Morphometric variations of tropical eel Anguilla bicolor (McClelland, 1844) harvested from different locations within Aceh waters, Indonesia

Anguilla bicolor is a commercial and predominant species within the eels group in Aceh waters. The objective of the present study was to analyze the morphometric variation of the A. bicolor collected from three different locations in Aceh waters, Indonesia. A total of 18 individuals of fish samples (6 individuals from every location) were measured for traditional-truss network morphometric characters. The univariate (ANOVA) analysis showed that the morphometric of the three eel populations were not significantly different (P > 0.05). Multivariate (Discriminant function analysis, DFA) analysis was successfully grouping three eel populations into three groups, where A. bicolor SKL and A. bicolor TB were more similar than A. bicolor KJU populations.

Aceh Province, Indonesian. This information is important to plan a better conservation strategy of the eel in Aceh waters in the future.

Sampling procedure
The eel was collected using a trap and hand-line, then placed on the waters (rivers and ponds) from 6 PM to 6 AM. The soil worms, chicken intestines, and fish were used as the bait.
The sample of eels was measured in length (total length (PT) and standard length (PS) using digital calipers (Mitutoyo, CD-6CS. Error = 0.01 mm), and weight also be measured using a digital scale (Toledo, AB-204. Error level = 0.01 g). Measurement of morphometric characters will be conducted in the laboratory after the sample is preserved using 10% formalin solution.

Traditional morphometric
Traditional morphometric measurements refer to Hwang et al. [17] (Figure 1). The measurement method is as follows:  PFL Pectoral fin length The distance from the origin of the pectoral fin to the tip of the longest pectoral-fin ray. 10 ML Mouth length The distance from the tip of the to the last of the lip. 11 SnL Snouth length The distance from the tip of the snout in the middle of the upper lip to the anterior rim of the orbital. 12 DFBL Dorso fin base length The base length between the first and the last ray of the dorsal fin. 13 AFBL Anal fin base length The base length between the first and the last ray of the anal fin.

Truss morphometric
The truss network morphometric was employed in this study. This technique is used to measure the fish's body by connecting predetermined diagonal points (homolog points), both horizontally and vertically [18]. The measured morphometric character aims to analyze the extent of the closeness or similarity of the morphological among the samples from different locations or populations [19] ( Figure  2).

Univariate analysis of traditional-truss morphometric
The ANOVA test showed that sampling location as representative of the population did not give a significant effect on traditional and truss morphometric character variation (P>0.05). Therefore, the Duncan multi-range test showed that the morphometric characters both traditional and truss of the three eels were not significantly different (P > 0.05) among the population (Table 3 and 4). It means that the traditional morphometric characters of A. bicolor from Singkil, Kajhu Aceh Besar, and Tibang Banda Aceh are identic. But, only one truss morphometric character was significantly different (P <0.05) between A. bicolor from Singkil and A. bicolor from Kajhu populations, namely D character (the distance from the curve of the upper tail stem to the tip of the tail).

Multivariate analysis of traditional-truss morphometric
The discriminant function analysis (DFA) of traditional and truss morphometric produces two functions. The first function of traditional morphometric has an eigenvalues value of 24.602 with a percentage variance value of 96.37%, while the second function has an eigenvalues value of 0.925 with a percentage variance value of 3.625% (Table 5). The eigenvalue of the second function is less than 1, where the contribution of morphometric characters to this function can be neglected. The first function of truss morphometric has an eigenvalues value of 27.391 with a percentage variance value of 94.11%, while the second function has an eigenvalues value of 1.715 with a percentage variance value of 5.89% ( Table  5).
The traditional morphometric characters that contribute to the second function are only one character, namely ML (the distance from the tip of the to the last of the lip), while the other morphometric characters contribute to the first function. A total of nine truss morphometric characters that contribute  to the first function, namely; A (the distance measured from the tip of the head to the curve of the top of the head), B (the distance from the curve of the top of the head to the beginning of the dorsal fin), D (the distance from the curve of the upper tail stem to the tip of the tail), F (the distance from the curve of the lower caudal shaft to the beginning of the anal fin), G (the distance from the start of the anal fin to the crease of the gills), H (the distance from the fold of the gills to the tip of the head), J (the distance from the curve of the top of the head to the beginning of the anal fin), K (the distance from the start of the dorsal fin to the crease of the gills) and N (the distance from the curve of the upper tail stem to the indentation of the lower tail stem), while the other morphometric characters contribute to the second function.
The scatter plot of traditional and truss morphometrics was successfully grouping the three fish populations into three groups based on each eel population (Figure 3), where the Singkil population closely to Tibang population, and the Kajhu population was distinguished separately. Therefore, the results of the DFA analysis confirmed that the A. bicolor SKL and A. bicolor TB were more similar than A. bicolor KJU populations. These results confirmed that truss morphometric analysis is more reliable and sensitive compared to traditional morphometric analysis. Similar result was also reported by Muchlisin et al. [21,22] in the Rasbora group at the Lake Kaut Tawar, Aceh Province, Indonesia.
An intra-species variation on the morphology of fish species can be influenced by environments condition and populations, as detected in naleh fish (Barbonymus sp.) [23] and mullets [24]. Similar findings were also found in several species such as morphometric variations in two populations of Sander lucioperca at fragmented areas, Rhone River, France [25], morphometric variation among Sardina pilchardus populations from the Northeastern Atlantic and the Western Mediterranean [26], and morphometric variation between Pomatomus saltatrix in the Black, Marmara, Aegean, and Northeastern Mediterranean Seas [27].

Conclusion
The morphometric of the three populations of eel in Aceh waters are highly similar or identic, however, A. bicolor SKL and A. bicolor TB has closely related to A. bicolor KJU populations.