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Study on Certain Aspects of Biology, Length-weight Relationship and Condition Factor of Native Fish Species from Upper Brahmaputra River Basin, India

M
Moirangthem Kameshwor Singh1,*
S
Simi Gogoi1
C
Chandopal Saikia1,2
S
Susmita Sonowal1,3
N
Netranjally Saikia1
E
Emon Thakuria1
S
Sanabam Sujen Singh4
1Department of Life Sciences, Dibrugarh University, Dibrugarh- 786 004, Assam, India.
2Department of Zoology, Tingkhong College, Dibrugarh-786 612, Assam, India.
3Department of Zoology, Barnagar College, Sorbhog-781 317, Assam, India.
4North Eastern Council, Government of India, Shillong- 793 003, Meghalaya, India.

ABSTRACT

Background: The present study deals with the morphometric characters, feeding behavior (RLG and Ga.SI), length-weight relationship (LWR), condition factor (K) and reproductive parameters of four native fish species viz. Channa punctata, Channa gachua, Mystus cavasius and Mystus vittatus collected from upper Brahmaputra river basin, Assam. The Brahmaputra river system in northeast India is a global hotspot for aquatic fauna that shelters a rich and diverse gene pool, especially fish.

Methods: The detailed morphometric characters and meristic counts of the selected fish species (Total=200, n=50 for each species) were measured carefully. Twenty-six morphometric and seven meristic parameters were studied for each fish specimen. The study also examined feeding biology (relative gut length and gastro-somatic index) as well as key reproductive characters viz. gonadosomatic index, absolute and relative fecundity and ova diameter. Regression analysis between total body length and weight, ovary length and weight of the selected specimens have also been performed during the study.

Result: Present study recorded highest total length in M. cavasius (9.00-15.00 cm) and lowest in M. vittatus (5.60-8.10 cm). The RLG was observed highest in M. cavasius (0.631) and lowest in both C. gachua and M. vittatus (0.45). The regression coefficient (b) indicates negative allometric growth in C. punctata (b= 2.453) and M. vittatus (b= 2.849), while isometric growth was observed in C. gachua (b=3.064) and positive allometric growth in M. cavasius (b= 3.563). Moreover, the r-values for LWRs for all investigated fishes were found ≥ 0.88. The mean condition factor ranged from 0.76-1.35 in all the studied fish species reveals the good health status of the fishes. Absolute fecundity was recorded highest in M. vittatus (3234) and lowest in C. gachua (282). Similarly, relative fecundity was found highest in M. vittatus (840) and lowest in C. gachua (22). Mean GSI was recorded in the ranged of 3.25-63.09. Ova diameter was varied from 0.4-1.2 (cm). Regression analysis between total body length-weight and ovary length-weight of the selected species were also performed and observed strong and positive correlation (r value ranged from 0.797-0.891).

INTRODUCTION

The North-eastern Himalayan region is identified as one of the mega aquatic biodiversity hotspots of India. The Brahmaputra riverine system is enriched with diversified freshwater fish species and serves as lifeline of natural fisheries. These fishes have great significance in the life of mankind, being an important natural source of protein and providing certain other useful products as well as economic sustenance to many nations. It is a well-known fact that the knowledge on fish biology particularly on morphometry-meristic, length-weight relationship, condition factor, food and feeding habit, reproduction, etc. is of utmost importance not only to fill up the lacuna of our present-day academic knowledge but also in the utility of the knowledge in increasing the technological efficiencies of the fishery entrepreneurs for evolving judicious pisciculture management. Fish identification depends mostly on two main features: morphometric and meristic characters. Morphometric parameters of a fish species have a major role to ensure whether there is any disparity between the same species of different geographic regions (Naeem et al., 2012; Gogoi et al., 2025). Moreover, some variations may occur in the meristic counts (the number of spines and rays) or in the biometric indices i.e. in different body proportions in various length groups. Length-weight relationship, as a tool for fish conservation, is also crucial to the fish biologist. Estimation of length-weight relationship (LWR) is also considered to be a regular research work of fisheries scientists and has a wide range of application in the field of fish population dynamics (Froese, 2006). It helps to describe some of the basic biological characteristics and provide information on growth status of fishes (Tesch, 1968). Condition factor (K) is an important biological parameter, which indicates the suitability of a specific water body for growth of fish and an index of species average size (Alam et al., 2014, Nayak et al., 2021). In fisheries science, the condition factor (K) is used to compare the “condition”, i.e., fatness or wellbeing of fish (Seher and Suleyman, 2012, Getso et al., 2017). Besides, digestion of food items in fishes depends on the feeding habitats and selection of foods (Pandian, 1967). Evacuation of stomach and digestion govern the feeding in fishes in the form of appetite (Miner, 1955). The relative length of gut (RLG) and Gastro Somatic Index (Ga.SI) defines the feeding nature of a fish species (Lloret and Planes, 2003).
       
Study of reproductive biology of any fish species is essential for assessing commercial potentiality of its stock, life history, culture practice and actual management of its fishery (Doha and Hye, 1970). The gonado-somatic index may vary within a species or even within a sex (Prasad et al., 2011). Fecundity is studied to determine the reproductive capacity of a species concerned. It is studied both in relative as well as absolute context. Relative fecundity is the number of eggs per unit body weight. Absolute (total) fecundity is the total number of eggs that are likely to be spawned in one spawning season.
       
The present study aims to discern certain aspects of morphology, feeding, length-weight relationship, condition factor and reproductive parameters of four economically important fish species Channa punctata, Channa gachua, Mystus cavasius and Mystus vittatus of Upper Brahmaputra basin, Assam. As these fish species are highly favoured by North-eastern people for its significant food and ornamental value. And there is paucity of information on detailed biology and wellness of the fishes in their habitats. Hence, this study will aid in establishing proper strategies for the conservation and sustainable production of the fishes in near future.

MATERIALS AND METHODS

Collection of the species
 
A total of 200 (N=50 for each species) specimens of four different indigenous freshwater fish species (Channa punctata, Channa gachua, Mystus cavasius and Mystus vittatus) [Fig 1 (a-d)] were collected from different sampling sites of Upper Assam, India, particularly from Dibrugarh and Jorhat district during September, 2020 to June, 2022 (Fig 2). Fish specimens were collected on seasonal basis following the classification of the India Meteorological Department, i.e. Winter (December-February), Pre-monsoon (March-May), Monsoon (June-September) and Post-monsoon (October-November). Sampling was carried out using drag nets in both lotic and lentic water bodies within the upper Brahmaputra River basin. Additionally, fish specimens were obtained from various fish landing centres located in the districts of Jorhat and Dibrugarh. Immediately after collection, the lengths and weights of the specimens were recorded with the help of a digital vernier calipers and weighing balance. Further, the specimens were preserved in 4-6% formalin. Identification of the specimens was done by following Talwar and Jhingran, (1991) and Jayaram, (2013).

Fig 1(a-d): Collected fish specimens for the experiment.



Fig 2: Geographical locations of the study sites.


       
The morphometric characteristic features were measured in dial vernier caliper nearest up to 0.01 mm and the total weight of the fish specimens were calculated precisely by using a digital electronic balance (Mettler AB54-S). Detailed morphometric and meristic measurements of the specimens were done following Lowe-McConnel, (1971) and Grant and Spain, (1977).
 
Length-weight relationship (LWR)
 
The relationship between length and weight (LWR) of the fish samples were calculated following Huxley, (1924) using the equation:
 
W= aLb
 
The values of constant a and b was estimated using the least-square method applied to the log transformed data as (Ricker, 1973):
 
log W= log a + b log L
 
Where,
W (g) = Body weight of the fish,
L (cm) = Total length,
a= Intercept of the regression curve.
b = Regression coefficient.
       
Fulton’s condition factor (K) was also estimated to assess the condition of the fishes from the relationship (Beckman, 1948):

 
Where,
W = Weight (g).
L = Total length (cm) of the fish specimens.
 
Feeding and reproductive biology
 
Subsequently, the fishes were dissected in order to obtain their alimentary canal and gonads for studying their feeding behavior and reproductive biology research.
 
Relative gut length
 
The relative gut length (RLG) is measured following Al-Hussaini, (1949):

   
Gastro somatic index (Ga.SI)
 
The Ga.SI is measured following Khan et al. (2018).

 
Gonado somatic index (GSI)
 
The GSI was calculated according to Vazzoler, (1996):

 
Diameter of ova
 
Intra-ovarian eggs were taken out and their diameter was measured under microscope with the help of an ocular micrometer following Clark, (1934).
 
Fecundity
 
The fecundity studies were based on the examination of ripe gonads. 100 mg sub-samples of eggs were carefully detached from the anterior, middle and posterior regions of each ovary with forceps and needle and counted directly under a binocular stereo microscope to determine fecundity (Saikia et al., 2022). The absolute fecundity of the fish was obtained by using the formula given by Legendre (1986):
 
Absolute fecundity = nG /g
 
Where,
n = Number of eggs count in the sub sample.
G = Total weight of the fish.
g = Weight of the sub sample.
       
Relative fecundity was expressed in oocytes per gram following the method of Bagenal, (1978):


Relationship between fecundity and various dimensions such as ovary length and ovary weight were calculated following Bagenal, 1978:
 
Log F = log a + b log X
 
Where,
F = Clutch size (fecundity).
X = Length/Weight.
a = Regression constant.
b = Regression coefficient.
 
Statistical analysis
 
All data have been presented in mean ± SD. Regression equation and correlation coefficient was also calculated following Singh et al. (2021):
 
Y= a + bX
 
Where,
Y =  Dependent variable such as fork length, standard length, body depth etc.
‘a’ = A constant value to be determined.
‘b’ = Regression coefficient.
‘X’ = Independent variable such as total length and head length.
       
All the statistical analysis was done using latest SPSS Tool.

RESULTS AND DISCUSSION

In the present study, detailed morphometric characters of the four important freshwater fish species belonging to the Genus Channa and Mystus have been recorded and presented in Table 1a. In C. gachua (Fig 1a), total lengths (TL) were recorded in the range of 6.5-12.2 cm with a weight range of 2.42-21.18 g. The total length (TL) of C. punctata (Fig 1b) was recorded in between 8.2-14.0 cm with a weight range of 5.0 to 37.8 g. M. cavasius (Fig 1c) recorded the total length in between 9.0 to 15.0 cm and weight from 5.38-31.79 g. And TL of M. vittatus (Fig 1d) was ranged from 5.6 to 8.10 cm and weight from 2.31 to 5.41 g. Range of meristic measurements of the selected four species have been represented in Table 1b. Maximum number of rays ranged from 20-38 recorded in the dorsal fin and lowest 5-6 in ventral fin of C. gachua. Spines were present in dorsal fin and pectoral fin in case of M. cavasius and M. vitttatus.

Table 1: Morphometric measurements (a) and Meristic counts (b) of C. gachua (n=50), C. punctata (n=50), M. cavasius (n=50) and M. vittatus (n=50) of Brahmaputra basin, Assam.


       
The descriptive statistics and estimated parameters of LWRs, ‘a’ and ‘b’ with their 95% of confidence limits, coefficient of correlation (r), coefficient of determination (r2) and condition factor (K) were recorded (Table 2). The highest mean growth coefficient (b) was found in M. cavasius (3.56) and lowest in C. punctata (2.45). The highest correlation coefficient (r) was recorded in M. cavasius (r= 0.964) and lowest in C. punctata (r= 0.886). The values of coefficient of determination (R2) were ranged from 0.78-0.93 (Table 2). Moreover, K-factor ranged from 0.76-1.35 and maximum value was recorded in C. punctata (1.35±0.27) and minimum in Mystus cavasius (0.76±0.10). 

Table 2: Estimated parameters of length-weight relationship and condition factor of C. punctata, C. gachua, M. cavasius and M. vittatus.


       
Values of Ga.SI were found to be ranged from 2.55 - 4.57. Highest value for Ga.SI was recorded in C. punctata (4.57) and lowest in C. gachua (2.55) (Table 3).  Mean absolute fecundity (Table 4) was recorded highest in M. vittatus (3234) and lowest in C. gachua (282). Similarly, mean relative fecundity (Table 4) was found highest in M. vittatus (840) and lowest in C. gachua (22).  Mean GSI found to be ranged from 3.25-63.09. Maximum value for GSI was recorded in M. vittatus (63.09) and lowest in C. gachua (3.25). Mean ova diameter (Table 4) was found highest in C. punctata (0.78) and lowest in M. vittatus (0.49). The relationship between corresponding total body length, total body weight, ovary length and ovary weight of the studied fish species are represented in Table 5. Present study recorded the r value ranged with 0.797-0.891 and highest b value was observed in M. vittatus (b=2.595) followed by Channa gachua (b=2.543).

Table 3: Relative length of gut (RLG) and Gastro-Somatic Index (Ga.SI) of C. punctata, C. gachua, M. cavasius and M. vittatus.



Table 4: Reproductive parameters of C. gachua, C. punctata, M. cavasius and M. vittatus.



Table 5: Regression analysis between total length-weight and ovary length-weight of C. gachua, C. punctata, M. cavasius and M. vittatus.


       
The effective management of aquacultural practice requires considerable knowledge on parameters such as morphometry, length-weight relationship, feeding and reproductive biology. These parameters play a vital role in fisheries biology because it allows proper identification and estimation of average growth of the fish species (Beyer, 1987). In an investigation of some morphometric parameters on 10 fin fish species of Lower Nun River in Niger Delta showed variation in morphometric and meristic indices in different length groups of fish species. Similar results were obtained in the current study. Singh et al., (2021) also observed allometric and isometric growth pattern in Channa stewartii, Heteropneustes fossilis and Trichogaster fasciata of Maijan Beel. Begum et al., (2009) recorded similar findings in the evaluation of length-weight relationship of Mystus spp. Further, Pauly (1993) stated that length-weight relationship (LWR) provides valuable information on the habitat where the fish lives while Kulbicki et al., (2005) stressed the importance of LWR in modelling aquatic ecosystems.
       
In the present investigation, highest b value observed in Mystus cavasius (3.56) indicates positive allometric growth, suggesting that the fish species tends to gain weight at a faster rate relative to its length. This may be attributed to favourable environmental conditions, availability of food resources and species-specific biological characteristics in the upper Brahmaputra basin (Froese, 2006). Conversely, the lowest b value recorded in Channa punctata (2.45) indicating negative allometric growth, where the increase in length is proportionally greater than the increase in weight. Such variation may arise due to ecological factors, seasonal influences, habitat preferences and feeding behaviours of the target species (Singh et al., 2021). Moreover, the relationship of length-weight can be used for estimation of condition factor (K) of the fish species. In fisheries science, the condition factor is used to compare the condition, fitness or wellbeing of fish It is also a useful index for monitoring of feeding intensity, age and growth rates in fish (Ndimele et al., 2011). Condition factor is strongly influenced by both biotic and abiotic environmental factors and hence become an important tool for assessing the status of the aquatic ecosystem in which fish live (Anene, 2005). The present result also supports the findings of Kashyap et al., (2015) in Channa punctatus and Deori et al., (2017) in Trichogaster fasciata.
       
According to Desai and Nair, (2015) food and feeding behaviour of fish diverse as per availability of food, depending on the ecology of the environment. Besides, the relationship between gut and body length is very significant in studying the feeding biology of a fish. The length of the gut determines the feeding nature of a fish i.e. herbivorous fishes have longer gut as compared to the carnivorous fishes (Ribble and Smith, 1983; Horn, 1989; Starck, 2005). In the present study, the RLG value varies from 0.23-0.71 and 0.32-0.93 for the genus Channa and Mystus respectively. Thus, the findings on RLG values depict the carnivorous feeding habit of both the fish species. In the current study, the Ga.SI values ranged in between 2.10-11.869 and 1.09-9.372 in C. punctata and C. gachua respectively. There is a gradual decrease in the Gastro Somatic Index (Ga.SI) as the fish grows through the juvenile stage to the adult stage. Similar results were also recorded in C. punctata collected from water bodies of Surguja, Chattisgarh (Baghel et al., 2019).
               
The Gonado Somatic Index (GSI) observed in the present study (5.579±3.16 and 3.250±1.24 in female C. punctata and C. gachua respectively) is slightly higher than other findings. This is may be due to spawning season of the fishes. Fecundity varies among individuals of the same species depending upon various factors like size, age, condition, genetic potential etc. (Alam and Pathak, 2010). In the present study, the absolute fecundity of C. punctata and C. gachua ranged from 141-2323 eggs and 90-1017 eggs. However, Prasad et al., (2011) reported the absolute fecundity varied from 3,678-27,853 with an average value of 12,546 in the individuals of C. punctatus collected from river Varuna, India. In M. cavasius and M. vittatus, the absolute fecundity ranged from 1340-7789 and 992-6137 respectively. Roy and Hossain, (2006) also reported the fecundity of M. cavasius to be 4,026-25,960. This variation could be due to physiological condition, competition of fish i.e. high mortality and population sample. 

CONCLUSION

The North-eastern region of India is blessed with tremendous biodiversity, though fewer studies have been made so far on its aquatic organisms. Our approach is concerned with the study on certain aspects of biology in relation to morphometric and meristic measurements, feeding and reproductive biology of four native fish species of upper Brahmaputra river basin. The study on length-weight relationship and condition factor of the selected fish species will help in understanding the health status of these fishes in upper Brahmaputra River ecosystem. The knowledge of feeding and reproductive biology will help in establishing the hatcheries and aquaculture management. Moreover, inferences drawn from the present investigation will help in future studies to understand their population dynamics, physiology and growth pattern which will enable to conduct proper management, conservation strategies and sustainable utilization of these species.

ACKNOWLEDGEMENT

The authors are grateful to the Department of Life Sciences, Dibrugarh University for providing necessary facilities and support to carry out the work. 

CONFLICT OF INTEREST

The authors declare that there is no conflict of interest regarding the publication of this paper.

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    Full Research Article

    Study on Certain Aspects of Biology, Length-weight Relationship and Condition Factor of Native Fish Species from Upper Brahmaputra River Basin, India

    M
    Moirangthem Kameshwor Singh1,*
    S
    Simi Gogoi1
    C
    Chandopal Saikia1,2
    S
    Susmita Sonowal1,3
    N
    Netranjally Saikia1
    E
    Emon Thakuria1
    S
    Sanabam Sujen Singh4
    1Department of Life Sciences, Dibrugarh University, Dibrugarh- 786 004, Assam, India.
    2Department of Zoology, Tingkhong College, Dibrugarh-786 612, Assam, India.
    3Department of Zoology, Barnagar College, Sorbhog-781 317, Assam, India.
    4North Eastern Council, Government of India, Shillong- 793 003, Meghalaya, India.

    ABSTRACT

    Background: The present study deals with the morphometric characters, feeding behavior (RLG and Ga.SI), length-weight relationship (LWR), condition factor (K) and reproductive parameters of four native fish species viz. Channa punctata, Channa gachua, Mystus cavasius and Mystus vittatus collected from upper Brahmaputra river basin, Assam. The Brahmaputra river system in northeast India is a global hotspot for aquatic fauna that shelters a rich and diverse gene pool, especially fish.

    Methods: The detailed morphometric characters and meristic counts of the selected fish species (Total=200, n=50 for each species) were measured carefully. Twenty-six morphometric and seven meristic parameters were studied for each fish specimen. The study also examined feeding biology (relative gut length and gastro-somatic index) as well as key reproductive characters viz. gonadosomatic index, absolute and relative fecundity and ova diameter. Regression analysis between total body length and weight, ovary length and weight of the selected specimens have also been performed during the study.

    Result: Present study recorded highest total length in M. cavasius (9.00-15.00 cm) and lowest in M. vittatus (5.60-8.10 cm). The RLG was observed highest in M. cavasius (0.631) and lowest in both C. gachua and M. vittatus (0.45). The regression coefficient (b) indicates negative allometric growth in C. punctata (b= 2.453) and M. vittatus (b= 2.849), while isometric growth was observed in C. gachua (b=3.064) and positive allometric growth in M. cavasius (b= 3.563). Moreover, the r-values for LWRs for all investigated fishes were found ≥ 0.88. The mean condition factor ranged from 0.76-1.35 in all the studied fish species reveals the good health status of the fishes. Absolute fecundity was recorded highest in M. vittatus (3234) and lowest in C. gachua (282). Similarly, relative fecundity was found highest in M. vittatus (840) and lowest in C. gachua (22). Mean GSI was recorded in the ranged of 3.25-63.09. Ova diameter was varied from 0.4-1.2 (cm). Regression analysis between total body length-weight and ovary length-weight of the selected species were also performed and observed strong and positive correlation (r value ranged from 0.797-0.891).

    INTRODUCTION

    The North-eastern Himalayan region is identified as one of the mega aquatic biodiversity hotspots of India. The Brahmaputra riverine system is enriched with diversified freshwater fish species and serves as lifeline of natural fisheries. These fishes have great significance in the life of mankind, being an important natural source of protein and providing certain other useful products as well as economic sustenance to many nations. It is a well-known fact that the knowledge on fish biology particularly on morphometry-meristic, length-weight relationship, condition factor, food and feeding habit, reproduction, etc. is of utmost importance not only to fill up the lacuna of our present-day academic knowledge but also in the utility of the knowledge in increasing the technological efficiencies of the fishery entrepreneurs for evolving judicious pisciculture management. Fish identification depends mostly on two main features: morphometric and meristic characters. Morphometric parameters of a fish species have a major role to ensure whether there is any disparity between the same species of different geographic regions (Naeem et al., 2012; Gogoi et al., 2025). Moreover, some variations may occur in the meristic counts (the number of spines and rays) or in the biometric indices i.e. in different body proportions in various length groups. Length-weight relationship, as a tool for fish conservation, is also crucial to the fish biologist. Estimation of length-weight relationship (LWR) is also considered to be a regular research work of fisheries scientists and has a wide range of application in the field of fish population dynamics (Froese, 2006). It helps to describe some of the basic biological characteristics and provide information on growth status of fishes (Tesch, 1968). Condition factor (K) is an important biological parameter, which indicates the suitability of a specific water body for growth of fish and an index of species average size (Alam et al., 2014, Nayak et al., 2021). In fisheries science, the condition factor (K) is used to compare the “condition”, i.e., fatness or wellbeing of fish (Seher and Suleyman, 2012, Getso et al., 2017). Besides, digestion of food items in fishes depends on the feeding habitats and selection of foods (Pandian, 1967). Evacuation of stomach and digestion govern the feeding in fishes in the form of appetite (Miner, 1955). The relative length of gut (RLG) and Gastro Somatic Index (Ga.SI) defines the feeding nature of a fish species (Lloret and Planes, 2003).
           
    Study of reproductive biology of any fish species is essential for assessing commercial potentiality of its stock, life history, culture practice and actual management of its fishery (Doha and Hye, 1970). The gonado-somatic index may vary within a species or even within a sex (Prasad et al., 2011). Fecundity is studied to determine the reproductive capacity of a species concerned. It is studied both in relative as well as absolute context. Relative fecundity is the number of eggs per unit body weight. Absolute (total) fecundity is the total number of eggs that are likely to be spawned in one spawning season.
           
    The present study aims to discern certain aspects of morphology, feeding, length-weight relationship, condition factor and reproductive parameters of four economically important fish species Channa punctata, Channa gachua, Mystus cavasius and Mystus vittatus of Upper Brahmaputra basin, Assam. As these fish species are highly favoured by North-eastern people for its significant food and ornamental value. And there is paucity of information on detailed biology and wellness of the fishes in their habitats. Hence, this study will aid in establishing proper strategies for the conservation and sustainable production of the fishes in near future.

    MATERIALS AND METHODS

    Collection of the species
     
    A total of 200 (N=50 for each species) specimens of four different indigenous freshwater fish species (Channa punctata, Channa gachua, Mystus cavasius and Mystus vittatus) [Fig 1 (a-d)] were collected from different sampling sites of Upper Assam, India, particularly from Dibrugarh and Jorhat district during September, 2020 to June, 2022 (Fig 2). Fish specimens were collected on seasonal basis following the classification of the India Meteorological Department, i.e. Winter (December-February), Pre-monsoon (March-May), Monsoon (June-September) and Post-monsoon (October-November). Sampling was carried out using drag nets in both lotic and lentic water bodies within the upper Brahmaputra River basin. Additionally, fish specimens were obtained from various fish landing centres located in the districts of Jorhat and Dibrugarh. Immediately after collection, the lengths and weights of the specimens were recorded with the help of a digital vernier calipers and weighing balance. Further, the specimens were preserved in 4-6% formalin. Identification of the specimens was done by following Talwar and Jhingran, (1991) and Jayaram, (2013).

    Fig 1(a-d): Collected fish specimens for the experiment.



    Fig 2: Geographical locations of the study sites.


           
    The morphometric characteristic features were measured in dial vernier caliper nearest up to 0.01 mm and the total weight of the fish specimens were calculated precisely by using a digital electronic balance (Mettler AB54-S). Detailed morphometric and meristic measurements of the specimens were done following Lowe-McConnel, (1971) and Grant and Spain, (1977).
     
    Length-weight relationship (LWR)
     
    The relationship between length and weight (LWR) of the fish samples were calculated following Huxley, (1924) using the equation:
     
    W= aLb
     
    The values of constant a and b was estimated using the least-square method applied to the log transformed data as (Ricker, 1973):
     
    log W= log a + b log L
     
    Where,
    W (g) = Body weight of the fish,
    L (cm) = Total length,
    a= Intercept of the regression curve.
    b = Regression coefficient.
           
    Fulton’s condition factor (K) was also estimated to assess the condition of the fishes from the relationship (Beckman, 1948):

     
    Where,
    W = Weight (g).
    L = Total length (cm) of the fish specimens.
     
    Feeding and reproductive biology
     
    Subsequently, the fishes were dissected in order to obtain their alimentary canal and gonads for studying their feeding behavior and reproductive biology research.
     
    Relative gut length
     
    The relative gut length (RLG) is measured following Al-Hussaini, (1949):

       
    Gastro somatic index (Ga.SI)
     
    The Ga.SI is measured following Khan et al. (2018).

     
    Gonado somatic index (GSI)
     
    The GSI was calculated according to Vazzoler, (1996):

     
    Diameter of ova
     
    Intra-ovarian eggs were taken out and their diameter was measured under microscope with the help of an ocular micrometer following Clark, (1934).
     
    Fecundity
     
    The fecundity studies were based on the examination of ripe gonads. 100 mg sub-samples of eggs were carefully detached from the anterior, middle and posterior regions of each ovary with forceps and needle and counted directly under a binocular stereo microscope to determine fecundity (Saikia et al., 2022). The absolute fecundity of the fish was obtained by using the formula given by Legendre (1986):
     
    Absolute fecundity = nG /g
     
    Where,
    n = Number of eggs count in the sub sample.
    G = Total weight of the fish.
    g = Weight of the sub sample.
           
    Relative fecundity was expressed in oocytes per gram following the method of Bagenal, (1978):


    Relationship between fecundity and various dimensions such as ovary length and ovary weight were calculated following Bagenal, 1978:
     
    Log F = log a + b log X
     
    Where,
    F = Clutch size (fecundity).
    X = Length/Weight.
    a = Regression constant.
    b = Regression coefficient.
     
    Statistical analysis
     
    All data have been presented in mean ± SD. Regression equation and correlation coefficient was also calculated following Singh et al. (2021):
     
    Y= a + bX
     
    Where,
    Y =  Dependent variable such as fork length, standard length, body depth etc.
    ‘a’ = A constant value to be determined.
    ‘b’ = Regression coefficient.
    ‘X’ = Independent variable such as total length and head length.
           
    All the statistical analysis was done using latest SPSS Tool.

    RESULTS AND DISCUSSION

    In the present study, detailed morphometric characters of the four important freshwater fish species belonging to the Genus Channa and Mystus have been recorded and presented in Table 1a. In C. gachua (Fig 1a), total lengths (TL) were recorded in the range of 6.5-12.2 cm with a weight range of 2.42-21.18 g. The total length (TL) of C. punctata (Fig 1b) was recorded in between 8.2-14.0 cm with a weight range of 5.0 to 37.8 g. M. cavasius (Fig 1c) recorded the total length in between 9.0 to 15.0 cm and weight from 5.38-31.79 g. And TL of M. vittatus (Fig 1d) was ranged from 5.6 to 8.10 cm and weight from 2.31 to 5.41 g. Range of meristic measurements of the selected four species have been represented in Table 1b. Maximum number of rays ranged from 20-38 recorded in the dorsal fin and lowest 5-6 in ventral fin of C. gachua. Spines were present in dorsal fin and pectoral fin in case of M. cavasius and M. vitttatus.

    Table 1: Morphometric measurements (a) and Meristic counts (b) of C. gachua (n=50), C. punctata (n=50), M. cavasius (n=50) and M. vittatus (n=50) of Brahmaputra basin, Assam.


           
    The descriptive statistics and estimated parameters of LWRs, ‘a’ and ‘b’ with their 95% of confidence limits, coefficient of correlation (r), coefficient of determination (r2) and condition factor (K) were recorded (Table 2). The highest mean growth coefficient (b) was found in M. cavasius (3.56) and lowest in C. punctata (2.45). The highest correlation coefficient (r) was recorded in M. cavasius (r= 0.964) and lowest in C. punctata (r= 0.886). The values of coefficient of determination (R2) were ranged from 0.78-0.93 (Table 2). Moreover, K-factor ranged from 0.76-1.35 and maximum value was recorded in C. punctata (1.35±0.27) and minimum in Mystus cavasius (0.76±0.10). 

    Table 2: Estimated parameters of length-weight relationship and condition factor of C. punctata, C. gachua, M. cavasius and M. vittatus.


           
    Values of Ga.SI were found to be ranged from 2.55 - 4.57. Highest value for Ga.SI was recorded in C. punctata (4.57) and lowest in C. gachua (2.55) (Table 3).  Mean absolute fecundity (Table 4) was recorded highest in M. vittatus (3234) and lowest in C. gachua (282). Similarly, mean relative fecundity (Table 4) was found highest in M. vittatus (840) and lowest in C. gachua (22).  Mean GSI found to be ranged from 3.25-63.09. Maximum value for GSI was recorded in M. vittatus (63.09) and lowest in C. gachua (3.25). Mean ova diameter (Table 4) was found highest in C. punctata (0.78) and lowest in M. vittatus (0.49). The relationship between corresponding total body length, total body weight, ovary length and ovary weight of the studied fish species are represented in Table 5. Present study recorded the r value ranged with 0.797-0.891 and highest b value was observed in M. vittatus (b=2.595) followed by Channa gachua (b=2.543).

    Table 3: Relative length of gut (RLG) and Gastro-Somatic Index (Ga.SI) of C. punctata, C. gachua, M. cavasius and M. vittatus.



    Table 4: Reproductive parameters of C. gachua, C. punctata, M. cavasius and M. vittatus.



    Table 5: Regression analysis between total length-weight and ovary length-weight of C. gachua, C. punctata, M. cavasius and M. vittatus.


           
    The effective management of aquacultural practice requires considerable knowledge on parameters such as morphometry, length-weight relationship, feeding and reproductive biology. These parameters play a vital role in fisheries biology because it allows proper identification and estimation of average growth of the fish species (Beyer, 1987). In an investigation of some morphometric parameters on 10 fin fish species of Lower Nun River in Niger Delta showed variation in morphometric and meristic indices in different length groups of fish species. Similar results were obtained in the current study. Singh et al., (2021) also observed allometric and isometric growth pattern in Channa stewartii, Heteropneustes fossilis and Trichogaster fasciata of Maijan Beel. Begum et al., (2009) recorded similar findings in the evaluation of length-weight relationship of Mystus spp. Further, Pauly (1993) stated that length-weight relationship (LWR) provides valuable information on the habitat where the fish lives while Kulbicki et al., (2005) stressed the importance of LWR in modelling aquatic ecosystems.
           
    In the present investigation, highest b value observed in Mystus cavasius (3.56) indicates positive allometric growth, suggesting that the fish species tends to gain weight at a faster rate relative to its length. This may be attributed to favourable environmental conditions, availability of food resources and species-specific biological characteristics in the upper Brahmaputra basin (Froese, 2006). Conversely, the lowest b value recorded in Channa punctata (2.45) indicating negative allometric growth, where the increase in length is proportionally greater than the increase in weight. Such variation may arise due to ecological factors, seasonal influences, habitat preferences and feeding behaviours of the target species (Singh et al., 2021). Moreover, the relationship of length-weight can be used for estimation of condition factor (K) of the fish species. In fisheries science, the condition factor is used to compare the condition, fitness or wellbeing of fish It is also a useful index for monitoring of feeding intensity, age and growth rates in fish (Ndimele et al., 2011). Condition factor is strongly influenced by both biotic and abiotic environmental factors and hence become an important tool for assessing the status of the aquatic ecosystem in which fish live (Anene, 2005). The present result also supports the findings of Kashyap et al., (2015) in Channa punctatus and Deori et al., (2017) in Trichogaster fasciata.
           
    According to Desai and Nair, (2015) food and feeding behaviour of fish diverse as per availability of food, depending on the ecology of the environment. Besides, the relationship between gut and body length is very significant in studying the feeding biology of a fish. The length of the gut determines the feeding nature of a fish i.e. herbivorous fishes have longer gut as compared to the carnivorous fishes (Ribble and Smith, 1983; Horn, 1989; Starck, 2005). In the present study, the RLG value varies from 0.23-0.71 and 0.32-0.93 for the genus Channa and Mystus respectively. Thus, the findings on RLG values depict the carnivorous feeding habit of both the fish species. In the current study, the Ga.SI values ranged in between 2.10-11.869 and 1.09-9.372 in C. punctata and C. gachua respectively. There is a gradual decrease in the Gastro Somatic Index (Ga.SI) as the fish grows through the juvenile stage to the adult stage. Similar results were also recorded in C. punctata collected from water bodies of Surguja, Chattisgarh (Baghel et al., 2019).
                   
    The Gonado Somatic Index (GSI) observed in the present study (5.579±3.16 and 3.250±1.24 in female C. punctata and C. gachua respectively) is slightly higher than other findings. This is may be due to spawning season of the fishes. Fecundity varies among individuals of the same species depending upon various factors like size, age, condition, genetic potential etc. (Alam and Pathak, 2010). In the present study, the absolute fecundity of C. punctata and C. gachua ranged from 141-2323 eggs and 90-1017 eggs. However, Prasad et al., (2011) reported the absolute fecundity varied from 3,678-27,853 with an average value of 12,546 in the individuals of C. punctatus collected from river Varuna, India. In M. cavasius and M. vittatus, the absolute fecundity ranged from 1340-7789 and 992-6137 respectively. Roy and Hossain, (2006) also reported the fecundity of M. cavasius to be 4,026-25,960. This variation could be due to physiological condition, competition of fish i.e. high mortality and population sample. 

    CONCLUSION

    The North-eastern region of India is blessed with tremendous biodiversity, though fewer studies have been made so far on its aquatic organisms. Our approach is concerned with the study on certain aspects of biology in relation to morphometric and meristic measurements, feeding and reproductive biology of four native fish species of upper Brahmaputra river basin. The study on length-weight relationship and condition factor of the selected fish species will help in understanding the health status of these fishes in upper Brahmaputra River ecosystem. The knowledge of feeding and reproductive biology will help in establishing the hatcheries and aquaculture management. Moreover, inferences drawn from the present investigation will help in future studies to understand their population dynamics, physiology and growth pattern which will enable to conduct proper management, conservation strategies and sustainable utilization of these species.

    ACKNOWLEDGEMENT

    The authors are grateful to the Department of Life Sciences, Dibrugarh University for providing necessary facilities and support to carry out the work. 

    CONFLICT OF INTEREST

    The authors declare that there is no conflict of interest regarding the publication of this paper.

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