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Comparative scale morphologies in common freshwater fishes of Peninsular Malaysia – A case study

Conference Paper · November 2016 DOI: 10.1063/1.4966850

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Citation: AIP Conference Proceedings 1784, 060012 (2016); doi: 10.1063/1.4966850 View online: http://dx.doi.org/10.1063/1.4966850 View Table of Contents: http://scitation.aip.org/content/aip/proceeding/aipcp/1784?ver=pdfcov Published by the AIP Publishing

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Comparative Scale Morphologies in Common Freshwater Fishes of Peninsular Malaysia – A Case Study

Farah-Ayuni, F.a), Muse, A. O., Samat, A. and Shukor, M. N.b)

School of Environmental and Natural Resource Sciences, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia

Corresponding authors: a)[email protected]; b)[email protected]

Abstract. Hard plates covering fish body or scales, do not only serve as external protection, but are also important as one of the tools for species identification. This study was designed to recognise morphological characters of fish scales that can be used for identification and to comprehend the inter-specific variations of scales from different species by using selected indices from scale measurements; L1/1, L2/L, L1/L2, and W/L. Sixteen species of common freshwater fishes were sampled from a few localities in Peninsular Malaysia. Examinations were based on photographs to determine the scale morphologies. Basic distinguishable characteristics that were identified are type of scale, the overall shape, the position and shape of the focus, distribution of radii, and the circuli appearance. It was found that scale type and radii arrangement at the anterior field are two significant morphological features that could distinguish between and other families. Main characters used to identify scales at species level are radii cover, structure of inter radial tongue, and radii arrangement. Meanwhile, multiple comparison tests to reveal inter-specific variations suggested that there are significant differences among 16 species of common freshwater fishes studied. Two indices were found to be suitable to highlight the significant differences (P<0.05) for all species which are index L1/L2 and index W/L. For all indices, species that showed significantly different with most of other species are Osteochilus vittatus, Pristolepis fasciata, Rasbora sumatrana, and Labeo rohita. The scales of Osteochilus vittatus showed significant values with most of other species in more than one index; index L1/L and index L2/L. The distinctive morphological character that distinguished it from other Cyprinidae species is having clearly formed serrations in the middle of the inter-radial tongue at the anterior region.

Keywords: Fish scales, identification, morphological characters, inter-specific variations

INTRODUCTION

The conservation of biodiversity in aquatic environments especially in freshwater ecosystems puts fish as the main priority. To implement fish conservation, identification of fish at species level must be done [1]. Several methods have been recognized to identify fish species. Just like any other vertebrates, identification of fish species is normally done based on descriptions of the fishes’ external morphology and meristic characteristics [2-4]. Another identification method is via molecular technique which is by analyzing the DNA content of the specimens. However, there is one identification method that is not widely studied; that one by using their remains which are bones and scales. The focus of this study is on scales. Fish scales are easy to distinguish, non-destructive and undigested by mammals’ digestive system [5] and because of that, they can be very useful to provide taxonomic information which can be used to distinguish different species [6]. Scale morphologies can also be used to determine the age of the fish [7-10], the sexes of the fish [11], and the pollution status of the water body based on the size of the scales of the same fish [10] [12- 14]. This study is significant as one of conservation efforts for freshwater fishes. Those which are not capable to survive in polluted environments would leave their remains, such as scales. By acquiring knowledge of scale morphological structures, it is not impossible to identify which species lacking ability to adapt in such conditions. This study is also important in conserving fish predators such as otters by providing information on the diets and food preference of the predators based on examination of the predators’ faecal samples. Therefore, the conservation of biodiversity expands from preys (fishes) to their predators (other vertebrates) and the whole ecosystem eventually. Objectives of this study are to identify common freshwater fishes in Peninsular Malaysia up to species level by using the scales and to reveal inter-specific variations of scales between species by using specific indices developed from scale morphology.

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MATERIALS AND METHODS

Fishes were collected from rivers, swamps, ponds, lakes, irrigation canals and rice fields in Peninsular Malaysia. Sampling locations are Kuala Gula and Kampar (Perak), Bangi, Kuala Selangor and Tanjung Karang (Selangor), Jeli and Kuala Krai (Kelantan), and Temerloh (Pahang). They were then sorted, grouped, and identified based on their external features as provided from keys described by [15], before transported back to laboratory for scale removal. A total of 134 adult represented by 16 species which are Trichopodus pectoralis (Snakeskin Gouramy), Channa striata (Common Snakehead), Chelon macrolepis (Large-scale Mullet), Barbonymus gonionotus (Java Barb), Barbonymus schwanenfeldii (Tinfoil Barb), Osteochilus vittatus (Bonylip Barb), Pristolepis fasciata (Malayan Leaffish), Hampala macrolepidota (Hampala Barb), Rasbora sumatrana (Sumatran Rasbora), Barbodes binotatus (Spotted Barb), Anabas testudineus (Climbing Perch), Oreochromis mossambicus (Mozambique Tilapia), Cyprinus carpio (Common Carp), Labeo rohita (Roho Labeo), Hypsibarbus wetmorei (Lemon-fin Barb), and apogon (Beardless Barb) were examined. Scales were gently removed by using forceps. From each individual, only one scale was removed which was located below the lateral line and paralleled with the middle of dorsal fin from the left side of the body. Care was taken so that specimens were not damaged when removing adhered tissues from the scale. They were then soaked in 10% hydrogen peroxide for 30 minutes before rinsed in tap water and finally mounted. Images of scales were taken using a Canon 14-megapixels digital camera with black background served as contrast effect. Digital images were rendered by using Adobe Photoshop software. Based on the images taken, type of scale, the overall shape, the position and shape of the focus, distribution of radii, and the circuli appearance were identified. From the basic morphological characters described, primary and secondary characters were determined to distinguish between families and later to differentiate between species. The listed morphological descriptions were then used to construct keys to families and species. Measurements of scales were taken by using Image J software. The parameters of measurement involved are scale length (L), scale width (W), rostral field length (L1), and caudal field length (L2). Based on those measurements, four indices were formed which are relative to length (L); L1/L, L2/L, L1/L2 and L/W. The mean values of those indices were analysed by using post-hoc test to reveal inter-specific variations between species. The significant values indicated that the scale of a particular species is significantly different from another.

(a) (b)

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(c)

FIGURE 1. (a) Selected scale below the lateral line; (b) Characters for morphological descriptions; (c) Measurement for analysis of morphometric indices (L: Length; W: Width; L1: Length from anterior / rostral end to focus; L2: Length from focus to posterior / caudal end)

RESULTS AND DISCUSSION

There are seven families altogether and Cyprinidae is the family with the most number of species (10 species). Anabantidae, Channidae, Cichlidae, Nandidae, Osphronemidae, and Mugilidae, are each represented by a single species. Since the majority of species belongs to Cyprinidae, key to families were constructed to distinguish Cyprinidae from other families. Besides the known basic characters, radii arrangement, gaps formed between radii, and distinctiveness of radii formation are additional morphological characters that are important to distinguish among families and species. The primary characters observed for identification up to the family level are type of scale and radii arrangement, specifically at the anterior field. The secondary characters are overall scale shape, gaps formed between radii, and distinctiveness of radii formation at the anterior margin. There are only two types of scales; ctenoid and cycloid. Ctenoid scales are easily differentiated due to the clear presence of ctenii at the posterior or caudal end of the scale. Cycloid type on the other hand, besides lacking ctenii, is described as disc-shaped, smooth, and thin scale. All species belonging to Cyprinidae are cycloid type. Species of Channidae, Cichlidae, and Mugilidae also belong to cycloid type. Only species of Anabantidae, Nandidae, and Osphronemidae are ctenoid type. Radii of Cyprinidae appear in various forms. They could be found arranged in all fields; anterior, lateral, and posterior fields; closely arranged and numerous, or having huge gaps between them. Unlike Cyprinidae, other families appear to have radii, which are distinctively arranged at the anterior field. For the species level, the primary characters used are radii cover, structure of inter radial tongue, and radii arrangement, while the secondary character is the focus appearance. Variety of overall scale shape was observed in and between species. Only two species showed consistency of scale shape in every specimen examined, namely Oreochromis mossambicus and Pristolepis fasciata. Both species have rectangular-shaped scales. Details of morphological characters for all 16 species are tabulated in Table 1, followed by key to families and key to species in Table 2 and Table 3, respectively.

(a) (b) (c)

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(d) (e)

FIGURE 2. (a): Ctenoid type; (b): Cycloid type; (c): Radii of Barbodes binotatus (Spotted barb) cover the anterior, lateral, and posterior fields; (d): Scale of Pristolepis fasciata (Malayan Leaffish) showing rectangular overall shape; (e): Scale of Osteochilus vittatus (Bonylip Barb) having clearly serrated formation of inter-radial tongue in the middle of the anterior margin

TABLE 1. Important morphological characters discovered for scales of sixteen common freshwater fishes in Peninsular Malaysia. Primary characters Secondary characters Species Type of Radii cover Radii Inter radial Focus scale arrangement tongue position structure Barbodes binotatus Cycloid Anterior, posterior, Uniform, Irregular, In the lateral distinct serrated middle Barbonymus gonionotus Cycloid Anterior Uniform, Uniform, In the distinct serrated middle Barbonymus Cycloid Anterior Uniform, Uniform, Towards schwanenfeldii distinct serrated anterior Cyclocheilichthys Cycloid Anterior and Not uniform, Uniform, In the apogon posterior numerous curvy middle Cyprinus carpio Cycloid Anterior and Not uniform, Irregular, not In the posterior numerous serrated middle Hampala macrolepidota Cycloid Anterior, posterior, Uniform, Irregular, In the lateral distinct serrated middle Hypsibarbus wetmorei Cycloid Anterior Uniform, Uniform, In the distinct curvy middle Labeo rohita Cycloid Anterior, posterior, Not uniform, Irregular, not In the lateral numerous serrated middle Osteochilus vittatus Cycloid Anterior and Uniform, Uniform, Towards posterior distinct serrated anterior Rasbora sumatrana Cycloid Anterior and Not uniform, Irregular, In the posterior distinct serrated middle Anabas testudineus Ctenoid Anterior Uniform, Uniform, In the distinct serrated middle Channa striata Cycloid Anterior Uniform, Uniform, Towards distinct serrated posterior Oreochromis Cycloid Anterior Uniform, Uniform, In the mossambicus distinct serrated middle Pristolepis fasciata Ctenoid Anterior Uniform, Uniform, Towards distinct serrated posterior Trichopodus pectoralis Ctenoid Anterior Uniform, Uniform, Towards distinct serrated posterior Chelon macrolepis Cycloid Anterior Uniform, Uniform, Towards distinct serrated posterior

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TABLE 2. Key to families 1. Type of scale is cycloid...... 2 1. Type of scale is ctenoid...... 5 2. Radii are not distinctively arranged at the anterior field...... Cyprinidae 2. Radii are distinctively arranged at the anterior field...... 3 3. Overall scale shape is rectangular...... Cichlidae (Oreochromis mossambicus) 3. Overall scale shape is not rectangular...... 4 4. Gap between radii is very small...... Channidae (Channa striata) 4. Gap between radii is moderate...... Mugilidae (Chelon macrolepis) 5. Radii is distinctively formed at the anterior margin...... Anabantidae (Anabas testudienus) 5. Radii is not distinctively formed at the anterior margin...... 6 6. Overall scale shape is rectangular...... Nandidae (Pristolepis fasciata) 6. Overall scale shape is square...... Osphronemidae (Trichopodus pectoralis)

TABLE 3. Key to species (Cyprinidae) 1. Radii cover the anterior, posterior, and lateral fields...... 2 1. Radii do not cover the anterior, posterior, and lateral fields...... 3 2. Inter radial tongue is more serrated...... Barbodes binotatus 2. Inter radial tongue is less serrated...... Hampala macrolepidota 3. Radii cover anterior and posterior fields...... 4 3. Radii do not cover anterior and posterior fields...... 8 4. Radii are closely arranged and numerous...... 5 4. Radii are not closely arranged and not numerous...... 7 5. Numerous secondary radii formed at lateral field...... Labeo rohita 5. Secondary radii not formed at lateral field...... 6 6. Inter radial tongue is curvy...... Cyclocheilichthys apogon 6. Inter radial tongue is a horizontal line...... Cyprinus carpio 7. Serrations clearly formed in the middle of the anterior tongue...... Osteochilus vittatus 7. Serrations not formed in the middle of the anterior tongue...... Rasbora sumatrana 8. Gaps between radii are huge...... Hypsibarbus wetmorei 8. Gaps between radii are moderate...... 9 9. Position of focus is towards anterior...... Barbonymus schwanenfeldii 9. Position of focus is in the middle...... Barbonymus gonionotus

Based on the analysis of morphometric indices; L1/L, L2/L, L1/L2 and W/L, there are inter-specific variations among 16 species of common freshwater fishes studied. Analysis of the post-hoc test shows that index L1/L2 and index W/L were found to be suitable to highlight the inter-specific variations for all species. All 16 species show significant differences (P<0.05) between species from both indices. For index L1/L, all except Barbonymus schwanenfeldii show significant differences while for index L2/L, all except B. schwanenfeldii and Hypsibarbus wetmorei show significant differences among species. For all indices; L1/L, L2/L, L1/L2 and W/L, species that showed significantly different with most of other species are Osteochilus vittatus (9 species), Pristolepis fasciata and Osteochilus vittatus (8 species each), Rasbora sumatrana (9 species), and Labeo rohita (14 species), respectively. The values of Osteochilus vittatus show significance difference with most of other species in more than one index; index L1/L and index L2/L. The shape of this scale varies from rectangular to round. The focus forms a single dot, concentric, and heads towards anterior. The distinctive morphological character that distinguished it from other Cyprinidae species is having clearly formed serrations in the middle of the inter-radial tongue at the anterior region. It is important to note that the keys to family or species identification are only applicable to these 16 common freshwater fishes in Peninsular Malaysia. Therefore, further studies are needed to describe more morphological characters of other species so that hidden, minute characters of scales can be revealed, in an effort of completing the keys. Nevertheless, the keys developed in this study are significant and can act as guidelines for future studies. It is hoped that identification of common fish species based on scale morphologies would be helpful for conservation purposes.

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ACKNOWLEDGEMENTS

The authors wish to thank Dr. Pazil Abdul Patah from the Department of Wildlife and National Park (DWNP), who conducted the study of otters’ feeding behaviour by observing fish scales obtained from otters’ stomach contents and faecal samples, for his consistent guide and support. We also would like to thank other colleagues; Nur Syuhada Nazron, Mohd Sanusi Mohamed, Mohd Faiq Hamdan, Mohd Zairi, and Norsham who provided technical supports during fieldworks of this study.

REFERENCES

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