Investigations on the surface ultrastructure of scale of Geno tooth-carp, Aphanius ginaonis (Holly, 1929) (Actinopterygii: Cyprinodontidae) using scanning electron microscope

Study of scales of 44 Aphanius ginaonis (Holly, 1929) specimens including 28 males and 16 females revealed that the index of relative length of scale in male and female specimens were 3.41 and 3.63 respectively and female scales were significantly larger than male scales (p<0.05). The index of relative width of scale was 3.795 in males and 3.82 in females indicating no significant differences. SEM studies showed presence of fine conical shape structure at the posterior end of the scales hence this scale is a fine ctenoid scale characterized by weak ctenii. The focus of the scale is clear and sharp located almost in the centre. Primary radii which originate from very near the focus divide the anterior position of the circuli into compartments. The radii are absent laterally and posterially. Originating far away from the focus, the secondary radii are seen. The scanning micrographs showed the presence of definite teeth-like structures on the anterior and lateral circuli. These are known as lepidont. The lepidonts have either conical blunt ending or bear a hook. At the posterior edge circuli end and round granules called tubercles are formed called tubercles. These are arranged in U shape fashion. At the posterior most end of the scale, the tubercles are replaced by conical projections of different size which are named ctenii. The skin covering the posterior field of scale is perforated by a number of pores of different diameter. These pores probably indicate the position of mucous cells situated in the epidermal layer. A distinct break in the circuli points towards the formation of an annulus is observed. The annuli indicate the fish age. Age determination and study of growth factors of this endemic and rare species will be useful in the population dynamic studies helping in its conservation.