Aquaculture is concerned with the propagation and rearing of aquatic organisms. Many people are turning to aquaculture to improve the food production and to contributes for economic development. The present investigation, water sample and infected fish (Catla Catla) were collected in cultural pond from saliyamangalam. Analysis of Physicochemical parameters in water sample and fungal populations were studied in skin, Gill fin and gut of Catla Catla by using fungal culture medium. From the water quality analysis it clearly indicates that, changes in temperature, low oxygen level, low alkalinity, high organic load, decreased level of nitrite. Fungal studies clearly indicate that there was no fungal growth in control plate the various in infected fish tissue sample inoculated plates were showed significant growth of fungal colonies, such as Achly Sp; Pencillium sp Aspergillus Sp, Exopila, Branchiomyces, Saprolegliasis, Icthyophonus, Fonsecaea, found in predominantly. From the present study it was concluded that fungal pathogens are most significant microbial agents affecting freshwater fishe (Catla Catla) and climatic change may play a grate role in modulating the occurerence of fungal fish diseases.