ROLE OF WATER HARDNESS ON OOCYTE MATURATION OF ZEBRAFISH, DANIO RERIO (HAMILTON-BUCHANAN, 1822)

Abstract

An experiment was conducted to investigate the effect of water hardness on oocyte maturation of zebrafish. Six water hardness levels: Control, 32, 63, 127, 220 and 315 mgl^-1 CaCO₃ respectively were tested in triplicates. Fish of three month old (0.4± 0.001 g) were stocked in 30 I capacity @ 14 fishes / tank and fed with tubifex @ of 3% body weight twice a day (10:00, 17:00 hour) for 60 days. To analyze the microscopic features of ovary 3 fishes from each group were sampled randomly and fixed in neutral buffer formalin (NBF), mounted in paraffin and cut into 6 µ  thick slices and stain with Hematoxylin and Eosin. After 30 and 60 days of rearing ovary was observed for various stages of development (primary growth, cortical alveolus, vitellogenic and mature oocyte). The percentage of different oocyte stages were compared at various level of hardness. When fishes were reared for one month at different hardness levels, the water hardness requirement vary from one stage to another. Low concentration of water hardness (control-32 mgl^-1 CaCO₃) is required for primary growth stage and cortical alveoli stage and high concentration (315 mgl^-1 CaCO₃) for vitellogenic stage. The water hardness at 127 mgl^-1 CaCO₃ is required for mature stage. When fishes were reared for two months period primary growth stage was highest at 220 and 315 mgl^-1 CaCO₃, and water hardness does not seem to show any significant effect to other stages except atretic stage which observed highest at 63mgl^-1 CaCO₃.

 

Keywords: Maturation, Zebrafish, Water hardness, Oocyte.