Time dependent ultrastructural alterations on the skin, eye, barbel and fins of the spawn of Clarias batrachus (Linn. 1758) exposed to UV-B radiation

Abstract

Present study highlighted the ultramicroscopic (SEM) alterations of the skin, eye, barbel, and fins of spawn of an air-breathing teleost (Clarias batrachus, Linn. 1758) induced by UV-B radiation (280-320 nm) at a dose (@4.07 × 10^-20J/photon/m²) under the time-frame of 5, 10 and 15 min/d in the laboratory condition for the periods of 5 and 10 days. Limnological parameters revealed no significant changes throughout the period of experimentation which were measured by PCS Testr 35 Multi-Parameter. Morphometric analysis revealed that during the extended exposure period of 10 days the spawn size and weight were reduced as analysed through Specific Growth Rate (SGR). SGR values in terms of weight for 5 and 10 days under 3 time-frames were 17.12%, 12.52%, 11.46% and 9.09%, 6.43%, 6.09% respectively, which revealed a declined trend along with the exposure days. In the skin of C. batrachus, the compact regular orientation of the stratified epithelial cells and mucous cells became distorted and the microridges and double-ridged structures showed destruction and fragmentations. The body striations and microfolds became shrinked and swollen and finally degenerated to form a mass. The distribution of mucous cells throughout the epidermis was disorganised and releasing secretory contents on the surface through small pores. Appearance of huge quantity of biogenic semi-hexagonal plate like crystals (guanine platelets) on the skin surface of the body was the most significant observations during UV-B radiation. In the developmental phases the eyeball showed shrinkage loosing normal regular concave structure and to become a dome-shaped one. The supportive connective infoldings became loosened. The choroid coat displayed deformities and the iris deformed the pupil. The fibroblast on the epithelium and melanocytes depicted dispersed arrangement. The pairs of ventral barbels near the mouth depicted the presence of taste buds that became severely damaged exposing the sensory as well as neuroepithelial cells. Compact regular arrangement of the SECs was completely destroyed leaving long and deep channels inbetween them; the disintegrated concentric MRs also showed a mass.

Keywords: Barbel; Clarias batrachus; Eye; Fin; SEM; Skin; UV-B radiation.