Truss Morphometric and Meristic Characters of Male and Female Donkey Croaker (Pennahia anea (Bloch 1793)) Taken from Asemdoyong Auction Center Pemalang, Central Java

Keyword: Donkey croaker Sexuality Meristic Morphometric Pennahia anea is among of the demersal fish landed at Asemdoyong Fish Auction Centre, Pemalang. P. anea doesn't show sexual dimorphism, so that other characters are needed to differentiate male and female individuals, i.e. truss morphometric and meristic characters. Previous studies have shown that truss morphometric and meristic can differentiate between male and female individuals. This study aims to describe the morphometric and meristic truss characters and determine the truss morphometrically and meristic characters that distinguish between males and females of Pennahia anea. The research used a survey method with a purposive random sampling technique. Male and female individuals of P. anea were examined based on their meristic and truss morphometric characters. The data were analyzed statistically using Mann Whitney non-parametric test. The result proved that male and female were significantly different in seven out of the 31 truss distances. Male individuals had a larger size than female individuals in three truss distances. In contrast, the male had a smaller size than the female individuals in four out of seven truss distances that distinguish both sexualities. The soft fin radius of the ventral fin was significantly different between male and female of P. anea. It could be concluded that male and female individuals of Pennahia anea have different truss distances and meristic characters with seven truss distances and one meristic character are different. Article history: Received: 06/06/2021 Revised: 15/07/2021 Accepted: 18/07/2021


Introduction
Indonesia is a maritime country with the second-longest coastline (108,000 km) (Peristiwady, 2019). Pemalang coastline is part of the Indonesia coastline that resides in the North of Central Java with approximately 35 km (Marcos, 2016;Waridin, 2007). This regency has five Fish Auction Centers (TPI), and the largest is TPI Asemdoyong (Karningsih et al., 2014;Rahmawati et al., 2013). Many fish species have been landed in Asemdoyongs' Fish Auction Center, one of which is Pennahia anea. Pennahia anea has a common name Donkey Croaker (Ernawati & Sumiono, 2010;WoRMS, 2021).
Donkey Croaker is distributed in tropical and subtropical regions and abundant in the Indian Ocean (Wagiyo et al., 2020). The maximum body size found in China, Thailand, the Philippines, Malaysia, and Indonesia was 300 mm (Ernawati, 2007). However, P. anea that live in the Indian and Pacific Oceans has a maximum body size of 400 mm (Tuuli et al., 2011). P. anea belongs to the demersal fish group (Baransano & Mangimbulude, 2011). This species lives in coastal waters with a depth of up to 60 meters and commonly found in muddy water (Wagiyo et al., 2020). P. anea has a high economic value. Its meat is consumed as a protein source, and the swim bladder is sold at a high price because of its good health benefits (Tuuli et al., 2011;Yulianto et al., 2016).
The morphological characters of P. anea are pointed snout, large mouth, and no barbells. It has two pairs of a tiny pore. The first pair of pores are in front of the chin, separated by symphysis. The upper teeth are larger than the lower teeth, do not have canine, the abdomen has a white colour, the caudal fin is truncate, and has 22-25 soft dorsal fins (White et al., 2013) P.anea is fish species that do not show sexual dimorphisms. In such case, male and female fish cannot be easily differentiated morphologically without specific technique. The only technique can be distinguished male and female individual is by observing their gonads through dissection (Rahardjo et al., 2011). However, that technique is not reliable for immature individuals, where gonads are not fully developed. According to Wijayanti et al. (2017), male and female immature fish individuals can be differentiated using truss morphometric and meristic characters. Therefore, this study tried to evaluate the possibility of using truss morphometric and meristic characters to distinguish male and female of P. anea.
Truss morphometric observes all distances between truss points on the body, then compared with standard lengths to obtain a constant value even though the observed fish size are varies (Onsoy et al., 2011). Meristic is a method of counting characters, which is done by counting certain body parts (Putri et al., 2015). Usually, the part of the body that calculated as the number of hard and soft rays on the dorsal, caudal, anal, ventral, pectoral fin, and the number of scales on the lateral line (Radona et al., 2017). Meristic characters can be affected by environmental factors such as water salinity, water temperature, and dissolved oxygen in the water, which affects the growth process of fish larvae, so there may be different characters when the fish are adults (Resmayeti, 1994). The previous study had proven the reliability of truss morphometric and meristic characters for distinguishing male or female fish individuals (Auliana et al., 2017). Auliana et al. (2017) found that the distance between the tip of the snout and the dorsal part of the border between head and body can distinguish male and female Tontobi fish (Nematalosa erebi). At the same time, the number of fin ray in the anal fin is also a distinguishing character (Soleh et al., 2010).
This study aimed to differentiate truss distances and meristic characters of male and female individuals of Donkey Croaker (Pennahia anea) and to determine the number of truss distances and meristic characters can distinguish male and female of Donkey Croaker (Pennahia anea).

Sampling site and times
We focused on Pennahia anea that landed in Asemdoyong Fish Auction Center Pemalang Central Java. According to the research focus, fish samples collected from fish seller at the auction centre ( Figure 1). The samples collected in April and May 2020.

Fish handling and identification
A total of 30 individuals consisted of 15 individuals of male and female Pennahia anea were examined during the study. Fresh individual fish samples were placed in cooler boxes to keep their morphological performances and colour. Upon arrival in the laboratory, the specimens were put in a freezer at -20°C until further examination. Trus morphometrics characters, standard and head length, were measured using a calliper with an accuracy of 0.005 cm (Affandi et al., 1992). Truss morphometric measurements were conducted between 16 benchmark points and 31 truss distances ( Figure 2). The truss distances were summarized in Table 1. The meristic characters were the number of gill rakers, the number of hard and soft rays on the dorsal, caudal, anal, ventral, and pectoral fins, the number of scales on the lateral line, the number of scale above the lateral line, and the number of scale under the lateral line. A total of 16 meristic characters were compared between male and female individuals (Sukmaningrum, Suryaningsih, & Nurhaeni, 2020), with slight modification on the number of benchmark points and truss distances.
Conventional identification was performed to ensure the taxonomic status of the samples. Identification was following the identification book from (Carpenter & Niem, 2001;Saanin, 1984;White et al., 2013). The validity of obtained scientific names was referred to the database available in FishBase (Froese & Pauly, 2018). Phylogenetic analysis was performed through phylogenetic tree or cladogram reconstruction. The cladogram was reconstructed based on 24 morphological characters, divided into three groups of characters; the ratio between two morphometrics measure, meristic, and general morphology performance. Morphometric characters refer to Dulčić (2005). Detail characters used for phylogenetic analysis summarized in Table 1.

Data analysis
Data of truss distance and meristic characters, compared with the standard length, were analyzed using the "Mann-Whitney" test using SPSS software to distinguish male and female fish. The test was based on a 95% significance level or asymptote significance value of 0.05. The sexuality of the fish specimens was determined through dissection. Fish was dissected from the beginning anus to the anterior part of the stomach until to behind the operculum and dissected to the ventral part using surgical scissors. Dissection was performed carefully so as not to damage the internal organs, especially the gonads. The gonad topography was observed compared to the gonad topography of fish in (Sukamto et al., 2010).

Results and Discussion
The total number of individuals fish samples used in this research was 53. The total length of fish samples ranges from 11.33 to 20.25 cm, while the weight (Carpenter & Niem, 2001), P. anea can grow up to 30 cm in length. According to Carpenter and Niem (2001) and White et al. (2013), Fish sample identification was conducted. It was proved that all the collected fish from TPI Asemdoyong belong to P. anea.
The morphological character of fish samples was fusiform with lateral line scales reaching the caudal fin's hind margin (Carpenter & Niem, 2001). The body colour was silvery grey, with the tip of the dorsal fin blackish. The observed colour is following White et al. (2013), who stated that P. anea has a fusiform body shape, with silvery grey body colour. According to Carpenter and Niem (2001), P. anea has a grey head and body. The abdomen is paler with silvery reflection.  (2-14) The distance between the tip of the snout and The prominent part of the head The distance between the border between head and body (ventral part) and The border between head and body (dorsal region) 6 A6 (4-1) The distance between the border between head and body (dorsal part) and The base point of the lower jaw 7 A7 (4-14) The distance between the border between head and body (dorsal part) and The prominent part of the head  The distance between the back base of the 2nd dorsal fin and The front bottom of the anal fin 22 C10 (11-12) The distance between the back base of the ventral fin and The midway between the ventral and anal fin 23 C11 (12-7) The distance between the midway between the ventral and anal fin and The front base of the anal fin The shape of the caudal fin is truncated (Figure 4.2. (a)). The type of scale is ctenoid (Figure 4.2. (b)), but there are cycloid scales on the head (Figure 4.2. (c)). The mouth position is terminal (Figure 4.2. (d)) and has small teeth on the lower jaw and large teeth without large fangs in the upper jaw (Figure 4.2. (e)). The observed characters follow Carpenter and Niem (2001) statement that P. anea has cycloid scales on its head, and in other parts, it has ctenoid scales. White et al. (2013) stated that this species has large upper teeth without large canines. Other morphological characters that distinguish P. anea from different species don't have a barbell and have two pairs of mental pores (Puspasari et al., 2020) (Figure 4.2. (e)). According to Carpenter and Niem (2001), these two pairs of mental pores are small. Based on Sasaki (2001) and Zhu et al. (1975) Sciaenidae generally has pores at the tip of the snout and lower jaw.
Observation of gonads in P. anea showed that male gonad was elongated, milky white, and a pair. The female gonad was elongated, yellowish to orange, and the number was a pair (Figure 3). Both male and female gonads are located under the swim bladder. The characters follow Burhanuddin (2008) statement that the fish gonads are a pair, with the colour and size according to the level of maturity of the gonads.
The gonads are elongated, located laterally or ventrally to the swim bladder. The male gonads (testes) are whitish, while the female gonads (ovaries) are reddish-yellow.
The results of measuring the ratio between the truss distance and the standard length and tested using the "Mann Whitney" are presented in Table 2. It is summarized in Table 2 there were 7 out of 31 characters that the Asymptote Significance value less than 0.05. It was clear that the ratio of the truss distance that distinguishes male and female P. anea are A1, A3, B4, C8, C9, D3, and D5 ( Figure 4). Based on Tuuli et al. (2011), P. anea is a gonochoric. Gonochoris is each individual has one genital (male or female). Tuuli et al. (2011) stated that the minimum size of gonad maturity for female P. anea was 125 mm in standard length, whereas, for males, it was 119 mm.  The A1 character is the distance between the base points of the lower jaw and the tip of the snout. In male fish, the value was 19.23. In female fish, the value was 32.53. The A3 character is the distance between the tip of the snout and the ventral part of the border between head and body. In males, the value was 21.77. In female fish, the value was 30.71. The B4 character is the distance between the front base of the 1st dorsal fin and the ventral part of the border between head and body. In males, the value was 21.91. In female fish, the value was 30.61. It was observed that the male individual has a shorter distance than the female individual for those three truss characters (Tjahjo & Purnamaningtyas, 2008). In contrast, the male individual has a longer truss distance than the female individual for C8, C9, D3, and D5 truss characters. The C8 character is the distance between the back base of the 2nd dorsal fin and the midway between the ventral and anal fin. In males, the value was 32.68. In female fish, the value was 22.97. The C9 character is the distance between the back base of the 2nd dorsal fin and the front bottom of the anal fin. In males, the value was 33.73. In the female, the value was 22.23. The D3 character is the distance between the dorsal folds of the tail and the front base of the anal fin. In the male, the value was 32.59. In the female, the value was 23.03. The D5 is the distance between the front base of the anal fin and the back base of the anal fin. In males, the value was 32.68. In the female, the value was 22.97. From the results of data analysis, it was found that female P. anea has a longer anterior body, while male P. anea has a longer posterior body.
A similar study by Asiah et al. (2019), Sukmaningrum, Suryaningsih, and Sari (2020) found that the truss morphometric characters that differentiate male and female Oxeye Scad (Selar boops) were B1, B4, B9, D2, and D5. The B1 character is the ratio of the truss distance between the dorsal part of the border between head and body and the base of the anal fin. The B4 character is the ratio of the truss distance between the dorsal part of the border between head and body and the bottom of the anal fin. The B9 character is the truss distance between the front base of the 1st dorsal fin and the front base of the anal fin. The D2 character is the ratio of the truss distance between the back base of the anal fin and the dorsal fold of the tail. It was observed that the male individual has a shorter length than the female individual for those four characters. In contrast with the D5 character, the male individual has a longer distance than the female individual. The D5 character is the ratio of the truss distance between the ventral fold of the tail and the dorsal fold of the tail.
The result of the calculation of meristic characters is presented in Table 3 From these results, it is known that P. anea has fin formula D1.VIII-10; D2.I.22-25; C.17-20; A.II.7-8; V.I.4-5; P.14-17. The number of scales on the lateral line was 50 to 53. The number of scales above the lateral line was 6 to 8. The number of scales below the lateral line was 12 to 15. Carpenter and Niem (2001) P. anea has 9 to 10 hard fin rays on the 1st dorsal fin and one hard ray on the 2nd dorsal fin with 22 to 24 soft rays. The anal fin has two hard rays and seven soft rays.  (Sukmaningrum, Suryaningsih, & Nurhaeni, 2020;Sukmaningrum, Suryaningsih, & Sari, 2020;Suryaningsih et al., 2019;Wijayanti et al., 2017). Wijayanti et al. (2017) proved that truss morphometric characters could differentiate male and female bigeye ilisha (Ilisha megaloptera). Similar result was also reported by Sukmaningrum, Suryaningsih, and Nurhaeni (2020) in Splendid threadfin (Philimanus perplexa Feltes, 1991), Sukmaningrum, Suryaningsih, and Sari (2020) in selar bengol (Selar boops); and Suryaningsih et al. (2019) in silver barb Fish (Barbonymus gonionotus Bleeker, 1849). Based on present and those previous studies, it seem that truss morphometric is a reliable technique to differentiate male and female individuals of streamline body form fish although they do not show sexual dimorphisms.
Information on male and female individuals of Pennahia anea is vital for breeding program in domestication or mariculture development of this species (Badrudin et al., 2011;Hegde et al., 2016). Information of male and female Pennahia anea is also essential for estimating population dynamic in natural populations which finally important for sustainable harvest of Pennahia anea (Lavictory et al., 2016;Suman et al., 2016).

Conclusion
Based on the result and discussion, it can be concluded that male and female individuals of Pennahia anea have different truss distances and meristic characters. Seven truss distances and one meristic character can distinguish male and female individuals of Pennahia anea. In the future studies, additional fish samples and truss distances are needed to improve the reliability of the method.