Length-Weight and Length-Length relationship of two tropical freshwater fish species from Central Brahmaputra Valley, Assam

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- Bhargav Nath, Jyotirmoyee Das, Abdul Malik Ahmed, Jiten Sharma, Bipul Phukan. Ayub Ali, Arup Kumar Sharma & Simanta Borah, MSc, College of Fisheries, AAU

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ABSTRACT : The present study was carried out to establish the relationship between total length (TL) and total body  weight (BW) and relationship between total length (TL), standard length (SL) and fork length (FL) for two native fish species from Kolong river, Nagaon, Assam, India. A total of 676 specimens comprising Mystus cavasius (n=285) and Cirrhinus reba (n=391) were collected for the study. The relationship between TL, SL and FL was found to be linear for both the species. The b value for the two fish species was found to be 2.42 for M. cavasius and 2.79 for C. reba. Information on length-weight and length-length relationship of M. cavasius and C. reba from Brahmaputra basin are quite limited. Besides, no such information was found for these two species from Kolong river, Nagaon, Assam and thus, information generated in the present study can be helpful in sustainable management of these resources.

Key words : Length-weight relationship, length-length relationship, Mystus cavasius, Cirrhinus reba, Kolong river, Assam.



The mighty river Brahmaputra, which is the lifeline of Assam rises from Chemayungdung Mountain about 100 km South East of Manasorovar Lake in Tibet and runs for a distance of 1250 km in Tibet as Tsangpo. It enters India near Tuting in Siang district, Arunachal
Pradesh, where it is known as Siang or Dihang; enters Assam at Sadiya where it meets two other Himalayan rivers namely Dibang and Lohit and assumes the name Brahmaputra. The river finally drains into the Bay of Bengal via Bangladesh (Vaas and Moza, 2011). The total length of Brahmaputra river is 2900 km of which 900 km falls in India of which 640 km lies in Assam. A total of 141 finfish species belonging to 84 genera and 29 families are reported from this river in Assam (Bhattacharjya et
al, 2017). It is drained by 41 major tributaries of which 25 are on the northern bank and 16 on the southern bank in the Indian part. Kolong, a distributary of river Brahmaputra with a total length of about 250 km, originates from Brahmaputra, between the two hills of Hatimura and Barjhap near Jakhalabandha (Nagaon district, Assam) at 26°36’03″N latitude and 93°05’7″E longitude. This river meets Kopili, a major south bank tributary of Brahmaputra near Jagibhakatgaon and finally drains into Brahmaputra at Kajalimukh (Bora and Goswami, 2015). Length-weight relationship (LWR) and length-length relationship (LLR) have been widely applied in the fieldof fish biology in order to carry out studies on fish stock assessment (Ricker, 1975). Length-weight relationship is
one of the scientifictools for demonstrating the survival, growth, maturity, reproduction, and general well-being of fishes (Le Cren, 1951). Length-weight relationship (LWR) are useful in fishery management for both applied and basic use such as estimate weight from length observations, calculate production and biomass of a fish population and also provide information on stocks or organisms condition at the corporal level (Hossain et al,2014). Mystus cavasius (Hamilton-Buchanan, 1822) is considered as one of the most important fish among indigenous catfish under family Bagridae of order Siluriformes. It is commonly known as ‘Gangetic Mystus’ which has been reported to be distributed in Pakistan, Bangladesh, India, Myanmar, Sri Lanka and Nepal (Jayaram, 1977; Jhingran, 1991; Rahmen et al, 2012). Cirrhinus reba (Hamilton, 1822) is also an important indigenous species, commonly known as ‘reba carp’ and it is one of the most popular food fishes widely distributed in India, Bangladesh, Pakistan, Nepal, Burma and Thailand (Mathialagan et al, 2014). M. cavasius has been listed as Lower Risk Near Threatened (LRnT), while C. reba has been listed as Vulnerable (VU) as per CAMP (1998).

The present study is an attempt to provide basic information on the growth of these two fish species based on LLR and LWR studies. Basic information on the length-weight relationship and length-length relationship for these two important native species of Kolong river will be helpful for future studies. Not much information is available on this aspect from Kolong River in particular and Central Brahmaputra valley in general. The present study is a maiden attempt in this region and the results obtained from it may contribute significantly to our knowledge of one vulnerable (VU) and one Near Threatened (NT) fish species.


A total of 676 specimens of two species M. cavasius (n = 285) and C. reba (n = 391) were collected for observation of length-weight and length-length relationship from different sides of Kolong river from January to December, 2017. Sampling was carried out on a monthly basis during the period. Fish specimens were caught using gill nets, cast nets and seine nets of varying mesh sizes from 25-40 mm from two different landing centers (near Raha and Chaparmukh) of Kolong river in Nagaon district of Assam. The collected fishes were packed in ice filled boxes and brought to the laboratory for further observation. In the laboratory body measurement of fish specimens were taken. Total length (TL), Standard length (SL) and Fork length (FL) of specimens were measured to the nearest 1 mm by scale and body weight (BW) was measured with digital weighing machine with the precision of 0.1 mg using Sartorius BSA224S-CW electronic balance.

After removing all the outliers following, Froese (2006), the length-weight relationship was estimated by using cube law given by Le Cren (1951)

W = aLb

Length-weight relationship of each fish species was worked out using the logarithmic transformation of cube law in order to arrive at a linear relationship.

Log W = Log a + b Log L

Where, W is the weight of the fish in grams (g), L is the total length of fish in millimetres (mm), ‘a’ and ‘b’ are intercept and slope of regression line, respectively. To test for possible significant differences in both slope and intercept, analysis of co-variance was followed. Relationship between Total length (TL) and Standard length (SL), Standard length (SL) and Fork length (FL), Fork length (FL) and Total length (TL) were established using linear regression analysis of TL = a + b × SL; SL = a + b × FL; FL = a + b × TL, respectively.


Length-weight relationship for the fish species were found to be significant at 1% and 5% level. The b value for the two fish species were found to be 2.42 for M. cavasius and 2.79 for C. reba (Table 1). Studies on the Length-length relationship showed that the relationship between Total length (TL), Standard length (SL) and Fork length (FL) was found to be linear for all cases and significant (p£0.01) (Table 2).


Froese et al (2011) highlighted the importance of studies on LWR in the field of fisheries science and management. Attempts are being made to study LWRs and LLRs of tropical freshwater fishes from Ganga and Brahmaputra basin of India (Borah et al, 2017; Nath et al, 2017; Baitha et al, 2018; Koushlesh et al, 2018; Borah et al, 2018). Information on length-weight and length- length relationship of Mystus cavasius and Cirrhinus reba are quite limited from Brahmaputra basin and no such information was found for these two species from Kolong river, Assam. In the present investigation, the exponential form of the equation derived for the length-weight relationship of M. cavasius was found to be W = 0.0312 L2.4235 (r2 = 0.9022). The respective linear relationship could be expressed as Log W = 0.0312 + 2.4235 Log L. According to Soomro et al (2015), a total of 391 specimens of Mystus cavasius were used and ‘b’ value was calculated as 2.54, which indicate negative allometric growth of the species. In a recent study on the length- weight relationship of Mystus cavasius, Latif et al (2018) reported that the regression coefficient ‘b’ was 2.71 indicating negative allometric growth of this fish.

In case of C. reba, length-weight relationship was found to be W = 0.0218 L2.7984 (r2 = 0.9494) and the respective linear relationship could be expressed as Log W = 0.0218 + 2.7984 Log L. Mathialagan et al (2014) reported a ‘b’ value of 2.363 in C. reba. For both the studied species, b value was found to be in the expected range of 2.5-3.5 (Froese, 2006). However, deviations in b value for both the species as compared to previous 

Length-weight and length-length relationship of two tropical
freshwater fishes species                            323

Table 1 : Descriptive statistics and estimated length-weight relationship
parameters for two indigenous fish species during the experimental period.


Fish species


Length range (cm)

Weight range (g)

Regression parameters


95% confidence level of a


95% confidence level of b


Mystus cavasius









Cirrhinus reba









N: sample size;
a: intercept; b: slope; r2: coefficient of determination.

Table 2 : Estimation of length-length relationship between Total length
(TL), Standard length (SL) and Fork length (FL) for two indigenous fish species
during the experimental period.


Fish species


TL=a + b SL

SL= a + b FL

FL = a + b TL










Mystus cavasius











Cirrhinus reba











N: sample size;
TL: total length; SL: standard length, FL: fork length; a: intercept; b: slope;
r2: coefficient of determination.


can be attributed to multiple factors like sample size and length range of specimens
examined, habitat of fish, maturity stages, sex, diet,
growth phase, stomach fullness and seasonality (Froese, 2006). The exponent ‘b
value was significantly lower than 3 (P<0.01) indicating negative allometric growth pattern for both M. cavasius and C. reba. The value
of b if more
than 3 is an indication that fish will become plump
with increasing and value less than 3 means more and more slender bodied fish
as length increases (Jobling, 2002). The value
of ‘b’ for both the fish species are found to be below 3.0 that show that the rate of increase in body length
is not proportional to the rate of increase in body weight.
This change may be
attributed to various factors which affect the growth of fish such as
season, habitat, gonadal maturity, sex,
stomach fullness, health and preservation techniques (Soomro et al,

Length-length relationship is important in the fisheries management
for comparative growth  studies
(Moutopoulos and Stergiou, 2002). Variations
in LLRs of same species from across different locations may be
attributed to varying ecological conditions and variation in the physiology of the animals,
or a combination of both (Le Cren, 1951). The regional
difference in total length or standard length or fork length probably depends
on ecological condition in the area of investigation (Noor, 2013). In the present
study, the values
for co-efficient of determination (r2) for all the length-length parameters of the two
species M. cavasius and C. reba were greater than 0.9 and were found to be linear and highly significant
(P<0.01) (Table 1).
Muhammad et al (2016) studied the
length-length relationship (TL, SL and FL) of C. reba and reported that the length-length relationship for this
species is linear, which supports
the data obtained
in the


study. Nath et al (2017) also studied the length- length relationship of C. reba in Barak river, Assam,
and found that the relationship was linear.


This study has provided some basic information on the
length-weight and length-weight relationships for Mystus cavasius and Cirrhinus
that will be helpful to fishery
biologists. Mystus cavasius and
Cirrhinus reba exhibited different
growth patterns and showed a strong
association between length and
weight. Not much information is available on its length-weight and length- length
relationship from Central Brahmaputra valley, Assam. Information generated in
the present study can be helpful in sustainable management of these resources, besides acting as baseline
information for future


The authors are thankful to Dean, College of Fisheries, Assam
Agricultural University, Raha, for his kind co-operation and
providing all the necessary facilities
to carry out the research
work. Valuable suggestions and help
rendered from Head and principal
Scientist, Central Inland Fisheries Resource Institute, HOUSEFED Complex Guwahati centre,
during my research
period is deeply acknowledged. The authors also thankful
to thefishermen of Kolong River
for their co-operation.


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