JJBS Volume 14, Number 1, March 2021 ISSN 1995-6673 Pages 129 - 135 Jordan Journal of Biological Sciences Life History Traits of the Gangetic scissortail rasbora, Rasbora rasbora (Hamilton, 1822) in the Payra River, Southern Bangladesh Newton Saha1,*, Mohaiminul Haque Rakib2, Md. Mahamudul Hasan Mredul3, Md. Arifur Rahman4 and Ferdous Ahamed1 1 Department of Fisheries Management, Patuakhali Science and Technology University, Dumki, Patuakhali-8602, Bangladesh,2Faculty of Fisheries, Patuakhali Science and Technology University, Patuakhali, Bangladesh,3Department of Aquaculture, Patuakhali Science and Technology University, Dumki, Patuakhali-8602, Bangladesh,4Department of Fisheries Biology and Genetics, Patuakhali Science and Technology University, Dumki, Patuakhali-8602, Bangladesh Received Feb 16, 2020; Revised July 25, 2020; Accepted July 25, 2020 Abstract The near threatened gangetic scissortail rasbora, Rasbora rasbora (Hamilton, 1822), is an economically important, and nutritionally valuable freshwater food fish in south Asian countries. The present study provides the first inclusive explanation on life-history traits of R. rasbora in the Payra River, southern Bangladesh. This species invites research interest due to its nutritional demand and IUCN red list status. Sampling was carried out using different traditional fishing gears during July to December 2019. For each individual, total length (TL) and standard length (SL) were measured to the nearest 0.01 cm using digital slide caliper, while body weight (BW) was taken by an electronic balance with 0.01 g accuracy. A total of 215 specimens were measured ranging from 2.6-12.5 cm TL and 0.22- 10.65 g BW during this study. The 4.00 to 4.99 cm TL was numerically leading group of the total population. The allometric coefficient (b) of the length-weight relationships (LWRs) indicates negative allometric growth pattern (b<3.00) for R. rasbora in the Payra River. The results also indicate that the LWRs were highly significant (p<0.001) with r2 values >0.963. In addition, The LLR (SL vs. TL) was highly significant (p<0.0001) with a coefficient of determination values of 0.988. The estimated form factor (a 3.0 ) was 0.007 indicating this fish is elongated in body shape and the size at first sexual maturity (L m ) for combined sexes of R. rasbora was calculated as 7.96 (~8.00) cm TL in the Payra River. The allometric condition factor (K A ) varied from 0.0063 to 0.0570 and Fulton′s condition factor (K F ) varied from 0.3933 to 4.1844. However, K F tended to be lower after 9.0 cm for combined sexes, which may indicate the start of sexual maturation and therefore L m could be around 8.0 cm TL for R. rasbora. The knowledge about the biological aspects of gangetic scissortail rasbora may be used for improved management tools in the future. . Keywords: Rasbora rasbora, Growth pattern, Conditions, Size at first sexual maturity, Payra River 1. Introduction Cyprinidae is the largest and most diverse fish family and the largest vertebrate animal family in general, with about 3,000 species of which only 1,270 remain extant, divided into about 370 genera (Froese and Pauly, 2015). The family belongs to the ostariophysian order Cypriniformes, of whose genera and species the cyprinids make up more than two-thirds. Rasbora rasbora (Hamilton, 1822) is a member of family Cyprinidae commonly known as Gangetic scissortail rasbora. Apparently, it is native to Bangladesh, India (Gangetic provinces and Assam), Myanmar, Pakistan and Thailand (Talwar and Jhingran, 1991). It is a surface feeder fish (IUCN Bangladesh, 2015). In Bangladesh, R. rasbora is commonly known as darkina/leuzzadarkina of the important small indigenous fish (SIS) species. Being a small indigenous fish species, R. rasbora is well-regarded as a quality food containing high amount protein, fat, carbohydrate, calcium and vitamins that helps to eliminate * Corresponding author e-mail: newtonsaha@pstu.ac.bd. malnutrition, particularly for poor women and children in Bangladesh (Thilsted et al., 1997; Ross et al., 2003). In addition, it can also be used as an aquarium fish (Froese and Pauly, 2015). The large numbers of small fish species are still available in southern water bodies amongst them, R. rasbora locally known as darkina/ kan chela is one of important ones. The Payra River (southern Bangladesh) is considered as an important natural spawning and nursery grounds for many commercially important fish species and a significant portion of the country’s fisheries production is dependent on this coastal river (Islam et al., 2015). Nonetheless, the untamed population of this species is waning due to overfishing, reckless fishing of larvae and juveniles, habitat destruction (siltation), pollution and other ecological changes to their surroundings (Islam et al., 2015; Hossen et al., 2015; Hossain et al., 2016, 2015) and afterward categorized as near threatened in Bangladesh (IUCN Bangladesh, 2015) although globally categorized as least concern (IUCN, 2019). Hence, there is an urgent need to manage and regulate its numerous 130 © 2021 Jordan Journal of Biological Sciences. All rights reserved - Volume 14, Number 1 discrete stocks, which will require basic population dynamics information for the species (Santos et al., 1995). Usually, studies of length-frequency distribution (LFD) express the life-history traits and ecology of fishes (Ranjan et al., 2005). In addition, length-weight relationships (LWRs) are considered as a useful tool in fisheries studies for the estimation of weight, biomass, and condition indices (Anderson and Gutreuter, 1983; Froese, 2006; Froese et al., 2019). Moreover, condition factors assist evaluate the status of fish from which the present and future population success can be predetermined (Richter, 2007; Rypel and Richter, 2008). This is believed to be the first report on biological aspects of this population in this region. However, sufficient information on this species is still now absent in the literature from Bangladeshi waters or elsewhere which attracted our attention. Therefore, the current study provides a complete and informative depiction of the life history traits of R. rasbora – including LFD, LWRs, LLR, form factor (a 3.0 ), size at first sexual maturity (L m ) and condition factors (allomatric, K A ; Fulton’s, K F ; relative, K R ) from the Payra River, southern Bangladesh using many specimens of small to large sizes over a period of six months. 2. Materials and Methods 2.1. Study Area and Sampling: The present study was carried out in the Payra River (Fig. 1), a southern coastal river of Bangladesh situated in the Patuakhali district (straddling 22º 35´ N and 90º 26´ E). A total of 215 specimens of R. rasbora were collected occasionally from that region over the period from July to December-2019, using different types of fishing gears; gill net (mesh size: 1.5–2.5 cm), square lift net (mesh size ~1.0 cm) and cast net (mesh size: 1.0–2.0 cm). Fish samples were quickly chilled in ice on site and then preserved in 10% buffered formalin in laboratory until examination. For each specimen, lengths (total length, TL and standard length, SL) were measured by digital slide caliper (Mitutoyo, CD‐6"CSX), and the body weight (BW) was measured using an electronic balance (AND, FSH, Korea), to the nearest 0.01cm and 0.01 g precision, respectively. Figure 1. Map showing location of the study area for R. rasbora in the Payra River, southern Bangladesh. 2.2. Length Frequency Distribution (LFD): LFD for total population of R. rasbora was constructed using 1.0 cm intervals of TL. 2.3. Length-weight Relationships and Length-length Relationship (LWRs and LLR): The relationship between length and weight was calculated using expression: W= aLb (Le Cren, 1951) where the W is the whole body weight (g), L the total length (cm), a intercept of the regression and b is the regression coefficient (slope). The parameters a and b of the weight-length relationship will be estimated by linear regression analysis based on natural logarithms: ln (W) = ln (a) + b ln (L) (Frose, 2006; Hossain et al., 2016a). According to Froese (2006), all extreme outliers were excluded from the analyses. A t-test was applied to determine significant differences from the isometric value (b= 3.0 for length-weight relationship and b = 1.0 for length-length relationship) (Sokal and Rohlf, 1987). Deviation of the b value from the theoretical isometric value indicates either positive (b > isometric value) or negative (b < isometric value) allometric growth. Analysis of covariance (ANCOVA) (Zar, 1984) was used to test for significant differences in slopes and intercepts among the relationships. Additionally, the LLR for SL vs. TL was estimated by linear regression analysis (Hossain et al., 2006). © 2021 Jordan Journal of Biological Sciences. All rights reserved - Volume 14, Number 1 The form factor (a 3.0 ) of R. rasbora was estimated using the equation of Froese (2006) as: a 3.0 = 10 log a – s (b-3), where a and b are the regression parameters of LWR, and is the regression slope of ln a vs. b. The researchers used a mean slope S = -1.358 (Froese, 2006) for calculating the form factor because there was no available information on LWR for this species to estimate the regression (S) of ln a vs. b. 2.5. Size at First Sexual Maturity (L m ): The size at first sexual maturity (L m ) of R. rasbora was calculated using the equation proposed by Binohlan and Froese (2009) as: log (L m ) = ˗0.1189 + 0.9157×log (L max ); where, L m = size at first sexual maturity in TL, L max = maximum length (TL) of R. rasbora in the present study. Furthermore, the maximum length of R. rasbora was obtained from available literature in the FishBase used to estimate L m for water bodies throughout the world. 2.6. Condition Factor: The allometric condition factor (K A ) was calculated by the equation of Tesch (1971): W/Lb, where W is the body weight (g), L is the TL (cm), and b is the LWR parameter. Fultonʹs condition factor (K F ) was estimated using the equation of Fulton (1904): K F =100× (W/L3), where W is the body weight (g), and L is the TL in cm. The scaling factor of 100 was used to bring the K F close to unit (Froese, 2006). In addition, the relative condition factor (K R ) was analyzed following the equation of Cren (1951): K R = W/(a×Lb), where W is the body weight (g), L is the total length (cm), and a and b are LWR parameters. 2.7. Statistical Analysis: For statistical analysis, Microsoft® Excel-add-in DDXL and GraphPad Prism 8 software were used. The Spearman rank-correlation test was applied to analyze the relationship of condition factors with TL and BW. All statistical analyses were considered significant at 5% (p<0.05). 3. Results 3.1. Length Frequency Distribution (LFD) During the study period a total of 215 specimens of R. rasbora were collected from the Payra River, southern Bangladesh. The length frequency distribution of R. rasbora is shown in (Figure 2). Table 1 shows the descriptive statistics of maximum and minimum length and weight measurement of R. rasbora. LFD showed that the range of TLs was 2.6 to 12.5 cm (Fig. 2), and that body weight ranged from 0.22 to 10.65 g there. The 4.00 to 4.99 cm TL size group was numerically dominant and constituted 41.86% of the total population (Figure 2). 131 Table 1. Length (cm) and weight (g) measurements of combined sexes of Rasbora rasbora (Hamilton, 1822) from the Payra River, southern Bangladesh, July 2019 to December 2019. Measurement Total Total length (TL) Standard length (SL) 215 Body weight (BW) Min Max Mean±SD 2.6 12.5 5.58±2.34 2.4 10.5 4.40±1.99 0.22 10.65 2.30±3.12 n, sample size; Min, minimum; Max; maximum and SD, standard deviation 60 Frequency (%) 2.4. Form Factor (a 3.0 ): 40 20 0 1 2 3 4 5 6 7 8 9 10 11 12 13 Class interval Figure 2. Total length frequency distribution of R. rasbora in the Payra River, southern Bangladesh. 3.2. Length -Weight Relationships (LWRs) The sample size (n), regression parameter, 95% confidence interval of a and b, coefficient determination (r2), and growth type (GT), of R. rasbora are shown in Table 2. In the present study, the calculated allometric coefficient (b=2.79) and t-test value (t s =-7) of TL vs. BW indicates a negative allometric growth pattern (Figure 3), as did the SL-BW relationship (Table 2 and Figure 4) in the Payra River. The LWRs were highly significant (p<0.0001) with r2 values >0.963. Table 2. Descriptive statistics and estimated parameters of the length–weight and length-length relationships of R. rasbora (Hamilton, 1822) from the Payra River, southern Bangladesh. Species n Regression parameters 95% CI of a 95% CI r2 of b GT a b 0.0120 2.79 0.011 to 0.014 2.726 to 0.969 A2.862 BW = a*SLb 0.0290 2.66 0.026 to 0.032 2.604 to 0.963 A2.747 TL=a+b*SL 0.441 1.169 0.355 to 0.525 1.151 to 0.988 A+ 1.186 BW =a*TLb 215 n, sample size; TL, total length; SL, standard length; BW, body weight; a, intercept; b, slope; CI, confidence interval; r2, coefficient of determination; GT, growth type; A-, negative allometric; A+, positive allometric. © 2021 Jordan Journal of Biological Sciences. All rights reserved - Volume 14, Number 1 132 3.5. Size at First Sexual Maturity (L m ) 18 Body weight (g) 15 Size at first sexual maturity for combined sex of R. rasbora was estimated as 7.96 (~8.00) cm TL in the Payra River. BW= 0.0120 (TL)2.79 n=215, r² = 0.969 12 9 3.6. Condition Factors 3.6.1. Allometric Condition Factor (K A ) 6 3 0 0 2 4 6 8 Total length (cm) 10 12 14 Figure 3.Total length-body weight relationship of R. rasbora in the Payra River, southern Bangladesh. Table 3. Condition factors of R. rasbora (Hamilton, 1822) in the Payra River (southern Bangladesh). 18 Body weight (g) 15 BW = 0.0290 (SL)2.66 n=215, r² = 0.962 12 The estimated K A of R. rasbora ranged from 0.00630.0570 (Mean ±SD, 0.0128±0.0040) (Table 3). According to Spearman rank-correlation tests, there was a significant relationship between BW vs. K A (r s = 0.2219, p = 0.0011), but not between TL vs. K A (r s = 0.0532, p = 0.4375) (Table 4). 9 6 Condition factors Min Max Allometric condition factor (K A ) 0.0063 0.0570 0.0128±0.0040 Mean±SD Fulton’s condition factor (K F ) 0.3933 4.1844 0.9110±0.2968 Relative condition factor (K R ) 0.5223 4.7535 1.0638±0.3329 3 Min, minimum; Max, maximum; SD, standard deviation 0 0 2 4 6 8 Standard length (cm) 10 12 Figure 4. Standard length-body weight relationship of R. rasbora in the Payra River, southern Bangladesh. 3.3. Length-length Relationship (LLR) The length-length relationship between TL and SL of R. rasbora along with the estimated parameters of the LLR and the coefficient of determination (r2), are shown in Table 2 and Figure 5. During this study, the calculated allometric coefficent (b=1.16) and t-test value (t s =20) of the LLR indicates positive allometric growth pattern. The LLR was highly significant (p<0.0001) with a coefficient of determination values of 0.988. Table 4. Ralationships of condition factor with total length (TL) and body weight (BW) of R. rasbora (Hamilton, 1822) in the Payra River, southern Bangladesh. Relationship r s value 95% CL of r s p values Significance TL vs. K A 0.05322 -0.08511 to 0.1895 0.4375 ns TL vs. K F -0.2354 -0.3614 to -0.1009 0.0005 *** TL vs. K R 0.05312 -0.08522 to 0.1894 0.4384 ns BW vs. K A 0.2219 0.08682 to 0.3489 0.0011 ** BW vs. K F -0.0611 -0.1971 to 0.07726 0.3727 ns BW vs. K R 0.2218 0.08673 to 0.3488 0.0011 ** 14 TL= 1.169 (SL) + 0.441 n=215; r² = 0.988 12 Total length (cm) 10 4 TL, total length; BW, body weight; K A , allometric condition factor; K F ; Fulton′s condition factor; K R , relative condition factor; r S , Spearman rank-correlation values; CL, confidence limit; p, shows the level of significance; ns, not significant; * significant; ** highly significant; ***very highly significant. 2 3.6.2. Fulton’s Condition Factor (K F ) 8 6 0 0 2 4 6 8 10 12 Standard length (cm) Figure 5. Total length-standard length relationship of R. rasbora in the Payra River, southern Bangladesh. 3.4. Form Factor (a 3 . 0 ) The a 3.0 was calculated as 0.007 for combined sex of R. rasbora in the Payra River, southern Bangladesh, and this value indicates that this fish is elongated in shape. The calculated K F ranged from 0.3933-4.1844 (Mean ± SD, 0.9110±0.2968) (Table 3). According to Spearman rank-correlation tests, there was a significant relationship between TL vs. K F (r s = -0.2354, p = 0.4375), but not between BW vs. K F (r s = -0.0611, p = 0.3727) (Table 4). The lowest K F value was found in the size of 12 cm, whilst the highest in 2 cm for both sexes. Furthermore, the K F value started decreasing after 9.0 cm TL (Figure 6). © 2021 Jordan Journal of Biological Sciences. All rights reserved - Volume 14, Number 1 Fulton's Condition Factor (KF) 1.4 1.2 1 0.8 0.6 0.4 0.2 0 0 2 4 6 8 10 12 14 Total length (cm) Figure 6. Fulton’s condition factor (K F ) with regard to total length (cm) for R. rasbora in the Payra River, southern Bangladesh. 3.6.3. Relative Condition Factor (K R ) The K R of R. rasbora ranged from 0.5223-4.7535 (Mean ± SD, 1.0638±0.3329) during this study (Table 3). From Spearman rank-correlation tests, K R showed a significant relationship with BW (r s =0.2218, p =0.0011), but not with TL (r s = 0.0531, p =0.4384) (Table 4). 4. Discussion: According to the statement of the local fishers, this fish is mostly abundant during the summer (June-August) and autumn (September-October); other times they rarely found this species in the river which had made a great hindrance to collect fish sample from January to May. In our study, it was not possible to sample individuals of R. rasbora from January to May, for one or more of the following reasons: the biased selection of fishing gear or fishermen did not go where the fish were or possibly because of the fish’s absence on the fishing grounds, and/or because fishermen discarded smaller fish (Rahman et al., 2018) or the degradation of ecology of the Payra River, which signals the need for urgent measures to conduct extensive studies on these species to provide more information for their management and conservation. In present study, it was not possible to collect the R. rasbora smaller than 2.6 cm, which was attributed to either the absence of small sized fishes (<2.6 cm TL) in the populations or the fishermen did not go where the smaller size exist (Azad et al., 2018, Khatun et al., 2018) or selectivity of fishing gears (Hossain et al., 2012 a, b). Furthermore, the maximum length of R. rasbora within the Payra River was 12.5 cm TL which is slightly lower than the maximum recorded value of 13.0 cm TL (Froese and Pauly, 2019). Most likely, this growth differences can be attributed to differences in environmental factors, particularly water temperature and food availability (Ahamed and Othomi; 2012). Generally, maximum length is considered as a functional tool for fisheries resource planning and management, and is utmost for the determination of asymptotic length and growth coefficient of fishes (Hossain et al., 2019; Khatun et al.,2019; Ahmed et al., 2012; Hossain et al., 2016b, 2017; Nawer et al., 2017; Hossen et al., 2016, 2018). In the current study of R. rasbora, the estimated b values ranged from 2.67 to 2.79 for LWRs from the Payra River which were within the usual range (2.50 to 3.50) of b values for fishes (Carlander, 1969; Froese, 2006). To the 133 best of our knowledge, no references dealing with LWRs for the studied species are available; thus it was not possible to compare the present results with previous references. Hence, the present study was compared with results from studies dealing with other species of the Cyprinid family. In this study, estimated b values of the LWRs (TL vs. BW; SL vs. BW) were <3 suggesting fish becomes more slender as the length increase for R. rasbora in the Payra River which was generally in agreement with results for fishes of same family and same genus (R. daniconius) obtained from the Sharavathi Reservoir, Karnataka (Kumar et al., 2005). The length-weight relationship parameters (a and b) are influenced by a series of factors including season, habitat, gonad maturity, sex, diet, stomach fullness, health of the individuals in their natural habitats as well as the treatment of specimens and preservation techniques after sampling (Bagenal and Tesch, 1978; Tesch, 1971). However, LLR for the R. rasbora was highly correlated (r2=0.988; p<0.0001). Since the current study is also the first assessment on LLR of R. rasbora, so lack of references dealing with LLR constrains the comparison of the present results with previous literature on the same population/ species. Form factor (a 3.0 ) can help to determine whether the body profile of individuals in a particular population or species differs from others (Froese, 2006). The estimated a 3.0 for R. rasbora was within the limits 0.00775–0.00906 reported by Frose (2006); suggesting that this fish is elongated in shape in the Payra River. No references dealing with a 3.0 for this species are in the literature to make comparison across the water bodies. Though most of the studies deal with single condition factor, we have, however, worked on three condition factors (K A ; K F and K R ) to evaluate the physical and habitat status of R. rasbora. Furthermore, study on relative condition factor (K R ) in preference to the ponderal index (K) is recommended as the latter is generally influenced by many environmental and biological factors (Le Cren, 1951). The studied fish species has K R >1, which indicates good general conditions of the fish (Le Cren, 1951). Generally, condition factor is influenced by many factors like sex, season, environmental factors, stress, gonadal development and availability of forage items (Lambert and Dutil, 1997; Zargar et al., 2012; Ali et al., 2014). Furthermore, the lowest K F value was found in the size of 12 cm, whilst the highest in 2 cm for both sexes. The K F with regard to length class showed a noticeable decrease after 9.0 cm for combined sexes, which might be attributed to the start of sexual maturation, as indicated in the present study, which recorded the size at first sexual maturity of R. rasbora as ~8.00 cm. Therefore, the size at first sexual maturity of R. rasbora could be around 8.0 cm TL in the Payra River, southern Bangladesh. Studies on L m are very atypical (except Hossain et al., 2019, 2010, 2016a, 2017). This is the first study on size at first sexual maturity (L m ) for R. rasbora worldwide. Thus, our study will be the base for more thorough studies. 5. Conclusion: The 4.00 to 4.99 cm TL size group (41.86%) was numerically dominant and fish becomes more slender as the length increases in the Payra River. The fish is elongated in body shape and ensures good general 134 © 2021 Jordan Journal of Biological Sciences. All rights reserved - Volume 14, Number 1 conditions of the fish in the Payra River. The size at first sexual maturity of R. rasbora could be around 8.0 cm TL in the Payra River, southern Bangladesh. This study provides valuable information for the online Fish Base database, as well as providing an important baseline for future studies within the Payra River and surrounding ecosystems, as no information on the biological aspects of this species are currently available in the literature. Moreover, further detailed studies (with considering sampling period throughout the year) on spawning frequency and some other biological aspects, i.e. growth and abundance, are still necessary for the future management of this species. Acknowledgements We express our gratitude to (i) the local fishers of Payra (Patuakhali, southern Bangladesh) for collecting samples, and (ii) the Chairman (Department of Fisheries Management, Patuakhali Science and Technology University, Bangladesh) for use of the laboratory facilities. Conflicts of Interest The authors declare that there is no conflict of interest regarding the publication of this paper. References Ahamed F and Ohtomi J. 2012. 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