Abstract
Morphometric characteristics, length-weight relationships (LWRs), and condition factors (K) were studied for five indigenous fish species belonging to five different families (Barilius barila Hamilton, Cirrhinus reba Hamilton, Chanda nama Hamilton, Mystus bleekeri Day, and Clupisoma garua Hamilton), from the River Ganga in Bihar, India. A total of 557 fish individuals were collected seasonally from September 2021 to August 2022 using a monofilament drift gill net and a conical trap net Khairel jal. In morphometric analysis, the highest degree of correlation was observed between the total length and the standard length for all species (except C. garua). The estimated exponent value b varies from 2.920 to 3.214, where the slopes of regression lines among the species have significant differences (). The b value indicated that three species (B. barila, C. nama, and C. garua) follow positive allometric growth, whereas M. bleekeri shows isometric growth and C. reba exhibits negative allometric growth. The condition factor value for these fishes ranged from 0.67 to 0.98, which indicated that the population of C. reba was robust compared to all other species (). A new maximum length (146.8 mm) was obtained for B. barila from India. The present study gives baseline biological information on five commercially important indigenous fish species found in the River Ganga, Bihar. As the population of these species has been dwindling in recent times, these data will be important for the conservation and sustainable utilization of these important species in the long run.
1. Introduction
Ganga is the largest river system in India and is home to around 300 freshwater fish species that support 10–13 million riverine fishers’ livelihoods and nutritional security [1]. Many freshwater fish species have become critically endangered as a result of human interventions, including the building of multipurpose dams and barrages, overfishing, pollution, invasions of exotic species, climatic changes, and soil erosion [2–4]. Approximately 480 kilometers of the River Ganga flow through Bihar, and fish were caught using traditional fishing gear (monofilament drift gill nets and Khairel jal). Annual fish landings from the Patna stretch of this river were 7.4 tons [5], while Bihar’s total fish production was 0.64 metric tons with an annual per capita fish consumptions rate of 8.82 kg [6]. In local fish markets, catfish sell for 300–400 rupees per kilogram (US$ 3.67–4.89), while minor carps sell for 100–150 rupees per kilogram (US$ 1.22–1.83), but this depends on availability and season. The study of the biological parameters of fish species provides valuable information for management and sustainable use. Morphometric characters are frequently used to identify fish species [7] and determine whether a stock is heterogeneous or homogeneous [8]. The length-weight relationship of fish is a useful index for evaluating growth, survival, maturity, reproduction, and general well-being [9]. It explains the change in weight of fish with respect to length and vice versa [10]. It is often used to estimate fish biomass when the length-frequency distribution is known [11], to determine possible differences between separate unit stocks of the same species [12] and to estimate the mean weight of fish based on known length [13]. It also serves as a tool to assess the life history characteristics of fish populations, such as stock composition, age at sexual maturity, and lifespan and provides important insights into resource conservation [14, 15]. Similarly, the condition factor provides information on the health status of species and the community as a whole [16] and can be used to compare the physiological robustness of fish on a numerical basis [17]. In recent times, increased pollution, reduced water flow, and the use of nonscientific fishing methods have had an impact on the morphological and physiological statuses of fish species. In spite of their commercial and ecological importance, there is still a scarcity of information on morphometric characteristics, length-weight relationship, and condition factors, for numerous fish species from the River Ganga. Therefore, the present study aimed to generate baseline data on these parameters of five indigenous fish species, the Barilius barila Hamilton, Cirrhinus reba Hamilton, Chanda nama Hamilton, Mystus bleekeri Day, and Clupisoma garua Hamilton, belonging to the families, Danionidae, Cyprinidae, Ambassidae, Bagridae, and Schilbeidae, respectively.
2. Materials and Methods
2.1. Study Area
Fish were collected at seasonal intervals from Digha Ghat Patipul (25°40′8.4″N; 85°0′18″E), a fish landing site of the River Ganga in Bihar, India (Figure 1). A total of 557 specimens of five indigenous fish species were collected from September 2021 to August 2022. These four-season samples were pooled for statistical analysis. Fish specimens were caught using a monofilament drift gill net (100–200 m length, 1.5-2 m width, 10–30 mm mesh size, and 4–6 hours” of operational time) and a conical trap net/Khairel jal (7-8 m length, 10 m mouth width, 1 m cod end width, and cod end mesh size 5–10 mm). Freshly caught fish specimens were kept in an ice box and brought to the laboratory. Fish specimens were identified to the species level using the standard manuals/taxonomic literature [18, 19]. The total length of specimens was measured from the tip of the snout to the tip of the caudal fin to the nearest 1 mm using a digital Vernier caliper (Insize - 0/150 mm), and wet weight was recorded to the nearest 1 g using a digital balance (WENSAR TM-MAB 220).
2.2. Morphometric Characters
The morphometric characters were recorded in the laboratory in a fresh condition using standard methods [20, 21]. The morphometric traits measured were total length (TL), standard length (SL), predorsal length (PDL), prepectoral length (PPL), prepelvic length (PVL), preanal length (PAL), caudal peduncle depth (CPD), head length (HL), snout length (SNL), eye diameter (ED), postorbital length (POL), interorbital length (IOL), caudal fin length (CFL), and body depth (BD). Linear regressions were performed for the compared traits using the least squares method [22]. For meristic traits, the number of rays in the dorsal (DFR), pectoral (PFR), ventral (PVR), anal (AFR), and caudal fin (CFR) was counted. In addition, the number of gill rakers on the first-gill arch (GR) was analyzed. Descriptive statistics were performed for the meristic counts.
2.3. Length-Weight Relationships (LWRs)
The length-weight relationships were established separately for each species using the equation [9], where W = body weight (g) of the fish specimens, L = total length (mm), a = intercept, and b = slope of the regression line. Furthermore, the relationship was expressed in the logarithmic form . A T-test was applied to determine whether the regression coefficients differ significantly from the isometric value of 3 (). The isometric growth is considered for a fish species when the estimated regression coefficient value is close to 3. In contrast, if it deviates from 3, fish growth becomes either negative allometric (b < 3) or positive isometric (b > 3).
2.4. Condition Factor
Condition factor (K) of the studied fish species was determined as per Fulton’s index K = [23]. Here, “K” is the condition factor, “W” is the total body weight (g) of fish specimens, and “L” is the total length of specimens (mm).
2.5. Data Analysis
A statistical analysis of all the data was performed using Graph Pad Prism software. These fish’s length and weight parameters are recorded in millimeters (mm) and grams (g). The data were presented as mean ± SD.
3. Results
3.1. Morphometric Characters
Table 1 shows the regression of total length (TL) on standard length (SL), predorsal length (PDL), prepectoral length (PPL), preventral length (PVL), preanal length (PAL), caudal peduncle depth (CPD), head length (HL), snout length (SNL), eye diameter (ED), postorbital length (POL), interorbital length (IOL), caudal fin length (CFL), and body depth (BD). For B. barila, C. reba, C. nama, and M. bleekeri, the correlation coefficient shows the highest degree of correlation between the total length and standard length, while for C. garua, it shows the highest correlation between the total length and head length. The correlation coefficient reveals the lowest degree of correlation between the total length and caudal fin length, snout length, and postorbital length for B. barila, C. nama, and C. garua. Descriptive statistics for meristic counts are shown in Table 2. For each species, the gill rakers had the highest coefficient of variation, while the caudal fin ray, ventral fin ray, and pectoral fin rays of B. barila, C. reba, and C. nama had the lowest coefficient of variation. Based on the Kruskal–Wallis multiple comparison tests, the mean values of the gill rakers of B. barila were statistically different from those of C. garua (). The mean of C. reba is significantly different from C. nama () and C. garua (), while M. bleekeri is also significantly different from C. nama () and C. garua (). The mean value of gill rakers in C. reba and M. bleekeri is not statistically significant (). The results indicate that there are no significant differences in morphological characters and meristic counts of these species within their populations, indicating that the stocks of these fish that occur along the Ganga River are homogeneous. Therefore, the fin formula based on meristic counts can be written as follows: D08–10 P11–15 V08–10 A10–13 C18–24 GR19–26 for B. barila; D09–11 P13–16 V09-10 A07–09 C21–24 GR24–39 for C. reba; DVII, 15–17 P11-12 VI, 05-06 AIII, 14–16 C22–24 GR16–20 for C. nama; DI, 6–8 PI, 6–8 V06-07 A07–11 C18–22 GR20–38 for M. bleekeri; and DI, 6–8 PI, 10–12 V06-07 A29–36 C19–24 GR13–20, for C. garua.
3.2. Length-Weight Relationships (LWRs)
Table 3 shows the descriptive statistics about the length-weight relationship for five indigenous fish species. The LWRs were determined to be W = 0.00000279 L3.241 for B. barila, W = 0.0000129 L2.920 for C. reba, W = 0.00000148 L3.192 for C. nama, W = 0.006 L3.013 for M. bleekeri, and W = 0.004 L3.145 for C. garua. Furthermore, the corresponding logarithmic form was noted as follows: log W = −12.79 + 3.241 log L for B. barila; log W = −11.26 + 2.920 log L for C. reba; log W = −12.39 + 3.192 log L for C. nama; log W = −5.11 + 3.013 log L for M. bleekeri; and log W = −5.51 + 3.145 log L for C. garua. The exponent b value ranged from 2.920 to 3.214, and the slopes of the regression lines among the species differed significantly (). An exponent b value reveals that the three species (B. barila, C. nama, and C. garua) show positive allometric growth (b > 3), whereas M. bleekeri shows isometric growth (b = 3.013) and C. reba exhibits negative allometric growth. The observation confirms that the exponent value b is species-specific, and each fish species has a specific growth rate.
3.3. Condition Factor
In all specimens of B. barila, C. reba, C. nama, M. bleekeri, and C. garua, condition factor values ranged from 0.69 to 0.93, 0.81 to 1.46, 0.88 to 1.03, 0.81 to 1.02, and 0.57 to 0.82, with a mean (mean ± SD) of 0.81 ± 0.07, 0.98 ± 0.18, 0.94 ± 0.06, 0.91 ± 0.03, and 0.67 ± 0.05, respectively (Figure 2). Based on the Kruskal–Wallis multiple comparison tests, the mean values of C. garua were significantly different from the mean values of M. bleekeri (), C. nama (), and C. reba (), respectively.
4. Discussion
The morphometric data revealed that the regression coefficient has a varying strength relationship between the total length and other characters for each species. These variations are species-specific and depend on the ontogenetic development of the species. In meristic counts, the number of rays in the dorsal, pectoral, ventral, caudal, and anal fins varies within the size range of B. barila (97–123), C. reba (102–152), C. nama (74–83), M. bleekeri (77–119), and C. garua (138–216), confirming that meristic counts depend on body size and vary with fish growth. Gill rakers are significantly more numerous in planktivorous fish (C. reba) compared to carnivorous fish (C. garua and C. nama), confirming that gill rakers depend on the feeding habits and food preferences of the species. Morphometric plasticity tends to respond to local environmental vitiations related to niche patterns of resource use [24] and physical characteristics of habitats that determine biological, evolutionary, and ecological changes in morphological traits of fish populations [25].
The length-weight relationship is important for understanding fish’s growth rate and the pattern. The estimated b values for these indigenous fishes (2.92–3.24) were consistent with the expected range of 2.5–3.5 [10]. C. reba has a relatively slow growth rate and tends to be thinner (almost all specimens are in the juvenile stage), whereas estimates for B. barila are significantly better. 24.53% of individuals in the entire population of B. barila are sexually mature, and these mature specimens range in length from 73 to 123 with a mean length of 108.35 ± 10.55 mm (mean ± SD). In mature specimens, two-thirds of the entire body cavity are occupied by mature ovaries. Furthermore, recorded mean values for the length and weight of these ovaries are 45.90 ± 3.64 and 1.74 ± 0.69, respectively (mean ± SD). Fish fecundity and egg diameter (mm) were calculated to be 3150 ± 1452.62 and 0.77 ± 0.05, respectively. The maximum length observed for B. barila (146.8 mm) was higher than previously recorded for this fish (139.5 mm) from the Manas River in Assam, India [26]. The condition factor K is an important factor to explain the relative robustness of fish. The largest variation in K was found in C. reba, whereas the least variation was found in C. garua. Despite their dissimilar food preferences and different physical forms in the juvenile and adult life stages, the species showed variation in K. In addition, size composition, seasonal sampling, and a limited number of specimens affect the K value of fish. Furthermore, it is also influenced by reproductive status, seasonality of natural diet, and age of fish [10, 27]. In conclusion, the present study on these parameters is perhaps the first detailed report on these five indigenous fish species from River Ganga, Bihar, India. These findings will provide valuable information to the fisheries biologists of the region to study their population parameters and formulate appropriate management measures for the sustainable exploitation of these resources.
Data Availability
The data used to support the findings of this study are available from the corresponding author upon reasonable request.
Conflicts of Interest
The authors declare that they have no conflicts of interest.
Acknowledgments
This research work has been made possible by the funding support from the Indian Council of Agricultural Research, New Delhi.