MORPHOMETRIC AND MERISTIC CHARACTERISTICS OF WALKING SNAKEHEAD CHANNA ORIENTALIS IN A WETLAND ECOSYSTEM (NORTHWESTERN BANGLADESH) USING MULTI-LINEAR DIMENSIONS

The present study is illustrated complete morphometric and meristic characteristics of fresh water fish, walking snakehead, Channa orientalis (Bloch & Schneider 1801), using nine linear dimensions and covering different fin-rays (i.e., dorsal fin, D; pectoral fin, P1; pelvic fin, P2; anal fin, A and caudal fin,C) from the wetland ecosystem Gajnar Beel in northwestern (NW) Bangladesh. Total 230 specimens of C. orientalis were collected from the Gajnar Beel in the time of January to December 2018 by several local fishing gears (e.g., cast net, gill net and square lift net (mesh size ranges: 1.5 2.5 cm, 1.5 2.0 cm, & ~2.0 cm, respectively). Different morphometric lengths were measured to 0.01 cm, and whole body weight (BW) was estimated 0.01 g for each individual. Fin rays and scales (including lateral line scale) were computed by a magnifying glass. All LWRs were highly significant (p<0.0001) with the r2 values ≥0.978. Based on r2 value, LWR by BW vs. TL was the best fitted model among nine equations. However, the LLRs were also significant with r2 values ≥0.992. According to r2 value, LLR by TL vs. SL (TL = a + b × SL) shown the best fitted model among eight equations. The fin formula of C. orientalis is: dorsal: D. 29-35; Pectoral, P1. 12-14; Pelvic, P2. 5-6; Anal, A. 20-22; Caudal, C. 12-14. A double lateral line is present which continued with 12-13 scales in the first line and 26-28 scales in other line. The present study will be helpful for the species identification and resource management of C. orientalis in the Gajner Beel NW Bangladesh and other sub-tropical countries.


Introduction
The walking snakehead, Channa orientalis (Bloch and Schneider 1801) is a freshwater widely adapted species belonging to the family of Channidae under the order of Perciformes (Rahman 1989). It is known as Cheng or ghachua in Bangladesh; Chengal, Cheng in India; Nga-yan-goungdo, in Myanmar; Brown snakehead, Smooth-breasted snakehead in Sri Lanka, Chenga, Garahi in Nepal. C. orientalis is well-known in Indian subcontinent and surrounding areas ranging across Afghanistan, Bangladesh, India, Myanmar, Nepal, Pakistan and Sri Lanka. This species is an economically essential target and most favored aquarium fish species through Asian countries (Froese and Pauly 2019). C. orientalis is piscivorous, carnivorous species and easily attracted by any moving baits (Rahman 1989). C. orientalis are found in freshwater environment including rivers, lakes, ponds, mountain streams and even brackish water (Rainboth 1996). This species has a high market price and also has huge survival in adverse situation. This species is vulnerable through worldwide (IUCN 2019) and as of least concern in Bangladesh (IUCN 2015). The term 'morphometric' can be defined as a technique for describing body form by measuring the length or distance between physical features or landmarks (Muchlisin 2013). On the other hand, meristic is an area of ichthyology which relates to counting quantitative feature of fish, such as the number of fins or scales. Morphometric and meristic counts are very useful for the species identification, sex determination and classification of any fish species in a laboratory or in the fields (Bagenal and Tesch 1978, Dynes et al. 1999, Jayaram 1999, Nawer et al. 2017, Rahman et al. 2019. So, studies on morphometric and meristic features can be constructive tools for exact identification of any species and its classification (Bagenal and Tesch 1978, Hossen et al. 2016, Islam et al. 2020. Moreover, in fisheries research, appraising the well-being of individuals as well as evaluating the life history and the morphological traits of populations of different locality greatly relies on morphometric characters (King 2007, Hossain 2010, Hossain et al. 2013). There are very few works have been done on length-weight relationships and morphometric and meristic variation in fins of C. orientalis (Charjan and Kulkarni 2014, Sharma et al. 2015, Hossain et al. 2017a). However, no profound studies have been conducted on this species yet from the Gajner Beel and elsewhere. Details and perfect information on morphometric and meristic characters of C. orientalis is really needed for the proper management. So, this study will provide the first complete and informative description on morphometric characters, length-weight relationships (LWRs), length-length relationships (LLRs) and meristic characters of C. orientalis from the Gajner Beel in NW Bangladesh using multi-linear dimensions.

Fish sampling
This study was continued in Gajner Beel, northwestern Bangladesh (23°54′ N; 89°52′ E) from January to December 2018. A total of 230 individuals of C. orientalis were collected through various types of traditional fishing gears including Cast net, Gill net and Square lift net (mesh size ranges: 1.5 -2.5 cm, 1.5 -2.0 cm, & ~2.0 cm, respectively). At sampling site samples were chilled by ice in the ice box and after reaching in the laboratory samples were preserved with 10% buffered formalin.

Meristic counts
The meristic counts of fin rays of C. orientalis in various body parts like dorsal, pectoral, pelvic and caudal fins was detected by a magnifying glass with zoom range 4x.

Growth pattern
The relationships of morphometric between body weight and lengths were calculated as W= a × L b , where 'W' means the body weight (g) and 'L' means the various lengths (e.g., Total length, TL; standard length, SL etc.) in cm. a and b known as regression parameters, calculated through linear regression analyses which depends on natural logarithms: ln (W) = ln (a) + b ln (L). Here, 95% confidence limit (CL) of a and b and the co-efficient of determination (r 2 ) were also calculated from this way of analyses. In this study, analysis of LLRs was done by linear regression analysis. The best model for both LWRs and LLRs was determined by the highest r 2 value.

Statistical analyses
GraphPad Prism 6.5 software was used for statistical analyses of correlation with the consideration of 5% (p<0.05) significant level.

Results
The body shape of C. orientalis is elongated, fairly rounded in cross-section. Mouth is large with villi form teeth on jaws. Eyes are moderate, its diameter 5 to 6 times in head length. Pectoral fin is extending to anal fin and pelvic fin about 50% of pectoral fin length. Caudal fin is rounded. Large plate-like scale is on head. Body colour is black to light green on dorsal side and white to pale on ventral side with a faint bluish or reddish tinge. Pectoral fin with a series of distinct alternating blue and pale orange vertical bands; outer margins of the dorsal, caudal and anal fins are slate-coloured with scarlet and barred strips (Fig. 2). In this study, TL was varied from 7.9-18.5 cm (Mean±SD = 13.82±2.47) and BW was diverse from 4.61-70.72 g (32.03 ±16.42) ( Table 1). Regression parameters a and b with 95% confidence intervals and coefficients of determination (r 2 ) for LWRs of C. orientalis are shown in Table 2. All LWRs were highly significant (p<0.0001) with r 2 values ≥0.978. Based on r 2 value, LWRs by BW vs. TL was the best fitted model among nine equations. The LLRs are shown in Table 3 and all relationships were also highly correlated (p<0.0001) with r 2 values ≥0.992. On the basis of maximum r 2 value, LLRs by TL vs. SL was the best fitted model among eight equations. Furthermore, the fin formula presents only soft fin rays and their number varies. In our study, the fin formula was D. 29-35; P1. 12-14; P2.5-6; A. 20-22; C. 12-14 (Fig. 3). A double lateral line is present which continued with 12-13 scales in the first line and 26-28 scales in other line.

Discussion
Information on the morphometric and meristic traits are quite insufficient for C. orientalis in Gajner Beel, NW Bangladesh though a very few works have been done on morphometric and meristic traits of C. orientalis worldwide. So, this is the first complete and informative work on morphometric and meristic characters of C. orientalis in the Gajner Beel. During this study, absence of C. orientalis smaller than 7.9 cm TL may be assigned for the selectivity of the fishing gear or fishermen did not go there where fish species were larger sizes, or the species did not go up with larger sizes in the wetland ecosystem. During this study, the maximum length was 18.5 cm TL, that is quite similar with previous study in Gajner Beel (18.4 cm TL) (Hossain et al. 2017a) and also similar with the findings observed in Ravi River, India (19.0 cm TL) (Sharma et al. 2015). Maximum length is beneficial to calculate the growth parameters (i.e., asymptotic length, growth coefficient), thereby essential for resource management for fisheries (Hossain et al. 2017a).
The allometric co-efficient (b) values of LWRs may vary between 2.0 and 4.0 (Carlander 1969) and the allometric co-efficient (b) values of LWRs also ranging from 2.5 to 3.5 are more common (Froese 2006). In our study, the allometric co-efficient, b value was 3.17 which indicated as allometric growth pattern. The b values of LWRs ranging from 2.5 to 3.5 are more general (Islam et al. 2021) and our value is within the range. In general b values close to 3, indicate that fish grow isometrically and it different from 3.0 indicate allometric growth (>3 positive allometry and <3 negative allometry) (Tesch 1971). So, our present study shows b values greater than 3 which indicates positive allometric growth pattern. Some previous research had been reported the b value as 3.17 (Hossain et al. 2017a) and 3.01 at Gajner Beel northwestern Bangladesh and at Ravi River, India respectively (Sharma et al. 2015).
The observed b value will be effective for future research especially in this habitat or other. However, the b values may divers in the same species because of the assemblage of several factors including habitat, variations of growth in different body parts, stage of stomach fullness, sex, seasonal effect, physiology, gonadal maturation, preservation methods and differences in the observed length ranges of the specimens collected which were not accounted during the present study (Tesch 1971, Hossain et al. 2015, Hossain et al. 2017b, Hossain et al. 2018. Besides, all of LLRs were shown highly correlated (p <0.0001). In this study, the observed fin formula was dorsal fin, D. 29-35; pectoral fin, P1. 12-14; pelvic fin, P2. 5-6; anal, A. 20-22; and caudal fin, C.12-14 which was similar with the earlier studies (Rahman 1989, Talwar andJhingran 1991). This study shows that different fins are presented in pictorial format separately which can be very effective for future research in this habitat or other.

Conclusion
This study highlights the baseline of biological information which should be helpful for the development of management strategies in relation to the fishery. It would also be helpful for the conservation of C. orientalis population in Gajner Beel, a wetland ecosystem and the neighboring ecosystems.