This study describes length-weight and length-length relationships of four species (Labeo bata, Channa punctata, Ompok pabda and Mastacembelus armatus) collected from river Ganga. A total of 856 specimens were examined for the study. Length-Weight Relationship (LWR) indicated isometric pattern of growth for L. bata, positive allometric growth for O. pabda and C. punctata while negative allometric growth for M. armatus. Length-length relationships (LLR) for all the four species were highly significant (R2>0.9, p<0.001). For two species length-weight and length-length relationships were not available on FishBase.
How to cite this article:
M. Afzal Khan, Shahista Khan and Kaish Miyan, 2012. Studies on Length-weight and Length-length Relationships of Four Freshwater Fishes Collected from River Ganga. Journal of Fisheries and Aquatic Science, 7: 481-484.
The length-weight and length-length relationships have been applied for the assessment of fish stocks and populations (Ricker, 1968). The weight-length relationship and its parameters (a and b) have a wide application in fish biology and fisheries management, ranging from the estimation of weight from length data (or vice versa) (Le Cren, 1951; Anderson and Gutreuter, 1983; Petrakis and Stergiou, 1995; Froese, 2006) to the calculation of production and biomass of a fish population (Giacalone et al., 2010). LWR is also useful in local and interregional, morphological and life historical comparisons in species and populations (Kara and Bayhan, 2008). There are a number of length-weight reports available on freshwater fishes collected from river Ganga (Sarkar et al., 2009; Khan et al., 2011, 2012). However, such data on selected fish species (Channa punctata, Labeo bata, Ompok pabda and Mastacembelus armatus) from river Ganga is not available.
In the present study, we report the Length-Weight Relationship (LWR) and Length-Length Relationship (LLR) for four fish species collected from the river Ganga. Fishes selected for the present study are Channa punctata (Bloch), Labeo bata (Hamilton), Ompok pabda (Hamilton) and Mastacembelus armatus (Lacepede). Of the four species selected for the study, two species are listed in the category of Lower Risk-near threatened (LR-nt) (L. bata and C. punctata), one as Endangered (O. pabda) (Molur and Walker, 1998) and one as Least concern (M. armatus) in India (IUCN, 2011). Studies on Length-Weight Relationships (LWRs) and Length-Length Relationships (LLRs) of threatened fishes are the most important biological parameters to provide information on the growth and condition of fish species and the entire fish community and are highly significant for management and conservation of populations in natural water bodies (Sarkar et al., 2009; Hossain et al., 2012). To the best of our knowledge, no previous reports of length-weight and length-length relationships on these fish species are available from the selected river. Further, FishBase database (Froese and Pauly, 2012) showed no record of length-weight and length-length relationships for two fish species (L. bata and O. pabda).
MATERIALS AND METHODS
Fish specimens were collected monthly from the river Ganga using nets of various mesh sizes from January 2010 to January 2012. The river Ganga rises in the Gangotri glacier (30°54'N; 78°54'E) in the Himalayas at an altitude of 7010 m above mean sea level in Uttarkashi district of Uttarakhand, India. It travels along the five Indian states of Uttarakhand, Uttar Pradesh, Jharkhand, Bihar and West Bengal. All species were identified according to Talwar and Jhingran (1991), Jayaram (1999) and rechecked against FishBase database (Froese and Pauly, 2012). Total Length (TL), Fork Length (FL) and Standard Length (SL) of all fish samples were measured to the nearest 0.1 cm. Body weight was recorded as Total Weight (TW) including gut and gonads to the nearest 0.1 g. Sex was macroscopically determined by gonad examination.
The length-weight relationship is described by the equation W = a Lb, where W is the total weight in grams, L is the total length in centimeters, a is the intercept and b is the regression coefficient (Froese, 2006). For each species, the parameters a, b and R2 (coefficient of determination) was estimated by least-squares regression analysis of the logarithm-transformed LWR expression log W = log a+b log L (Garcia, 2010). Standard Length (SL) and Fork Length (FL) were also measured to the nearest cm to make the relationships TL vs SL, SL vs FL and FL vs TL by linear regression (Hossain et al., 2006). All statistical analyses were done using MS-Excel and SPSS (version 17.0).
RESULTS AND DISCUSSION
Length-weight relationships were calculated for a total of 856 individuals of four species belonging to four different families (Channidae, Cyprinidae, Mastacembelidae, Siluridae). The parameters of the length-weight relationship for each species are given in Table 1, together with the regression coefficient (R2), the number of specimens measured (n), standard error of slope b and the total size of the smallest (min) and largest (max) specimens measured.
|Table 1:||Parameters of length-weight relationship of four fish species collected from river Ganga|
|N: Total No. of samples, a: Intercept, b: Slop, R2: Coefficient of determination, *Anti-log a, 1Length-weight relationship of parameters reported in FishBase|
|Table 2:||Parameters of length-length relationship of four fish species collected from river Ganga|
|TL: Total length, FL: Fork length, SL: Standard length, R2: Coefficient of determination|
Linear regressions on log transformed data were highly significant (p<0.001) for all analyzed species, showing R2>0.9.
When the specific gravity of a fish remains unchanged and retains the same shape during its lifetime, it is growing isometrically and the value of length exponent b, would be exactly 3.0 (Wootton, 1990). In the present study, calculated allometric coefficient b ranged from a minimum of 2.894 for M. armatus, to a maximum of 3.130 for O. pabda. Froese (1998) recommended that the exponent (b) of the length-weight relationships should fall within the expected range of 2.5-3.5. The results revealed that L. bata (3.021) showed isometric pattern of growth, M. armatus (2.894) showed negative allometric growth (b<3) while C. punctata and O. pabda (3.130) showed positive allometric growth (b>3). A number of factors are known to influence the length-weight relationship in fishes, including growth phase, season, degree of stomach fullness, gonad maturity, sex, size range, health and general fish condition and preservation techniques (Tesch, 1971). However, these factors were not accounted for in the present study. In addition to present study, Table 1 also gives a comparison of published length-weight relationship parameters from other geographical areas. The value of b for L. bata (Chaterjii et al., 1977), O. pabda (Gupta et al., 2011) and C. punctata (Hossain et al., 2006) is different from those reported in the present study. The observed differences in the values may be due to the environmental differences, differences in the utilized types and length ranges or differences in the number of specimen examined.
All LLRs presented in Table 2 were highly significant (p<0.001), with most of the coefficient of determination values being >0.9. In conclusion, this study provides basic information on LWRs and LLRs for four fish species that would be of academic and applied significance.
Authors are thankful to the Chairman, Department of Zoology, Aligarh Muslim University, Aligarh, India for providing necessary facilities for the study.
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