An investigation was carried out in fish landing centers and fish markets adjacent to Kaptai lake, Rangamati to identify the potentiality of fish landing centers, the diversity of available fish fauna and the marketing channel. The study was done by questionnaire interviews (QI) of fish traders, focus group discussions (FGD) and secondary data collection from April 2014 to March 2015 in 03 landing centers and 15 markets of Rangamati district. A total of 84 species of fishes, which consists of 75 finfish and 9 shellfish were identified during the study period. Among 75 finfish, 52 were indigenous freshwater fish species, 10 exotic species and 13 marine species. In shellfish group, 7 prawn and shrimp, 1 crab and 1 pond tortoise species were found. Different types of freshwater fish, marine fish, crustacean and dry fish were found in the investigated markets of Rangamati town. The most abundant freshwater fish species were Catla catla, Labeo rohita, Clarias batrachus, Cirrhinus cirrhosus, Channa punctatus. Few numbers of marine fishes including Latescal carifer, Euthynnus affinis and Mugil cephalus were also recorded. Macrobrachium rosenbergii and Penaeus monodon were found most abundantly during the study period. A total 20 species were threatened according to IUCN red list of Bangladesh including 7 vulnerable, 10 endangered and 3 critically endangered species out of 54 threatened fishes in fresh waters of Bangladesh. Among 7 vulnerable fishes 6 were available, 1 was rarely available. Among 10 endangered species 9 were available and 1 was rarely available. Among 3 critically endangered species 1 species was found available and 2 species were rarely available. Ten exotic fish species (Hypophthalmicthys molitrix, Ctenopharyngo donidella, Cyprinus carpio, Puntius gonionotus, Oreochromis niloticus, Oreochromis mossambicus, Pangasius hypopthalmus, Mylopharyngodon piceus, Aristichthys nobilis and Clarias gariepinus) were found in Kaptai lake during the study period. Fish biodiversity of Kaptailake is decreasing day by day due to habitat degradation and different manmade causes. Proper conservation measures should be taken to protect the threatened fish species from extinction.