**1. Introduction**

Indonesia is the largest archipelagic country in the world which has a high of fish diversity. Djajadiredja et al. [1] estimates the number of fish in Indonesia as many as 4000 species. According to Froese & Pauly [2], there are 4826 species. This number continues to grow along with the discovery of new species. Helfman et al. [3] reported that every year new types of fish are found ranging from 300 to 350 species. Haryono & Gustiano [4] reported that the addition of new types of fish in the world in the 2011–2020 decade was as many as 2904 species with an annual range of 104–448 species and an average of 290 species. The new species in Indonesia, especially for freshwater fish, was reported as many as 15 species in the period 2010–2014 [5].

The number of freshwater fish species in Indonesia is 1248 species [2, 6]. Dudgeon [7] estimated the number could reach 1700 species. The high richness of freshwater fish species in Indonesia is supported by thousands of islands with a diversity of inland aquatic ecosystems. Ambari [8] reported that the area of inland waters in Indonesia reaches 55 million ha which includes rivers, lakes, swamps, reservoirs, and other puddles. The distribution area of this fish is divided into three areas, namely 1) the Sunda Shelf which includes Sumatra, Java, and Kalimantan; 2) Wallacea area or transitional area covering Sulawesi and Nusa Tenggara; and 3) the presentation

of Sahul covering the Maluku Islands and Papua. In the Sunda Shelf and Sulawesi, at least 900 species have been identified [9], while in Papua as many as 400 have been reported [10]. The Sunda Shelf is the center of fish species diversity in tropical Asia, which is rich in endemic fish species. Kottelat et al. [9] reported in detail the level of fish endemicity in Sumatra, namely 11% of 272 species, Kalimantan 38% of 394 species, and Java 9% of 132 species.

Among the freshwaters that are unique physically, chemically, and biologically are peatlands. Pages et al. [11] reported that some peatlands in the tropics are located in lowland areas where there are tropical rain forests with organic material deposits for thousands to tens of thousands of years with a thickness of more than 20 m. Simbolon [12] reported that the area of peatland in Indonesia is around 21 million hectares or about 57% of the total peatland in the world. Indonesia is a country with the largest tropical peat area in the world. The characteristics of waters in peatland areas are very acidic and have a high content of organic material and low levels of nutrients [13]. Peatlans is one of the natural resources that have important hydrological and ecological functions to support life in the ecosystem. On the island of Kalimantan, peatland occurs in coastal and inland areas. According to Soekardi & Hidayat [14], Central Kalimantan has 2,162,000 ha of peatland, ranking third in Indonesia after West Kalimantan and Irian Jaya. The potential of this large area of land is still not widely used, especially for the fishery sector. Blackfish mostly live in flooded lakes or peatlands, and they are resistant to low dissolved oxygen and high temperatures and tend to let the lake ecosystem inundate when the tide is too low. Crayfish migrate from adjacent rivers or permanent water bodies to flooded lakes when floods or monsoons [15, 16]. Some catfishes (pangas, redtail, and shape) are called crayfish, while walking catfish and snakehead are blackfish.

The existence of peatlands plays an important role in storing terrestrial carbon, the hydrological cycle, and maintaining biodiversity. Research on fish in peatland areas in Indonesia has been widely carried out in Tesso Nilo National Park [17], in Perawang, Riau Province [18] and peatlands in Central Kalimantan Province [19, 20]. Based on the research, in general, it shows that the waters in the peatlands area are important habitats for many unique and economically potential fish species. However, the threat to the existence of peatlands and the fish resources in them is getting more serious and has not been handled optimally. Thornton et al. [20] reported that the decline in peatlands in Indonesia is happening rapidly with the loss of peatlands swamp forest which has an impact on decreasing the fish population in the area. Conditions like this will indirectly interfere with the livelihoods of fishermen. Therefore, it is necessary to make conservation efforts for sustainable development. The purpose of the preparation of this manuscript is to reveal the diversity of fish species in peatland waters, their use and contribution nationally, as well as their conservation strategies.
