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Species Composition, Seasonal Occurrence and Abundance of Freshwater Fishes in Ayeyarwady River Segment, Sagaing Region, Upper Myanmar

The study was carried out to assess the fish species composition, seasonal occurrence, and abundance at Ayeyarwady River segment, Sagaing Region, upper Myanmar from July 2017 to June 2018. A total number of 52 species of 37 genera distributed among 20 families and 10 orders of freshwater fishes were recorded during the study period. The highest composition of species was observed in the order Cypriniformes and the lowest in Osteoglossiformes, Anguliformes, Beloniformes and Tetraodontiformes . The highest number of species was recorded in October (cool season) and the lowest were noted in June (dry season) during the study period. The highest numbers of individuals was recorded in order Clupeiformes. According to relative abundance value, the four species were noted as very common (Vc), eight species were common (C), and the remaining 39 species were categorized as uncommon species (Uc). Out of the 51 species recorded, 25 species were encountered at every month and the total of five endemic species and one introduced species was observed during the study period.


Introduction
Myanmar is endowed with a rich resource of freshwater and brackish-water fisheries due to its extensive large river systems running North to South and a huge network of river systems in the Ayeyarwady River.
No complete and precise list of all the fish in the Irrawaddy river basin currently exists, but in 1996 it was estimated that there are about 200 species. In 2008, it was estimated that the Irrawaddy ecoregion is home to 119-195 species of fish found nowhere else in the world (endemic). Several new species of fish have been described from the Irrawaddy river basin in recent years (for example, the cyprinid Danio htamanthinus in 2016 and the stone loach Malihkaia aligera in 2017), and it is likely that undescribed species remain (Wikipedia, 2017).
Ayeyarwady River is an important natural shelter for many aquatic flora and fauna which is less studied. The study of freshwater fishes in Ayeyarwady segment may be essential as one of the corner stone for conservation scheme of biological resources in Myanmar. It is hoped that this paper would provide some information for further research work. Thus, the present study was carried out within the specific area with the following objectives, 1) to investigate and record the freshwater fish in Ayeyarwady Segment, 2) to record relative abundance of fishes in the study area.

Collection, Preservation and Identification of Specimens
In this study, collection of specimen was made with the helpfulness of local fishermen. Fish sampling and landings survey were done twice a month. Fish samples were collected in Ayeyarwady segment at early morning and evening. Sample fishes at different species were randomly selected from the catches of different fishing gears in the River. The photographs of fresh specimens were taken by using digital camera.
Measurements were also taken on sample fishes to aid the identification process using keys provided by Day (1878), Lagler (1977), Talwar, and Jhingran (1991), Jayaram (2013), Fish Base (2017. After identification, all fishes were maintained in laboratory of Zoology Department, Shwebo University for later taxonomical revision.

Analysis of Data
Based on the recorded fish species, relative compositions of species in different orders were analyzed. Native, introduced, and endemic fish species were classified among Relative abundance = The average relative abundance was categorized as: Uncommon (uC) = having relative abundance less than 0.0100 Common (C) = having relative abundance of 0.0100 and above but less than 0.0500 Very common (vC) = having relative abundance of 0.0500 and above

Species Composition of Fishes in the Different Orders
A total number of 52 species of 37 genera distributed among 20 families and 10 orders of freshwater fishes were recorded during the study period (Table 1).       Tetraodontiformes (X)

Seasonal Occurrence, Abundance and Relative Abundance of Recorded Fish Species in Study Area
In the present study, a total number of 38 species belonging to 27 genera of 17 families under nine orders were recorded in dry season (from mid-February to mid-June).
Total number of fish caught (9153) were recorded and recorded percentage (3%) was found during the study period (Table 2 and Figure 3).
In the present study, a total number of 52 species of 37 genera distributed among 20 families and 10 orders of freshwater fishes were recorded. Among the recorded data, the highest composition of species was observed in the Order Cypriniformes (36%) and the lowest each (2%) in Osteoglossiformes, Anguliformes, Beloniformes, and Tetradontiformes respectively.
Cypriniformes is an order of ray-finned fish, including the carps, minnows, loaches and relatives. This order contains 11-12 families, over 400 genera, and more than 4,250 species. They are most diverse in southeastern Asia, and are entirely absent from Australia and South America (FishBase, 2004). Since Myanmar is a country located in Southeast Asia region and much of the environmental conditions were almost the same in these regions, most species was recorded in Order Cypriniformes in present study and this finding was agreed with that of FishBase, 2004. Moreover, many local researchers also found that the species composition in order Cypriniformes was the largest in different study sites (Htay Htay Sein, 2010) andNwe Ni Saw (2013). It was noted the species recorded under this order, such as Cirrhinus marigala, Labeo rohita, L. calbasu, L. angra, L. bata, Amblypharyngodon atkinsonii, Osteobrama belangeri and Lepidocephalus thermalis were economically important as their daily food for local people of Myanmar.
According to FishBase (2017), the total of 3 species was noted in Order Osteoglossiformes, 3 species in Order Anguilliformes, 10 species in Order Beloniformes and 4 species in Order Tetraodontiformes respectively in Myanmar. In the present study, only one species in each order was recorded. According to the recorded data, the highest number of fish species (48 species, 38%) was recorded in cool season and the lowest (38 species, 30%) in dry season. It was also noted that, 25 species were encountered in all seasons while Anguilla bengalensis was encountered only once in November in cool season and the rest of 25 were recorded as not continuously.
Based on the relative abundance, very common (vC), common (C) and uncommon (uC) were classified. In dry season, among 38 species, five species were recorded as very common (vC), seven species as common (C) and 26 species as uncommon (uC). The highest number of individual (2820) with relative abundance (0.273494) was recorded in Amblypharyngodon atkinsonii and the lowest number only two with relative abundance (0.000194) in Bagarius yarrelli.
Out of 40 species, five species as very common (vC), eight species as common (C) and 27 species as uncommon (uC) were recorded in wet season. The highest number of individual (23359) with relative abundance (0.3386) in Barilius gatensis and the lowest number of individual only two; relative abundance (0.000) in the species Bagarius yarrelli was noted in wet season. According to the IUCN Red List (2017) the Bagarius yarrelli was near threatened species but these species were collected every season in the study area.
In cool season, three species were recorded as very common (vC), seven species as common (C) and 37 species as uncommon (uC) in 48 speies. The highest number of individual (112900) with relative abundance (0.3908) was noted in the species Gudusia chapra and the lowest number of individual only one with relative abundance (3x10 -6 ) in the species Anguilla bengalensis at cool season. This species was collected only one specimen throughout the study period. Among the three seasons, the highest number of fish was recorded in cool season and lowest in dry season, because it was depended on the water level and some environmental factors in study area. Findings of this study will be very helpful to conserve this unique natural habitat of fish, diversity and other fauna.

Conclusions
The Ayeyarwady River supports diverse and abundant population of freshwater fishes in Myanmar. The flood plains of the Ayeyarwady River are highly productive and play on important role in the ecology of the river system. These characteristics could probably create suitable niches for a variety of fish species and subsequently higher fish abundance will be found in that habitat and also habour five endemic species, the study area need to be maintained sustainable yield.