Diversity and Similarity of Flatfishes (Order- Pleuronectiformes) in Mon State, Myanmar

Pleuronectiformes were first named in 1758 by Linnaeus; pleuromeaning "on side" and nectomeaning "swim". Flatfishes are easy to recognize since this is the only group of fishes that is not bilaterally symmetrical. The ventral side of the body is eyeless and white, while the dorsal is dark and has both eyes. They swim by the undulation of the body, and usually remain close to the bottom on the continental shelf.

Flatfishes are one of the important components in several demersal communities around the world. Flatfishes are also important predators in many demersal communities. They may serve as an important link between demersal production and human consumption⁹.

The flatfishes are one of the most important economic groups of marine fishes in Myanmar. From the commercial point of view, all species are locally known as “Khway-Shar”. It yields 2277.35 tones and by percentage, it had 4.41 % of the Myanmar marine fish landings in Yangon, the business city of Myanmar for 2005¹⁰.

The present study area, called Mon state is an administrative division of Myanmar. It is sandwiched between Kayin State in the east, the Andaman Sea in the west, Bago Region in the north and Tanintharyi Region in the south. The land area is 12, 155 km². The state of capital is Mawlamyine. Bordering Bago Division in the south of Sittaung river mouth, Kayin state in the east, Thailand and Taninthayi division in the south and Andaman Sea and Gulf of Mottama in the west, Mon state is situated between Latitudes 14° 52′ and 17° 32′ N and Longitudes 96° 51′ and 98° 13′ E.

Numerous studies have been done on the distribution, abundance and fisheries biology of flatfish in many different places around the world³,⁴,⁵. However, with the exception of a few taxonomic studies, there was no study about that in Myanmar. Therefore, the objectives of this study is to understand distribution, abundance and diversity of flatfishes along the Mon State, Myanmar.

A total of 5 families, including 21 species of flatfishes were recorded in Mon State. The Psettodidae which included 1 genus and 1 species, the Paralichthyidae, which included 1 genus and 2 species, the Bothidae which included 1 genus and 1 species, the Soleidae which included 4 genera and 7 species, the Cynoglossidae which included 2 genera and 10 species were found along the Mon state in this study.

In table 2, Psettodidae was only found in Zee-Phyu-Thaung, Bothidae was only found in Setse and Paralichthyidae was found in Zee-Phyu-Thaung and Setse. Cynoglossidae was found in every station abundantly but Soleidae was found in Mawlamyine, Paung and Thaton. Therefore, it can be inferred Psettodidae, Bothidae and Paralichthyidae can survive in higher salinity than Cynoglossidae and Soleidae. Of seven stations, the most different kind of species were collected in Mawlamyine and the lowest were collected in Thaton.

In addition, flatfishes are caught mostly using bottom trawl nets by fishermen in all stations as the flatfishes are close to the bottom and swim by undulation of the body. Besides bag nets, gill nets, cast nets and drift nets are used for catching flatfishes in some stations. Soleidae appears to be caught mostly by bag nets and cast nets and Psettodidae, Paralichthyidae and Bothidae appear to be caught mostly by bottom trawl nets in Mon State.

Due to sampling limits in this study, potential bias may be an issue, especially as large variations in catch were observed among vessels. However, since our samples were taken randomly from different catches deposited in the market, it was believed such bias was minimized. it cannot be excluded that the possibility that rare flatfish species were under-represented in the study (in terms of their number and abundance) because many of these species are small in size and deposited as trash fish and so could not be examined completely.

Of the total sample number 378 of 21 species in seven stations, samples were obtained the total number of 128 in Mawlamyine, 79 in Kyaikkhami, 29 in Setse, 53 in Zee-Phyu-Thaung, 19 in Belugyun, 48 in Paung and 19 in Thaton (table 3).

The relative abundance of number of species of Mawlamyine is relatively the highest (34%) of all stations. The relative abundance of number of species of Kyaikkhami (21%) is the higher as compared to Zee-Phyu-Thaung. In the same way, the relative abundance of number of species of Paung (12%) is higher than Setse (7%) and the relative abundance of number of species of Belugyun and Thaton are the same with 5% respectively (figure 2A).

Of the total sample number 378 of 21 species, samples were obtained the total number of 36 in July, 41 in August, 75 in September, 86 in October, 88 in November and 52 in December (table 4).

In the figure 2B, the relative abundance 23% in November was the highest month, followed by October 22%, September 19%, December 13% and August 11% respectively. The relative abundance in July is the lowest (9%).

Figure 2.Comparison relative abundance percentage of sample number of flatfish species A) for each station and B) for each month from July to December 2017.

In figure 3A, Mawlamyine was the highest diversity whereas, Thaton was the lowest diversity. Although Paung and Belugyun have the same value of diversity, the richness of Paung is much higher than Belugyun’s richness. It could be possible that there was an individual dominance in Paung station. Therefore, various species are not found there but the number of individual is high.

The similarity in species composition among the stations was analyzed using the Jaccard index for calculating the extent of similarity between pairs of data sets. Cluster analyses identified two assemblages (with a similarity of 14%), which corresponded to the group of Mawlamyine, Paung and the group of Kyaikkhami, Setse, Zee-Phyu-Thaung, Belugyun and Thaton (figure 4A).

Figure 3.A) the differences among station and B) months of Diversity, evenness and richnessamong the six months from July to December 2017.

In figure 3B, October was the highest value of diversity and August was the highest value of richness. Likewise, September was the lowest value of diversity and December was the lowest value of richness. On the other hand, August and November were high value of richness which the values of diversity are low. So, these months can be the result of an individual dominance. In another way, in spite of being high diversity in October and December, their richness is low because there will be various kinds of species in these months but the number of samples are scare.

The similarity in species composition among the months was analyzed using the Jaccard index for calculating the extent of similarity between pairs of data sets. The JI value between August and September and the value between September and November are the same as well as the highest while it is the lowest for the comparison between July and August. Cluster analyses identified two assemblages (with a similarity of 53%), which corresponded to the group of September, November, August and the group of July, December, October (figure 4B).

Figure 4.A) Dendrogram of similarity among the seven stations; B) among the six months from July to December 2017.

Wang et al.⁸ had examined the seasonal dynamics of flatfish assemblage in the coastal waters off northeastern Taiwan. In their study, the Bothidae was the most dominant family, accounting for 81% of the total catch, while the most dominant species was the Pseudorhombuspentophthalmus. Species richness and diversity were high between the end of fall and the end of spring, but low in summer. In contrast, the Cynoglossidae was the most dominant family and the most dominant species was Cynoglossusarelfor the present study. It can be possible due to the geographical differences.

Table 5 shows the number of samples in each station bimonthly. Of the 375 total number of samples, Mawlamyine (128 number of samples) was the highest number station and then the highest number of samples were within September and October. In addition to, the samples could be collected 79 numbers in Kyaikkhami, 29 numbers in Setse, 53 numbers in Zee-Phyu-Thaung, 19 numbers in Belugyun, 48 numbers in Paung and 19 numbers in Thaton. In almost all station, the highest sample numbers were in September and October.

Mon State is more adjacent to the brackish water rather than the marine areas. Therefore, it can be concluded that flatfishes are brackish water or marine species. In the present study, Cynoglossidae was the most abundant among order- Pleuronectiformes. As a result, Cynoglossidae was also one of the important exported fishes in Mon State. Moreover, Mawlamyine was the highest diversity and the most abundant as it is one major city of Myanmar and most of the fishes all around the Mon State are exported to there.

I’m deeply grateful to my dearest parents, U Kyin Aung and Daw Myint Myint San for their kind moral and financial support to reach the goal of this work.

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