Abstract

The length–weight relationship (LWR) and condition factor (CF) are widely used tools in fisheries biology to assess growth patterns, well-being and population status of fish. However, baseline datasets from earlier decades remain scarce for many Indian freshwater fishes, including the commercially important Mastacembelus armatus and Macrognathus aculeatus. In the present study, LWR and CF were estimated from 494 M. armatus (Total length- 18.7 cm to 53.7 cm and total weight- 40 g to 350 g) and 561 M. aculeatus (Total length- 9.2 cm to 30.3 cm and total weight- 10 g to 100 g) collected from the Godavari River between 2005 and 2007. The regression equation obtained was W = aLᵇ, with a value of a = -0.285 and b = 1.5106. for M. armatus and with a value of a = -0.98 and b = 1.94 for M. aculeatus. The growth exponent b approximated is lesser than 3 for both the fishes, indicating negative allometric growth. The relative condition factor (K) was 1.01 ± 0.15 for M. armatus and 1.04 ± 0.315 for M. aculeatus, reflecting the overall well-being of the species during the study period. LWR was significant at P < 0.01 for both mastacembelid fish species, with the coefficient of determination (R2) for M. armatus (R2= 0.802) and M. aculeatus (R2= 0.584) respectively. This dataset provides a historical baseline for two mastacembelid fish in the Godavari River, against which contemporary populations can be compared in light of anthropogenic pressures, habitat modifications, and climate change. Such long-term biological records are valuable for fisheries management, ecological monitoring, and conservation planning in Indian River systems.

Keywords:Length- weight relationship, Condition factor, Mastacembelus armatus, Macrognathus aculeatus, Godavari River, Historical dataset, Baseline fisheries biology.

Introduction

Fish are an integral part of the ecosystems as they support food webs, maintain ecosystem resilience and are good source of food to humans [1,2]. Fish is an importance source of high-quality protein, omega 3-fatty acids, nutrients and mineral [3]. Rivers are vital ecosystems providing food to millions of people all over the world, support biodiversity and serve as key indicator of river ecosystem health. River Godavari is the second longest river in India originating from Maharashtra, traversing through Telangana, Andhra Pradesh, Chhattisgarh and Orissa and is a home to a wide variety of freshwater fish [4-9]. Biometric studies in fisheries management is one of the leading factors used to assess the biomass and stock condition of fish species [10-15]. A significant aspect of morphometric investigations is evaluating the species growth characteristics based on the length-weight relationship, as well as the health of fish species influenced by various bio-ecological factors [16-18]. Fish species are considered to be apposite for biological assessment due to their easy identification, taxonomic importance, broad tolerance, sensitivity to environmental change and integration of stressors [13, 19]. Several studies illustrate that calculating the correlation between length and weight (LWR) can be imperative in classifying fish species [20-24]. This type of studies will provide the information about the biography of fish, health condition and other biometric characters along with growth pattern, well-being and ecological condition of an aquatic environment [20,25,26]. The length-weight relationship acts as an imperative tool in fish population estimation models studies, aquatic biome modeling, gonad development, and maturity status to estimate weight-at-age [27,28]. The condition factor is also considered as an essential characteristic by fisheries scientists that enable to understand the physiological state of the fish and how it impacts its welfare [29,30]. LWRs allow conversion between length and weight, enabling biomass estimation from length-frequency dataimportant where weighing every specimen is impractical [22,31]. Condition indices (e.g., Fulton’s K, relative condition Kn) derived from LWRs are sensitive to food availability, reproductive status, parasitism and environmental stress, making them practical indicators of habitat quality [32,33]. Differences in b among life stages (e.g., juveniles vs adults) or sexes can reveal ontogenetic shifts in energy allocation (growth vs reproduction), informing management of spawning seasons, recruitment, and habitat protection. Repeated LWR patterns across populations can reflect inherent morphological constraints and adaptive responses to benthic/ nocturnal feeding strategies [27]. Regional comparisons (between river basins, seasons, or anthropogenic gradients) provide context for assessing resilience and vulnerability [18, 20, 30]. By comparing two fish populations that live in various ecological situations and evaluating the gonad development and feeding activity of these species, the condition factor (K) also offers information about their well-being [34-36]. Although numerous biometric studies were conducted on different water bodies in Andhra Pradesh, very few of these studies are from river Godavari during 2005 and 2007. Over the period, anthropogenic pressures from dams, sand mining, industrial pollution and climate change have brutally degraded the Godavari River’s fisheries [4, 37]. These pressures have caused a decline in native fish populations, changed habitats and threatened the livelihoods of local fishing communities. Though, the river has been noted for having good environmental conditions in some stretches, the overall effect has been a crisis for riverine biodiversity [9, 38-41]. Mastacembelid fishes (Family: Mastacembelidae) commonly known as spiny eels are a group of elongated, eel-like freshwater fishes characterized by an extended, tapering body, reduced or small scales, a long dorsal fin preceded by a series of isolated spines, and a pointed rostral region [42-45]. They restrict their habitat to South-East Asia and occupy a variety of lotic and lentic habitats such as rivers, streams, floodplain wetlands and vegetated margins [46-48]. They are often benthic, enigmatic and nocturnally active, adapted for burrowing or hiding in substrate and vegetation and thus, form a firm basis of several economically important fisheries in Southern India [49- 52]. The spiny eels, Macrognathus aculeatus Bloch (lesser spiny eel) and Mastacembelus armatus Lacepede (giant spiny eel) are often noted as an important food and aquarium species in parts of southern and eastern India and highly relished as ‘Bommidai’ due to their rich source of proteins, vitamins and medicinal value [53-57]. They have great palatability and high consumer appeal in India and neighboring countries as they play an important role to meet the nutritional requirements of common people [58]. There are reports on parasites of mastacembelid fishes during the study period, but the LWR studies are scarce [59-63]. For mastacembelid fishes, published LWR studies have reported a range of b values (often below 3) reflecting their elongated body form and ecological habits; several regional studies on Mastacembelus and Macrognathus species provide LWR parameters, condition factor analyses, and seasonal/size-class comparisons [64-66]. These studies are essential for understanding species-specific growth patterns, condition and health, population dynamics, stock assessment, and for guiding conservation or exploitation measures [67-70]. There were no comparative account studies on LWR dataset of mastacembelid fishes of River Godavari during the study period, however, LWR studies on mastacemblids from different river basins was performed [71-73]. Hence, this study quantifies LWRs of two species of mastacembelid fishes and calculates K to determine the environmental condition of River Godavari during 2005-2007 which can provide a comparative baseline to the scientists working on LWRs and condition factor of fishes of River Godavari. Historical baseline studies of this kind are of paramount importance as they can help in emphasizing the ecological conditions of river Godavari and its biodiversity during the years 2005–2007 i.e., before major industrial expansions and river alterations in the Godavari.

Material and Methods

A total of 1055 specimens (494- M. armatus and 561- M. aculeatus) were collected monthly from 2005 to 2007 from local fishermen and nearby fish markets of River Godavari (Figure 1). The specimens were brought to the laboratory to conduct the biometric analysis. The total length was measured from the tip of the snout to the end of the caudal fin ray to the nearest cm using a measuring scale, and the weight of the fish was estimated to the nearest gram by using a weighing balance. The data were grouped into four sets of samples i.e., total, male, female and juveniles.

The length weight relationship (LWR) was calculated by using Le Cren’s (1951) formula [74].
W= aL^b
Where ‘W’ is the weight of the fish in grams (g), L is the total length of the fish in centimetres (cm), ‘a’ is a constant and ‘b’ is the exponent of growth. A linear relationship formula can be attained by expressing a logarithmic function

Log W= Log a + b Log L
Where ‘W’ is weight of the fish in grams (g), ‘L’ is the length in cm. ‘Log a’ is the intercept of the regression line and ‘b’ is the slope of the regression line. The relative condition factor Kn, is a measure of the well-being or stoutness of a fish was determined using length weight data of fish samples and is designed by Le Cren (1951) formula:
Kn = W / aL^b
Where ‘W’ is the observed weight and ‘aLb’ is the calculated weight.

Results and Discussion

A total of 494- M. armatus (TL- 36.54±6.68 cm, Range- 18.7- 53.7 cm; TW- 121.83±39.22 g, Range- 40-350 g) and 561- M. aculeatus (TL- 19.7±3.71 cm, Range- 9.2-30.3 cm; TW- 36.32±16.1 g, Range- 10-100 g) specimens were analyzed for length-weight relationship (Figure2). Of the 494 M. armatus, 273 were females (TL- 37.4±6.59 cm, Range- 20.9-53.7 cm; TW- 125.6±41.77 g, Range- 40-350 g) and 221 males (TL- 35.43±6.64 cm, Range- 18.7-52.3 cm; TW- 116.27±36.73 g, Range- 40-270 g). Of the 561 M. aculeatus, 281 were females (TL- 20.66±3.63 cm, Range- 12.9- 30.3 cm; TW- 40.25±16.83 g, Range- 10-100 g), 236 males (TL- 19.63±3.11 cm, Range- 9.2-27.2 cm; TW- 35.34±13.44 g, Range- 10- 75 g) and 44 were juveniles (TL- 14.07±1.46 cm, Range- 10.8-16.7 cm; TW- 16.54±6.50 g, Range- 10-30 g). Linear length regression equation between total length and weight of pooled, male, female and juvenile of the two species of fish were plotted.
M. armatus:
Pooled: Log W= -0.285+1.5016 Log L (R2= 0.8025)
Female: Log W= -0.28+1.503 Log L (R2= 0.541)
Male: Log W= -0.291+1.514 Log L (R2= 0.842)
M. aculeatus:
Pooled: Log W= -0.98+1.941 Log L (R2= 0.5837)
Juvenile: Log W= -1.243+2.120 Log L (R2= 0.347)
Female: Log W= -0.886+1.872 Log L (R2= 0.527)
Male: Log W= -0.667+1.694 Log L (R2= 0.438)

The b value of length-weight relationship of the two species ranged between 1.501 to 2.120. It was found that b value of juveniles was higher. The correlation coefficient obtained for M. armatus are total population (r=0.855), male (r=0.906) and female (r=0.819). The correlation coefficient obtained for M. aculeatus are total population (r=0.742), juvenile (r= 0.557), male (r=0.637) and female (r=0.725) (Table-1, Figure 3 & 4). A strong positive correlation exists between the variable’s length and weight; weight increases according to the increase in the length. The growth is considered as isometric when b=3; this is always the case in an ideal fish that retains its shape without any change [14, 75-77]. When a species exhibits isometric growth, b value will be close to 3. The weight of the fish will increase eight times when there is a double increase in the length of the fish i.e., length and weight follow cubic relationship. A difference in b value 3 signifies the direction and the rate of change of condition or form; if b<3 indicates reduction in condition of fish with an increase in length, i.e., negative allometry. Similarly, b>3 indicates an increase in length or condition i.e., positive allometry. The values of b usually tend to vary between 2.5 and 3.5 [78]. In the present study, the estimated b values of M. armatus were 1.510 (pooled), 1.503 (females) and 1.514 (males), indicating negative allometric growth in which fish body weight does not grow faster in relation to their length. Similarly, the b values of M. aculeatus were 1.941 (pooled), 2.120 (juveniles), 1.872 (females) and males (1.694). The lower b values of M.armatus and M. aculeatus is indicative of negative allometric growth where the increase in body weight is not proportional to the increase in length. Such a trend is characteristic of elongated, laterally compressed species belonging to the family Mastacembelidae. The comparatively low b value can be accredited to their slender body form, benthic and nocturnal feeding behavior, and low energy conversion efficiency, resulting in reduced body mass relative to length. Environmental and seasonal factors, such as fluctuations in food availability and spawning stress, may also influence the weightlength relationship. Similar observations have been reported in other studies on mastacembelid fishes, suggesting that negative allometric growth is typical for this group, reflecting their morphological adaptations and ecological niche [45, 47, 66, 72, 73, 79]. From the present study, the b value of juveniles of M. aculeatus is higher than the b values of mature fish. The rapid growth rate of juvenile fish compared to mature fish may be attributed to quick fish growth in terms of length before attaining maturity and extensive utilization of energy to growth of gonadal tissues instead of somatic tissues. Relative condition factor (Kn) proposed by Le Cren (1951), measures the individual deviation of the fish from the average weight for the length and signifies the health of a fish during a particular period of time [74, 78]. The relative condition factor (Kn) of Mastacembelus armatus and Macrognathus aculeatus exhibited values close to or slightly above unity, indicating that both species were generally in good physiological condition. In M. armatus, the Kn values recorded were 1.016 ± 0.16 (pooled), 1.005 ± 0.18 (female), and 1.008 ± 0.129 (male). These values suggest that the individuals were healthy and well-nourished, with minimal variation between sexes, implying similar feeding efficiency and environmental influence on growth. The Kn values near unity also indicate that the habitat provided adequate food resources and favorable ecological conditions for the species. Similarly, in M. aculeatus, the relative condition factor ranged from 0.93 ± 0.303 in juveniles to 1.067 ± 0.313 in females, with a pooled mean of 1.04 ± 0.315. The relatively low value in juveniles may be attributed to high metabolic demands during growth, while higher Kn in adult females reflects better energy reserves and possible gonadal development during the pre-spawning phase. Males also showed slightly elevated values (1.048 ± 0.311), indicating healthy condition and comparable feeding status. The increasing trend of Kn from juveniles to adults in M. aculeatus suggests a positive correlation between maturity and condition, emphasizing improved feeding and nutrient assimilation with age. Overall, the relative condition factors for both M. armatus and M. aculeatus during the study period indicate that the sampled populations were in stable health under favorable environmental and trophic conditions. The slight interspecific variation, with M. aculeatus exhibiting marginally higher Kn values, may reflect better adaptability or resource utilization efficiency of this species within the studied ecosystem. Since this dataset represents 2005– 2007 conditions, it provides a baseline for future comparisons, especially under current scenarios of anthropogenic pressure, pollution, and habitat alteration in the Godavari basin.

Conclusion

The current investigation on the length-weight relationship and relative condition factor of Mastacembelus armatus and Macrognathus aculeatus revealed a strong positive correlation between length and weight, signifying that weight increases proportionally with length in both species. The estimated b values, ranging from 1.501 to 2.120, demonstrated negative allometric growth, suggesting that body weight increases at a slower rate than length. This growth pattern is characteristic of elongated, laterally compressed mastacembelid fishes and may be influenced by morphological adaptations, benthic feeding habits and ecological factors such as food availability and spawning stress. The relative condition factor (Kn) values close to unity in both species signify that the studied populations were in good physiological condition and that the habitat presented favorable ecological and trophic conditions. The slightly higher Kn values observed in M. aculeatus, particularly in females, may reflect enhanced adaptability, feeding competence and gonadal development compared to M. armatus. The higher b value in juveniles of M. aculeatus implies rapid somatic growth prior to sexual maturity. Overall, the results emphasize that both M. armatus and M. aculeatus populations in the study area display stable health and growth patterns consistent with their ecological adaptations. The results can contribute to long-term monitoring of fish biology and can serve as reference points for population assessment, conservation management and future ecological monitoring of mastacembelid fishes in the River Godavari system.

Acknowledgement

The author is grateful to CSIR for providing financial assistance as JRF and SRF (CSIR Award No.CSIR 9/2(467)/2004/EMR.dt.07- 11-2004).

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