Describing Squamatological Variation between Sexes of Mesopristes Cancellatus (Cuvier, 1989)

Christina A. Barazona 1, Mark Anthony J. Torres 1, Jessie J. Gorospe 2 and Cesar G. Demayo 1

1 Department of Biological Sciences, Mindanao State State University- Iligan Institute of Technology, Iligan City, Philippines

2 School of Graduate Studies, Mindanao State University- Naawan Misamis Oriental

Abstract. Geometric and morphometric analysis have been a helpful tool in identifying and establishing variations among squamatological scales of Mesopristes cancellatus. Traditional descriptive paired with landmark-based analysis verifies the specific variance among scales collected under the pictoral fins in terms of its shape, size, anterior and posterior end, focus position, type of radii and circuli appearance.

Keywords: Landmark-based analysis, Squamatology

1. Introduction Mesopristes cancellatus (Cuvier,1898) also known as Tapiroid grunter is a protrandous tropical fish

rarely found in brackish and fresh water environments in Indonesia, New Guinea, Vanuato, Taiwan, Japan, and Philippines. This species is highly priced in markets because of its delectable taste. Recently the average catch of the said species has been decreasing and populations of this fish is believed to be in danger of extinction due to uncontrolled and unregulated harvesting [1]. It is believed that there are morphological variations in this species of fish depending on where they inhabit. There is therefore a need to describe and properly identify this species for conservation and protection purposes. Several methods are available in describing fishes and one of which is through a close examination of their scales. Many studies described only a few scales within fish species thus a detailed examination of the scales in the body of the fish should be done.

Scales are the most external part of majority of fish’s body and are used for protection, coloration and sensory receptors. Fish scales have been helpful as taxonomical characters in identifying fishes [2], age determination [3], past environmental experiences such as polutions [4], population structures, migration, pathology and other growth issues [5]. Squamatology, the study of scales helps in identifying the characterisics of fish scales. Thus it has been a helpful ground in classifying fishes taxonomically, genetically, and behaviorally. Anthropogenic activities such as overfishing, habitat degradation and aquatic pollution have caused threats and gradually decrease the abundance of icthyofaunas [6]. A concrete examination of fish scales is needed to obtain current environmental and behavioural status of species. Qualitative and quantitative analyses of scale shapes are important to have a good bases for the nature of the species.

Adams and colleagues [7] noted that the analysis of shape is a fundamental part of biological researches. Geometric and morphometric methods provide sophisticated data analysis in comparing the anatomical features of organisms. In this study, qualitative and landmark-based geometric morphometric analysis were used in describing the relationship, shape and orientation among anatomical variables of the scales coupled with relative warp analysis and multivariate analysis [7].

2. Materials and Methods

2012 2nd International Conference on Environment and BioScience IPCBEE vol.44 (2012) © (2012) IACSIT Press, Singapore

DOI: 10.7763/IPCBEE. 2012. V44. 18

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M. cancellatus fish samples were obtained from Tagoloan River, Misamis Oriental from October- December 2011 (Figure1). A total of five specimens per sex were caught and describedin this study. The scales were collected using a fine forcep. Scales under the pictoral fins were sampled for a greater chance of obtaining original scales. These were randomly selected both from the right and left side of the specimen’s body. Eighteen to 26 scales were obtained from each of the specimen, air dried and and gently sonicated with a dilute solution using a laboratory grade detergent. Remaining tissues were scraped off from the scales [8].

Fig. 1: A-B: photograph of M. cancellatus sampled from Tagoloan River. 1A male specimen; 1B female specimen,

showing the actual scales and orientation under the pictoral fins.

Cleaned scales were allowed to set in fresh water. When scales became flexible, excess water were removed and mounted between glass slides where both edges were sealed with an invisible tape. Scales were kept moist to avoid coiling and fractures [8]. Prepared slides were examined using a stereomicroscope under low magnificattion and the images taken using a Sony DSC-T200 digital camera. Images were saved, labeled and numbered for further qualitative and quantitative description.

General discriptions and codes assigned in classifying scales are shown in Table 1. Scale characteristics include (1) overall shape; (2) size; (3) shape of the anterior margin; (4) shape of the posterior margin; (5) focus position; (6) type of Radii; (7) apperance of the circuli. Data was subjected to mutivariate analysis to obtained principal components and presented in a scatted plot for groupings and distributions of scale shapes between sexes.

Table 1: General morphological characteristics of scales.

Scale description Type Respective code Scale shape Rectangular 0 Square 1 Oval 2 Triagular 3 Hexagonal 4 Scale size Small (sm) 0 Medium (med) 1 Large (lar) 2 Shape of the anterior margin Crenated, Obcordate (C-O) 0 Crenated (C) 1 Shape of the posterior margin Tongue-like (TL) 0 Wave (W) 1 Focus position Posterirly located (PL) 0 Centrally located (CL) 1 Type Radii Presence of Primary Radii (PR) 0 Presence of Secondary Radii (SR) 1 Presence of Primary and Secondary Radii

(PR-SR) 2

Circuli appearance Continous, Disrupted (CoD) 0 Discontinous, Disrupted (DiD) 1

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Thin-plate spline software series were used for biometric verification [9]. Files and images were built in tpsUtil program, landmarks were digitized with tpsdigw32 and shapes were summarized in tpsRelw program [10]. Landmark coordinates were modified from protocol prepared by Ibanez et. al. [11]. Nine landmark points were identified according to the shared features of all the scale scales (Figure 2C). Landmark points 1 and 7 are width of the posterior origin embedded to the flesh of the fish; points 1 and 3 are points assigned to the longest length on the left of the scale while points 7 and 5 on the right; points 3 and 5 is the width of the scale on the anterior end and points 2 and 6 measures the longest width of the scale in the middle; points 8 and 9 is the distance between the origin of attachment to the focus and points 9 and 4 is the distance from the focus to the anterior margin.

Fig. 2: A-C Typical ctenoid scale found under the pictoral fins. Scale morphological features: Anterior Field (AF),

Poster Field (PF), Anterior Margin (AM), Posterior Margin (PM), Primary Radii (PM), Secondary Radii (SR), Circuli Rings (CR), Focus (F).

3. Results and Discussion Of the 212 scales collected, 20 different scales were described from among the male samples (Figure 3A)

and 23 from among the females (Figure 3B).

(A)

(B)

Fig. 3: A,B: Photographs of the scales. 4A.1-4A.20 different types of scales from the male fishes; 4B.1-4B.23 different scales from the female samples.

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Scales obtained from both males and females of M. cancellatus are mainly ctenoid scales which are characterized with sharp spines at the posterior end of the scales. Two types of foci were observed- one that is posteriorly located and the other centrally positioned; both, however, are distinct and can easily be seen. Scales are also characterized by a distict primary and secondary radii. Radii are thick and well patterned grooves all the way to the anterior end. From the focus, lines of growth develop into ridges, the circuli [10]. Circuli among the scales were observed to be compressed, thin, numerous, continuous, patterned but disrupted as it approaches along the radii grooves, the same in all the scales of both sexes. This means that circuli patterns are conserved to both male and female of M. cancellatus. This may account to the consistency of developmental patterns particularly its growth. Only very few among scales have distinguishable annular rings, thus this characteristics were not included in the general descriptions of the scales.

Close inspection of the scales revealed that only six morphological characteristics are found to be common in both sexes (Table 2). The scatter plot in Figure 4 groups the scales based on similarities in overall characteristics. Male scales are grouped into 10 major types of scales (Figure4A) while 11 for the female scales (Figure 4B). The plots shows that the scales from the males samples were more variable as the points are more scattered when compared to that of the females. The scatter plot of the pooled data from both sexes grouped the scales into 17 major types. Of these, five are shared by both sexes (Figure 4C).

Table 2: Characteristics of the scales collected from male and female specimens of M. Cancellatus.

Scale characteristics Sex Sex Rec, sm, C-O, TL, PL, PR, CoD M,F Sq, sm, C-O, TL, PL, PR, CoD M,F Rec, sm, C, TL, PL, PR, CoD M,F Sq, sm, C, TL, CL, PR-SR, CoD M,F Rec, med, C-O, TL, PL, PR, CoD M,F Sq, sm, C-O, TL, CL, PR,SR, CoD M,F Rec, med, C-O, TL, CL, PR, CoD M,F Sq, med, C-O, TL, CL, PR, SR, CoD M,F Sq, sm, C, TL, PL,PR , CoD M,F Sq, med, C, TL, PR, SR, CoD M,F Sq, med, C-O, TL, CL, PR, CoD M,F Sq, med, C, TL, CL, PR, CoD M,F Ov, sm, C, TTL, PL, PR, CoD M,F Sq, med, C, TL, PL, PR, CoD M,F Rec, sm, C-O, TL, CL, PR, CoD M Sq, sm, C-HS, TL, CL, PR, CoD M Rec, sm, C, TL, CL, PR-SR , CoD M Sq, med, C, TL, PL, PR, CoD M Rec, med, C, TL, CL, PR-SR, CoD M Sq, lar, C, TL, PL, PR, CoD M Rec, sm, C, TL, CL, PR-SR, CoD F Sq, lar, C, TL, CL, PR, CoD F Rec, med, C, TL, PL, PR, CoD F Sq, lar, C-O, TL, PL, PR, CoD F Rec, med, C, TL, PL, PR-SR, CoD F Sq, lar, C, TL, PL, PR, CoD F Rec, med, C, TL, CL, PR, CoD F Ov, med, C, TL, CL, PR, CoD F Rec, lar, C-O, TL, CL, PR, CoD F Ov, med, C, TL, PL, PR, CoD F Rec, lar, C-O, TL, PL, PR, CoD F Tri, med, C-O, TL, PL, PR, CoD F Rec, lar, C, TL, PL, PR, CoD F Tri, sm, C, TL, PL, PR, CoD F Sq, med, C, TL, CL, PR-SR, CoD M Hex, med, C, TL, PL, PR, CoD M

M (male), F (female

Fig. 4: A-C: Scatter plot of the distribution of the scale types with reference to 7 morphological characteristics. 5A male classification of scale types showing 10 groups; 5B female classifications of scale types showing 11 groups; 5C pooled

showing 11 major groups both male (inverted triangle) and female (square), scale types.

Shape varation represented by the relative warps shows four significant variation in male and female scales. The grids shows variation in the position of the foci. Variations among the scales are also attributed to detectable differences in the overall shapes of the scales that vary from being large and broad to being small

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and narrow. There is also pronounced variation in the shapes of the anterior and posterior ends of the scales from being depressed to being extended anteriorly. Disparity can also be observed when the distance between the foci and the posterior ends of the scales are measured. This might be brought about by differences in the rates of growth of the scales [11]. The scale foci are said to be the first to be formed during ontogenesis [5] and its shape remains consistent throughout the entire lifespan of the fish [13].

4. Conclusion There is considerable variation in the characteristics of the scales observed although collection was

limited to a single region of the fish body, which includes those found under the pictoral fins. There are scale types that could be used to discriminates the sexes of M. cancellatus. The application of the landmark- based analysis geometric morphometric analysis has been useful in establishing dimorphism in M. Cancellatus and reinforced the findings that males and females can have different types of scales.

Fig. 5: Transformation grids of mean shapes from relative warps of (a) Male and (b) female M. cancellatus.

5. Acknowledgements This study have been made possible through the assistance of the Department of Science and Technology

for scholarship grants, Office of the Mayor and Municipal Engineering Department of Tagoloan Misamis Oriental for the permits and the Department of Agriculture Tagoloan Misamis Oriental chapter for relevant information.

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