10% buffered formalin and histological development followed with age and season. Results showed that Labeo rohita is a heterosexual fish. Ovaries are paired structure, Joined by a short oviduct. Ovaries were fully developed in June when GSI was the highest (22.73 +/- 0.94). Various developmental stages of oogenesis i.e., chromatin nucleolar stage, perinucleolar stage, yolk vesicle (cortical alveoli stage) and vitellogenic stage were observed and characterized. No spawning or postovulatory follicle (POF) was seen. In August, September and October atretic follicles were quite common. Absolute fecundity determined in June, when GSI and oocyte size was maximum, was 469.93 eggs/gram body weight and 2012.55 eggs/gram ovary weight of fish having an average body weight of 1738.76 gram. Environmental parameters including temperature, photoperiod and rainfall appear to affect the growth and development of ovary. Growth of oocytes was triggered by increasing temperatures and photoperiod. This is the first detailed and systematic study on the reproductive tactics of female Labeo rohita in Pakistan and the results have been discussed in the light of available literature on the reproductive biology of fish.